hassgrant

I have a 91 Z28 305 TPI. I checked my TPS voltage today to make sure I am getting proper voltage as the car stumbles on take off and feels like I am dragging something when I try to hard accelerate. This all happens in closed loop. In open loop she has great acceleration response. Anyway, I used my digital voltmeter and backprobed the A and B ports of the TPS with the ignition on, engine off, and was reading less than .3 volts when I think I should be reading closer to .54 volts. At WOT I can't get the TPS to get over 3.5 volts and I should be getting between 4 and 5. Correct me if I am wrong, please. The TPS is only a month old. Is it possible I got a faulty TPS. It is a BWD from Advanced Auto Parts. Someone please help!

RedneckNo4

whats the voltage at C? its probably bad

turbinator3

adjust the tps until you get the proper voltage at closed position which is as you stated. then run it through the range and make sure you gat the right voltage inrease all the way through.

hassgrant

When I probe C and A I get 5.03 and when I probe C and the batt - I get 5.08. When I probe A and B I get .31 and when I probe A and B and try WOT I get 2.63. When I take off the TPS and probe A and B and move the TPS lever as far as it can go (WOT) I get 3.26. So did I get a defective TPS? I hope so because I have been chasing this poor acceleration issue for awhile. Replaced plugs, wires, rotor, cap, O2 sensor, EGR valve, gaskets, knock sensor, IAC, ICM, ECM, and checked for vacuum leaks. I am also not getting a SEL light or throwing any codes when I jump A and B in the ALDL.

darrlee

I am having this same performace problem that you described with my 85 305 TPI. Can someone post the exact prcedure for testing the TPS? Pictures or diagrams would be helpful too.

On yours it sounds like there is an adjustment procedure to the TPS as well. Anyone out there have directions on how to adjust the TPS as well?

hassgrant

The TPS on my vehicle (91 Z28 305 TPI) is non adjustable besides the fact that you can sort of manuever it on the side of the TB as the TPS has oval mounting holes that allow for some play. I tested the resistances on my TPS and got 1.58 ohms from A to B, 5.87 ohms from A to C, and 6.34 ohms from B to C. I am not an electrical engineer so I am not sure if these readings are good or bad.

hassgrant

The part number for the TPS by BWD that I am getting from Advanced Auto Parts is EC3010. I am just putting that out there in case this is not the right part number for the 91 Z28 305 TPI and not designed for the voltage readings I am trying to get. Also, I am curious why my throttle response is so good in open loop and so 'delayed', for lack of a better word, in closed loop. Does the ECM not read the voltage from the TPS in open loop and just adjust fuel for the amount of air coming in from the throttle body? Oh, and I checked vacuum just for ***** and giggles, and I am getting a constant 20 in/Hg at idle and I get the same reading when I pull vacuum plugs and plug the corresponding port. So, I am beginning to rule out vacuum leak as culprit of acceleration issue and I am beginning to think it may be the TPS, and has been the TPS all along.

ASE doc

The test for the TPS is just what you did except we generally use a lab scope to look for glitches or drop outs. The DVOM isn't fast enough to pick up small glitches. However, if you sweep it slowly, you should be able to see any major faults. As far as your voltages go, they are low. Check your battery for 12.6v and check the batt connections too. Also, remember, youre testing with the key on engine off on a 20 year old car. Electrical system voltage is going to read somewhat low without input from the alternator.

As far as I know, the 91 TPS is not adjustable. However, non adjustable TPS usually has round mounting holes. If you have oval or slotted mounting holes, then you may be able to adjust the TPS to some degree. TPS should read .5-.6 at closed throttle and 4.5 at WOT.

To check the non- adjustable TPS you want to use a scan tool and look for Throttle value on datastream. It reads in percent from 0-100. On the non adjustables, the ECM recalibrates 0% TPS every time the key is turned on. On these, specific voltage is not a big issue as long as there are no glitches or drop outs.

The drivability issue you're having sounds more like ignition drop out or maybe injectors. How old are your ignition wires?

hassgrant

Forgot to mention that I replaced the injectors two weeks ago with 19lb Bosch III injectors. Not sure what you mean by ignition wires. I just replaced the spark plug wires with MSD wires last week. My battery reads 12.7 with the VOM. Even understanding that the car is old, the TPS sensor should still read the correct volts as it is getting over 5 volts from the ECM but not returning the necessary volts to the ECM. Currently the TPS is reading about 50% to 60% of what I want. I also checked fuel pressure and I am getting around 38 psi.

ASE doc

Is the 38 psi with or without vacuum to the regulator? Pressure on the 91 should be 45-50 without vacuum. By ignition wires I mean the wires you just replaced with MSD. They're obviously not the problem. Did you verify 5 volts at pin C of the TPS? Check for voltage to ground at pin A. Can you rotate the TPS on its mounting at all?

hassgrant

I appreciate you helping me out with this situation ASE doc, but please read previous posts as I have already posted voltage readings. The fuel pressure was with vacuum to FP regulator and engine at idle. I will get a more accurate reading tomorrow as I am at work right now. When I tried to rotate the TPS as much as I could I could only get upper.3s on VOM and couldn't even get 5 volts with TPS off, plugged in, and the lever moved as far as it would go. This is why I think the TPS is bad as it is getting its 5 volts from the ECM but is returning 3.26 volts when the lever is moved as far as it can go off the TB and plugged in.

RedneckNo4

since it is only a month old you can try and get it replaced for free and in the parking lot at the AAP test your voltages again and see what you get

ASE doc

I appologise for missing the post with all voltages. Definitely looks like a bad sensor.

hassgrant

I am going to pick up the new sensor tomorrow. I have been lucky with Advanced Auto Parts as they have allowed me to warranty all my parts as I chase down certain issues. I will let you know what happens after I swap it out. Thanks again for all input, I really DO appreciate it as there are some really intelligent individuals here that are good enough to share their experiences and wisdom! Hopefully, after I fix this issue, I can get the car painted again and looking good (wrecked her in June and have been rebuilding her ever since).

motortrendz

i would also check for voltage drop or high resistance on the ecm sense signal.. also is your system a speed density or a mas air flow system? just wondering bc you said it works fine in open loop and when it goes into closed loop it acts up, i would want to see the fuel trim both long term and short term.. you may have a bad o2 sensor giving improper readings and can cause the goal trim to be way off causing this issue also..

hassgrant

Well I feel dumb, but I must post my mistake - I was testing the TPS with the VOM at the wrong setting. I was testing it with the VOM at 9V instead of on 20 in the V selection range of the VOM. Weird thing was is that at both settings my battery had the same reading, but the TPS sensor reading is way different. So now, my old sensor is set to .64V (heard a little higher than .54V gives a little bit better response) at idle and goes past 4V (sorry, don't remember exact, but it is higher than 4V but less than 5V) at WOT. I also fixed what might have been a slight vacuum leak at the point where the brake booster connects to the back of the plenum. Had slight airy sound when checked with vacuum hose in my ear like a stethoscope. I also tried to set the minimal air setting but can never get the car to run long enough to really set it. So, I just backed of the adjustment screw on the TB where my idle seems best and left it. I also advanced the timing to 10 BTDC. I also took out the air foil in the TB to clean it and didn't put it back. Haven't driven the car but will post results in the morning. However, just from revving the engine, she still feels like there is too much of a delay between a hard rev and engine response. Almost like she is taking a gulp of air and sometimes a shake. The only reason it seems weird to me as when she is in open loop there is no delay, just a perfect response between a hard throttle and engine response. In open loop I can cruise in 2nd gear (manual transmission by the way) and when I stomp her she will break the tires loose but in closed loop I can't even break the tires loose in 1st gear. Will have to see how she responds on the road to these changes. So, now that I found out the TPS is within specs, any other ideas on what might cause my car to have a poor acceleration when I really try to stomp on her? I am going to have to just get a cable to connect my ALDL to my laptop and get a good scanning software to read my cars parameters. However, in the mean time, any ideas. To recap - replaced knock sensor, O2 sensor, TPS, IAC, plugs, wires, rotor, cap, coil, ECM, ICM, gaskets, and vacuum hoses. Also, I usually run 89 octane fuel and this morning I filled up with 93 (no choice between the two at my gas station near home) to see if there is a difference. The reason I did this was because a few years ago I accidentally filled up with regular instead of mid-grade and she had similar problems until I refilled with mid-grade. Plus, I thought mid-grade was 91 instead of 89, and I hate this damn corn fuel, LOL.

hassgrant

Motortrendz, I was posting my long response while you were posting your last, so to answer your post - my car is a SD with a MAP instead of a MAF. How do I check the ECM sense signal for voltage drop or high resistance? Are you talking about checking the signal to the TPS? Talk me through that one. I have replaced the O2 sensor twice just incase I got a bad one. Any other ideas? I appreciate your responses.

motortrendz

no problem, basically at the ecm connector you will need to back probe the signal wire, i dont have a schamatic in front of me for that car so i cant give you a pin or color, but basically you have 3 wires on the tps one is your 5v reference which goes out to all of your 3 wire sensors, your sensor ground and then your signal return to the ecm.. backprobe that wire with your red lead from your dmm, on the dc volt setting the black to ground you should see no more than .03 volts.. and you can do the same at the sensor.. if there is a high voltage drop that means you may have a bad wire, or ecm ground. depending where the drop occurs.. i hope that helps.. its so much easier to do than to explain..lol

do you have a scan tool where you can see sensor outputs? id like to see a koeo tps sweep on a scope, but honestly i dont like the readings seem too low, thats y i would do a voltage drop if you have high resistance within the wire you will bring the voltage down across the sensor bc the way it works is that if there is another load in series(high resistance) voltage will then split across both loads causing a faulty reading at the sensor..
ill give you an example incase its hard to understand, if i have a simple circuit with a power source a lightbulb and wires conecting positive and ground if you check volts before the light you will have 12v if you check it after the light you will have 0 v bc the load consumes it.. now if i add a second light of equal resistance if i check before the first light it will be 12v and after the first light will be 6v and then after the second light you will get a reading of 0.. you will always be able to add up the voltage drop in the circuit to get battery voltage.. so if the first light consumes 10v and the second light is alot smaller and has less resistance( like corrosion in a wire) you will see 2v drop there..
that is what i think is happening in your system... so check all your grounds and your signal wire

hassgrant

Motortrendz - ok I will try your suggestions. Unfortunately I do not have a scan tool at this time. If I am following you right, you want me to test voltage at the ECM and at the sensor itself and check for voltage loss. Is this correct? I think I did what you are explaining at the sensor and got .06V. However, I will check again tomorrow and get more accurate results. I do know that I am at least getting 5V from the ECM to the sensor, and that my sensor is now within specs for idle and WOT. It also appears that I am getting a smooth flow throughout the sensor from idle to WOT, but it is a digital VOM and it is difficult to know for sure. Now, can I test the wires at the ECM directly at the ECM under the passenger side dash, or do I check it in the egine bay? Keep the ideas coming please! In a previous post, I did post ohm readings across A and B, A and C, and B and C of the actual signal. Do they seem correct?

motortrendz

ohms dont give you a real accurate idea of what you have going on bc if you have just one good strand of wire and 20 strands broken your will test good on an ohm meter, but if you test it with a voltage drop you will see a huge drop, its like a 5 lane highway pinching down to one lane..

i would test it right at the ecm.. at the sensor you said you got .06(not bad) but if you test at ecm and its 0.01 you know its a .05v drop across the connector in the engin bay or in a wire, again not bad but not perfect. older systems are a little more tollerant of this.. newer stuff(meaning 2010.2011 cars would be thrown for a loop bc they are so sensitive now) but i think from your earlier post you said you got it better, so see if that works before you go nuts chasing wires.. remeber your not gonna get 5v out of the sensor, i believe max wot volts are abt 4.5ish so +/- .2 i think you will be fine.

hassgrant

The volts at WOT are within specification, so I am not worried there. I am now, since I tested the sensor with the correct VOM setting, beginning to think the TPS is not my issue. However, I just can't seem to grasp why in closed loop there is such a difference (open loop is great so I believe the car to be mechanically sound, just somewhere a sensor or the computer adjusts settings in closed loop and it affects the cars performance). I will add this little tidbit - In July, the car ran great after I found a torn vacuum line at the T that connects the line from my vacuum canister (oval ball in wheel well) to the cruise control and a cylindrical, triangular plastic piece that connects to the plenum next to the MAP (not sure of name). Anyway, once the car was running great, of course I was excited and I made a big mistake purchasing one of those $19.99 chips that splice into the wires that are attached to the IAT under the plenum. I followed all directions, and car was good. Well, one day, on way to softball, my driver side rim came off. I towed the car home and while I was waiting for my new rim to come, I was cleaning up engine bay and noticed the $19.99 chip had a slight melted plastic coming out of the plastic housing of the $19.99 chip. So, I decided to remove the chip and reset the computer. Well, the car has not run right since. This is why I replaced the ECM and ICM as I thought I might have damaged them with this cheap chip. Also, since my car is lowered, when the car came of teh flatbed tow truck, the tail pipes drug the ground - is it possible I damaged the exhaust system somehow? So, at this juncture is where I stand. Replacing sensors, chasing gremlins, etc., etc., etc. Any thoughts on this?

ASE doc

hassgrant, what is the inmput impedance of your VOM? It needs to be 10megaohms per volt for testing sensor circuits on a computer controlled vehicle. Your voltage readings changed when you changed scales because low impedance on the lower scale was pulling down the circuit signal. Most any quality DVOM will be 10M ohm/volt.

Diagnosis of TPS codes is done using a scan tool. The voltage test is only for glitches or drop outs. Looking at TPS voltage on a scan tool will tell you right away if your signal circuit is bad. With a scanner you can also look at integrator(short term) and block learn(long term) fuel correction.

motortrendz

did u damage the wire there? also when you are in open loop you are running full rich and the o2 sensors are not adjusting target or goal volts which tells the ecm to adjust pulse width to correct rich/lean.. thats part of y i said id like to see your long term fuel trim readings, i bet its way positive.. meaning its adding alot of fuel to try to correct a lean condition.. you would really only wanna see a +/- or 3 or less on long term to tell you its running correct..

motortrendz

doc you and i are on the same page.. i just didnt like the lower voltage readings when the tps was off the car made me think there was resistance in the return/sense wire.. but i think there is a fuel correction issue going on as well..

hassgrant

So what scan tool do you recommend? I have no way, right now, to test the things that are being recommended. Also, I am not throwing any codes, but I know that doesn't always mean anything. Suggest to me some scan tools so I can look into getting one. Again, thanks for all of your time and advice. Oh, in regards to damaging the IAT wire, no, I respliced the wire. Also, I have recently inspected my entire wire harness bundle to check for breaks or exposed wire and fixed some bad spots and rewrapped the bundle with heater hose to protect from rubbing and heat. I did this mainly because my speed sensor leads had rubbed through. Anyway, keep the ideas coming, I really appreciate it.

hassgrant

I also wanted to add that my EGR valve is a negative backpressure valve and is working and is only two months old. Also, the EGR solenoid is from a 91 Caprice 305 as I can not find an EGR solenoid for a 91 Z28 305 TPI. I checked to see if the solenoid was opening and closing properly and it was (was told you can test if it allows air through or not with the ALDL grounded and not and it did what was suggested, can't remember right now what was what). I have one question about the vacuum hook up for the EGR system - one port on solenoid has a copper fitting inside and one port does not. I currently have the port with the copper fitting connected to the small vacuum port at the bottom of the TB and the open port connected to the EGR valve. Is this correct? Also, (damn I have so many alsos, LOL), the vacuum line that goes from the charcoal canister to the passenger side of the TB used to be a small hard line. Well it broke and I replaced it with a single vacuum hose that is quite a bit larger than the broken hard line that was there. Is this ok? Just a thought incase that may be an issue. I am trying to put as much out there as possible. I have a feeling my issue is something simple that I am overlooking but something that someone else would say, well duh, there is your problem.

hassgrant

I want to add the following before I go to bed - is it possible that my issues may be caused by battery or alternator issues? Just wondering as sometimes my volts will drop (according to my dash guage) but my car never dies from lack of juice and then they will go back to normal. And the drain is not caused by the fans kicking on or anything, they just seem to fall a bit and then recover. I also had the alternator checked but it didn't give any readings. I only ask about the battery and alternator because I have learned over time that some things that you had no idea would affect something just might - for example, my car used to overheat bad and I couldn't figure out why. Turned out it was the radiator cap. I would not have even thought of that as it was not leaking or anything. I also notice that my oil pressure reads really low once the car warms up, I mean low enough that the pressure is just a bit above the red lines on my gauge. I also have some smoke coming from behind the passenger side valve cover. It isn't all the time, just sometimes and it seems to be smoke from oil. Just giving as much as I can here because this is the first thread I have started that I got continous responses to help me out. I thank all of you for your input.

hassgrant

Damn, one last thing I promise - I checked timing the other day thinking that was the issue and found she was at about 2 BTDC. So set timing to 6 BTDC (stock setting) and then played with timing to see what worked best. I found that 16 BTDC was the best but I am afraid of that advanced amount of timing. That is why I know have it at 10 BTDC and we will see how she runs tomorrow. Goodnight.

hassgrant

So, today, she started out so-so, and then she ran like a top with great throttle response and power. Then she would run so-so. I also noticed that my battery gauge would hop around alot. Sometimes like a fish nibbling on a line, and then sometimes would sway from 10 to 14. I unplugged the harness from my alternator while she was running and the volts dropped to 10 but stayed steady. She is also starting to hunt for idle again. Any thoughts? Bad alternator?

hassgrant

Well I tested my battery with engine off and it was just over 12 volts. I tested battery with engine running and it tested just over 14 volts. Thus, I assume my alternator is working. Now, if I can beat this damn idle hunting problem. As car idles for a bit it begins to lose RPMs and then surges to get back to 1000 RPMs according to my tach in the dash (I know they are not real accurate). I am not sure what is causing the idle issue lately. It sort of started after I replaced the plugs, wires, coil, cap, and rotor. I spaced the plugs .035 or .35, can't remember decimal place off top of head, and made sure plugs are securely attached to cap. The only thing I can't be 100% sure of is if the wires at the plugs are completely secure. I would have to say they are as I wouldn't half-*** put them on. However, I did not get under the car to check the passenger side wires. The driver side I can pretty much get to and they felt secure. So any ideas?

ASE doc

The fluctuating voltage is not helping your ECM. It has a built in voltage regulator that can maintain 12v on anywhere between 11 and 15v. When you drop to 10 its being starved for power. Closed loop on these cars is fairly simple. The one thing that really comes into play in closed loop is the O2 sensor. During open loop, the ECM monitors O2 voltage but does not make corrections based on it. When the ECM sees the O2 sensor begin to read AFR, showing that its at operating temperature, it switches to closed loop.

BLM and Integrator are the ECM's long and short term fuel correction maps. These do not function in open loop. In open loop the ECM runs completely off of its own base fuel map. Your speed density system does make corrections for coolant/air temp, TPS, and load while in open loop. If your car were a MAF car, the ECM would follow the MAF in open loop.

The fact that your car runs well in open loop means that its basic fuel system and engine sensors are working properly. The fact that it goes south in closed loop makes me wonder how healthy your O2 sensor is. As far as a scan tool goes, there are several that are availble fairly cheap and work well on these cars. Basically any scanner that reads OBDI and has the interface for the 12 pin GM ALDL will work. One good option is the Snap On MT2500. Theyre cheap used and are very durable.

hassgrant

The O2 sensor is new, within the last month, month-and-a-half. Is there a good way to test the O2 sensor? Today, she had her moments where she ran great, and then others where she ran so-so. ASE doc, would something like TunerPro work for my situation? I have a laptop, and buying the ALDL cable is much cheaper than $250 for the SnapOn MT2500. Well I am off to play softball, curious to see how she will run.

hassgrant

Real quick - any idea why I am having so much trouble trying to do minimum air setting? That may not be right name of process, but it is the process of getting vehicle to operating temperature, turn of engine, jump A and B of the ALDL, turn ignition to on, wait at least 30 seconds, disconnect IAC connector, remove ALDL jumper, start engine, set idle by adjusting screw on side of TB. I have seen some that say to disconnect the timing plug (EST I think it is called) and some don't mention it. Anyway, when I try this, my car will not keep a steady enough idle to adjust properly and it usually dies unless I set the idle way up.

hassgrant

Well, first off we won the championship for the season with 14 runs in the top of the fifth. Now, to more important stuff - car ran pretty good tonight, no weird voltage issues, only hunting idle from 750 RPMs to about 900 RPMs according to tach in dash after about 30 seconds of idling. Not sure what is the issue there. I do know that one time I gave her a little gas and as she came down she didn't recover and died. But anyway, she is driving better, not 100%, but probably about 85% if I had to guess. If I could get her to idle steady I would be happy. Keep the ideas coming and I will keep you posted.

90firebird

Just a quick thought:

Are your IAC ports all cleaned out? Gunk that has accumulated in there could definitely be contributing to your idling issues...

hassgrant

I cleaned them when I replaced the IAC the other week. The car is running pretty good now, except I now have a leaky injector. Will have to fix that tomorrow.

PurpleG20305TPI

I know this is old, but i would like to know if i have a 12v wire brn/white wire that i think is for the SES(if i ground the wire, the ses comes on) Could i damage my ecm if i wire that to the ses at the ecm. so 12v will be going into pin A7 i think...Is it bad to put 12v to the ecm?

afremont

NEVER apply 12V directly to any of the regular sensor inputs (temp, map, tps etc). The actual input needs to always be between the +5V the ECM supplies to the sensor and ground.

That said, it sounds like you've found the wire coming from the SES light in the dash, as brn/wht would be the right color and, grounding it would turn the light on. You should be able to safely connect this wire to the SES pin of the ECM since it grounds the connection when it wants the light on. This sounds like the right wire and yes it would appear to have 12V on it when you put a meter on it. A test light might not turn on though as the current will be limited by the SES bulb when it illuminates.

PurpleG20305TPI

AWESOME!! you actually answered another question i had about none of my sensor, tps, map etc, arent getting 5v in the on position. but i tested it with the multimeter neg lead to the battery, and the red probe to the Red wire thats supposed to have 5v. so i think i might have tested it wrong. i think you prob the black wire and the red, not battery and red. at that point they should have 5v constant? or varying depending on what the ecu puts out? ie, tps varying volts based on the position of the sensor. correct?

Just to be 100% clear, i CAN wire that ses wire to the ses pin at the ecm? the 12v going into the ecm wont harm it?
Thank you so much for your assistance.
Dean :-)

afremont

When everything is connected, the battery negative should be at the same ground level potential as the ground lead of the sensor wiring, but it grounds thru the ECM. You should certainly have 5V between the 5V(red?) wire of the sensor connector and the ground wire of the connector.

Yes, you should be safe hooking that wire to the ECM since the bulb is in line. Don't just hook another 12V wire to the SES pin or it will probably destroy the driver transistor in the ECM when it shorts the 12V to ground. The bulb limits the current to a safe level.

PurpleG20305TPI

Wonderful. now i can check my codes and hopefully have her running SOON :-D youve made my night. thank you.
Dean

Ltnascar

I have a 86 2.8 multiparty I have had for 35 years. If my tps will not go high enough in voltage n mine is .54. I Lower my Idle.I hope it might help in some way