tooltime

Hey guys, I need some help with a 91 rs convertible. My son and I went to look at it, it would barely start, we shot some carb throttle body cleaner and some sea foam in it and it would back fire run for a bit and then just peter out. Got a couple back fires with some impressive flames but no joy on keeping it running without spraying the crap out of it. I have an 83, this 91 has dual injectors with butterflys....not sure if it's TBI or TPI????? I just want to get it running to test drive the car. Sea foam sucked into the booster pump hose? Let it soak or pull the carb and clean it out. The injectors are pumping fuel, it has a new fuel pump, it will run if you feed some cleaner in it as your cranking, and it will limp along for a bit before it just dies. The car has sat for a while, I threw a 1/2 can of foam in the tank as well. I suspect bad gas, varnished throttle body, because of the slight sticking sound at first movement of the butterflys, an it has most likely sat for longer than what I've been told. The car is nice, but I need to drive it before I make my mind up on it. Any help would be greatly appreciated. Thanks Matt

RS-Chevy-SS

1) check fuel pressure

tooltime

Is there an easy way to check this. I will need to disconnect the line right at the carb/injector correct?

RFmaster

1) Tooltime you have Model 220 TBI - it is not TPI
2) To check pressure you can rent a fuel pressure kit from local parts store or purchase Actron CP7817 fuel pressure gauge with TBI adapter kit. The easiest place to check Fuel pressure (FP) is by inserting TBI adapter fitting right where flexible fuel hose mates into hardline mounted on the intake (back side of alternator). There are two fuel lines: supply and return. The supply is larger of the two - this where you need to insert the adapter gauge. Spec is 9 to 13 PSI. More than likely you'll see 2 to 4 PSI.

//RF

Spaceboy1980

iTrader: (6)

If it is the pump you must almost completely remove the differential, drop the exhaust, remove two heat shields, then you can access the tank. It sucks.

tooltime

New fuel pump. I'm thinking old gas, maybe plugged filter, TBI could be totally gummed up. Would sucking some sea foam into the booster pump hose help clean out the carb? I know that it will get rid of misquitos. Just trying to get it running. I can go through the carb at a later time. I am getting gas shooting out of the injectors, I just need to check pressure. going to advanced tonight to get a gauge to check it. I'll report back what I find. Thanks guys.

RS-Chevy-SS

No, the booster runs straight to the runner on stock cars IIRC. Check pressure and go from there.

tooltime

Alright race fans. Here is what I found. I soaked seafoam in the butterflys from two days ago. There is still some varnish that is sticking the butterflys a bit. I pulled the upper housing off the carb that holds the fuel regulator. All the passages are clean, the regulator was new. I blew some cleaner though all the ports on the carb base, where the hoses hooked up to the base of the carb to make sure that there weren't any obstructions. So. Trying to crank over the car, the car would bog down as you opened up the throttles. It would try to start as you took your foot off the gas and bog down again as you opened the throttle again. I could get it to start to fire just a touch, backfire and then catch all the fluids on fire as the back fire went into the engine compartment. There were a couple of tense moments. I about **** my pants. Seeing how this isn't my car yet. Watching the injectors or whatever they are called, that hang over the ports of the carb. They would shoot blasts of gas, on and off, faster as the engine started to jump to life and then slow back as it bogged back down again. So I have fuel, I checked spark, I pulled the #1 plug and cranked the car over. The car has new cap, rotor, wires, plugs, three sensors on the TBI. Not sure what they are, but they are new. New fuel pump and filter. Help help help. I can't for the life of me see what's the matter. Fuel, air, fire. Sometimes too much fire!!!! I did see that he had put the #4 and #6 wires on reversed, I think. I couldn't access anything on the fire sequense and cap layout on this car. Where can I find it. I'll look as soon as I post this and try to see if I can find some more posts like mine. Any help would be great. Trying to get this one back to life. Thanks Matt p.s. the coil is new as well

mauijerky

From your first post, you make it sound like lack of fuel. "no joy on keeping it running without spraying the crap out of it." Although, you seem confident that the fuel system is working. "New pump and visible spray coming from injectors." The backfires do indicate a potential ignition timing issue. I'd say you're on the right track by checking the firing order. It's 18436572. Should be casted on the intake manifold. The best way to confirm proper firing sequence would be to set the motor to top dead center and observe which tower on the cap that the rotor is pointing to. This is where the #1 wire should go. It should be on the front side of the cap pointing towards the motor. If the rotor is pointing towards the firewall then the motor is not at TDC. After confirming the #1 location, then just follow the firing order around the cap in a clockwise pattern. The next tower to the left of #1 will be #8 then #4 after that and so on. Make sure you follow each wire to the correct cylinder.

Don't worry about the sticky butterflies or trying to seafoam the intake right now. These are not things that keep a motor from running.

tooltime

I'm with you on the timing issue. It was my next thing to look at. I spent so much time and effort on the damn carb, that I was spent. I looked at the cap, but didn't take the top off, to see if the rotor was pointed in the correct position. The owner of the car said that the guy that replaced the fuel pump and filter tested it by turning on the car with the fuel line off after the filter and he said that it shot gas accross the drive......So you know it was working. My worry is the line to the carb might be rusted, plugged, who knows, but even with the ammount of gas shooting while turning over the car, we should have gotten it to fire run and stall out with low gas pressure.....am I correct in assuming this? The next issue is spark and timing. He replaced the coil pack and rotor and cap. If he did this wrong, I'm screwed there as well. I can see the nut and retainer that holds the lower gear that holds the location of the cap gear, which sets your advance or retard on your timing. It hasn't been touched in years, due to the ammount of crud and debris on it. So he could have put the rotor in backwards, unless it is installed in only one way. I'll double check the caps wires and location of the plugs, but from what was just posted, it looks correct. Let me know if there is any idiot test out there left to do, because, that's about what I am beginning to feel like here. Seems like I'm missing something here but cannot put my finger on it. I tried to read post last night but they are far and too inbetween. ICM's TBI's.....I have fire, spark, and air. What are the wired controllers that are in the passenger side of the base of the TBI. Throttle positions switch??? Choke? Gas shut off? All three are new, the wire harness have no retainer clips, but the wires are secure in them. I checked!!! So, I'll check pressure, and check Top dead on the number one and rotor position. Thanks again for the advice. Matt

RFmaster

Tooltime

We've to send you to re-education camp. All this 'carb' stuff should be left where it belongs. Yes, there is a learning curve, but in retrospect EFI (which TBI is) is far superior for every day vehicle. To start your re-education you have a homework assignment. Read the following thread:

https://www.thirdgen.org/forums/tbi/...check-out.html

After reading your postings it would appear that you're getting fuel into your engine. That means that dizzy is sending DRP to ECM which in turn actuates injectors. Since the engine is 'burping' that indicates that you have fuel reaching combustion chambers and spark to light things up. Base timing and engine compression are questionable. I would make sure that compression stroke on #1 Cylinder corresponds to dizzy pointing against #1 cylinder post position.

a) There is no throttle position switch in GM TBI system (Nissan, Mazda and Toyota and others do have them) - there is a TPS bolted on the passenger side of the TB. TPS = throttle position sensor provides ECM with a continuous indication of throttle position from full close, it idle, to WOT. It is a potentiometer (a variable resistor) and it provides a voltage variation sensed by ECM (range 0.7 to 4.5VDc)

b) There is no Choke. Instead there's Idle Air Controller (IAC) located on the passenger side at 11:00 o'clock position, which controls amount of air bypassing throttle plates. This is a multi purpose actuator (it is a dual coil stepper motor), but most often it is used to control idle speed.

//RF

tooltime

Ok, I read my homework. Interesting, but still. I need help trouble shooting the TBI not how to update it. There wasn't one thing in that thread that really helped me out at all. I understand most of it. I really just want to know if there are some ways to check if these componets are working. I'm not trying to sound like a smart ***. The car will not start, stumble or even disel on. I admit, I need to check fuel pressure, but even with a small amount of gas that shots out of the injectors, it would run. Timing, if it was off just a touch, it would run like crap, but still run. New coil, cap,wires, and plugs. Even gapped incorrectly, it would run like crap, but still run. Reading that post didn't help me get the car running, it show me how to muscle up my 305 TBI. I'd be happy with a limping car right not. Between the gas pressure, IAC,TPS,and the ECM. Which was never explained in that post, someone out there has to know how to tell me how to trouble shoot these. We'd all have new parts on our cars if we just threw stuff at them. Can you pull the TPS off the carb, hook it back up to it's wire harness and see if it work or not. IAC. Can it be removed and tested with the car or does it have to be bench tested with a volt meter. I'm racking my brains out, I've looked at the basics here can't get anything to help here. I hate to see this car just sit. They get worse the longer they don't get used. Let me know. I'll keep reading on some trouble shooting to see if anything helps. Matt

tooltime

What is the ECM and ICM Same different? Ignition controll mod and what??

RFmaster

Matt

a) Checking TPS by itself - removed from TB (lets be clear - it is not a cab since there is no venturi) or even if TPS installed on TB.

Parts identification below



Since you have '91 you have a late model TPS like the one in the photo above. To verify TPS functionality requires DVM. If you can get pig tail from Junk yard (like it is shown in the photo) measuring TPS resistance between its terminal is much easier. Poking inside socket well is a royal PITA while trying to get a good contact. If you get a pig tail measure resistance between pins A & C (Gray and black) should be around 6 kOhm, pins C and B (black and blue ) will vary depending on throttle shaft position from about 1 kOhm to about 6.5 kOhm.

2) IAC = Idle air Controller. It is best to leave it bolted to TB. The way to verify if it is functional is force ECM into diagnostic mode by jumping Pins A & B of ALDL plug located on driver side. With ignition on ECM will force IAC into a fully extended position. You'll hear IAC click continuously while the jumper is in (while ignition key is in run position). You should see IAC pinticle head protruding through the air by pass orifice just above TB attachment bolt (11 o'clock).

3) ECM = electronic control module. This is a computer which monitors and controls EFI functions

4) ICM = Ignition control module. This part is mounted inside dizzy and provide points functionality.


//RF

tooltime

Got it. Thanks. I have an 83. Carb car. Hard to break old habbits. I know that the TBI is a different beast. Thanks for the lesson on the ECM and ICM. Trying to decide what will be the next best line of attack would be. I want to pull the cap and check the dizzy and make sure it's correct. I believe it is. I've been watching videos on youtube on some other TBI issues. Looks like my injectors are kinda down on pressure doesn't seem to have quite the spray and mist like it should kinda dribbles and spits. Now I'm leaning back to fuel pressure. I'll get a gauge and check it.

tooltime

Can you think of anything else that could be the issue here. I'm spent!

mauijerky

tooltime,

So now it stays running but rough? Does it still backfire through the tbi? Backfiring is a sure sign of something out of order in the ignition.

Did you try shorting the ALDL connector and checking for any trouble codes?

https://www.thirdgen.org/service-eng...ht-error-codes

How's the vacuum line going to the MAP sensor? The stock hose is made of hard nylon which can get brittle and crumble after so many years.

Data logging would be nice, as it lets you see all the sensor data in real time. This would give you a better idea of a sensor fault. But, you need an ALDL usb cable and a laptop. The MAP sensor, TPS, and coolant temp sensor are the ones that might mess with first startup of motor.

Did you take the cap off and verify #1 location and follow the firing order around the cap?

You can pull off the ICM in the dizzy and bring to your local auto parts store to have it tested. Maybe give 'em a call first to make sure the service is offered.

If the ignition system checks out, then focus on fuel. Either a faulty sensor is causing improper injector pulses or the incorrect amount of fuel is being delivered to the injectors.

Did you install the new pump or were you just told its new? If the car has been sitting, then how long ago was this "new" pump put in? That being said, usually the pumps works or it doesn't. The rubber line that connects the pump to the hanger could be loose or punctured.

Is this your car or you thinking about buying it? I say, no matter what its fixable. I went through all kinds of hell with my '91. But I learned a ton along the way. Majority of my solutions I found just searching the archives of this site. I say you have two options....either take on the challenge of learning the GM TBI system or just convert it to a carb if they are easier for you to work on. Either way, you'll get the car running good!

mauijerky

My preferred method to search this site is with google. In the search just type what you want to look for followed by site:thirdgen.org. For example, I did a search for "tbi test site:thirdgen.org" and the first link was this:

https://www.thirdgen.org/forums/tbi/...ing-101-a.html

tooltime

No this car is not alive at all. It won't even fart without some sort of cleaner, or starting fluid shot into the TBI. I can watch the gas shoot out of the injectors as my son turns it over, but on it's own......dead duck!!! Yes I was just told it's a new pump. This guy is a 71 year old man, great guy,he's just as frustrated at the car as I am. He has been throwing parts at the problem and has health issues and cannot work on the car at all. I'd love to buy it, but would love to hear it run, shift, and check out the car as it should be. There could be other things that you don't know about until you road test a car. I've been bit too many time. I'm going to try to go to one of the box stores and see if they have the TBI Fuel pressure gauge to install on the car. If not, I was going to unhook the gas line and key the ignition to see how the pressure looks at the TBI. Then I was going to try checking the TPS. Then check for proper alignment of the rotor. I have, or HAD, a book on my 83, I can't remember if it covered the 91 or not. The garage will never look the same, or the house for that matter. I have gone threw it all and cannot find it. Time to maybe buy a new one. Trying to get over to the car today. I'll post my findings. Matt........Thanks for all the help and advice.....I'm trying to pick it up as fast as I can.

RS-Chevy-SS

So we don't know for sure when this pump was replaced? I like to rule out fuel pressure before everything else since it's so common. It doesn't take very much sitting time for the house between the pump and lines to go out

RFmaster

I understand your frustrations all too well, but to overcome this a methodical approach is required.

a) The fact that injectors are pulsing during cranking indicates that ECM is receiving DRP signal from dizzy and ECM in turn commanding injectors to pulse. So this in itself tells me that distributor parts and ECM are alive (to a degree). Just make sure that you do not security light turning on in your instrument cluster. VATS issue can be easily overlooked (you have '91).

b) I would make sure that I get solid spark during cranking. A spark plug tester is very handy. You must have ignition system (reluctor coil, coil, dizzy cap, rotor, plug wires, and plugs) that consistently provides spark. This also requires a fresh battery and a maintenance charger. Needless to say correct spark plug wire routing to corresponding cylinders should be verified. Plugs must be clean and dry.

c) Fuel pressure verification is an absolute must. No way around this, especially for a car that sat for a long time or have questionable gas in the fuel tank. Purge old gas from the gas tank - that stuff is nasty! With fresh gas you must have solid fuel pressure during cranking (and running) - factory spec 9 to 13 PSI.

Once you cover above basics it should start showing life signs - at least a burp or two. Keep us posted and what ever you do not give up. Just walk away from it for a short period of time and think the problem through. Just remember - you're not the first (nor the last) person that have faced the same problem.

//RF

Schurkey

First Two Guesses: Old gasoline that won't vaporize and hardly burns, and fouled spark plugs.

tooltime

Hey guys, I haven't had any time to work on that car for a bit. I also have'nt had any luck finding that actron cp7818 TBI fuel tester. Question. Do you cut the rubber line, install the T adpter and leave it in there or what? Looks like most of the fuel pressure testers are screwed into a shrader valve hook up or this hose clamped T adpter. Guys at the stores are either younger than the car that I want to test and have no clue. Jacking with the fuel line feels wrong, but it that's my only option, that's what I'll do. Can you undo the fuel line to the TBI and hook it up to the end of the line as well? Anyway, that's all I have to report for now. Thanks again for your help, hope to start again this weekend on it. Matt

RFmaster

Ebay has them - CP7817 kit has TBI specific T tap: 351133891036 with free shipping for $30 can beat that.

//RF

Schurkey

Wrong unit. You're looking for the 7817, not the 7818.


Comes with a TBI-specific gauge (low-pressure) and thread size. Also comes with a pressure tap that threads into the back of the TBI unit.

This WILL NOT work on some van applications. There's no room behind the TBI unit to screw the pressure adapter into place. Works fine on my K1500, and probably works fine on F-body. The pressure adapter is not left on the vehicle in most cases, it's removed when the pressure test is completed.

Another possibility is to replace the fuel filter with a pressure adapter. It's the only choice for a van, optional on other applications. The adapter is silly expensive, and I don't understand why.





You have to be careful about TBI pressure guages and adapters, they sometimes but not always use a different thread size or connector style. A TBI gauge assembly may not thread to a TBI pressure adapter, and/or a regular fuel injection pressure gauge may not thread to a TBI pressure adapter. Some even use quick-couplers.

tooltime

I found one at Auto Zone. I'll try it this weekend. The guy went out and bought a new/used TBI for the car off a froze engine. Still won't run. I'll post tomorrow night after I work on it. Thanks Matt