wgripp

iTrader: (1)

Right now my '91 GTA is in the shop for a surging at idle. L98, TPI, 350

Apparently, the engine is also only operating in "open loop" and won't go into "closed loop." The surge only happens after the engine is warmed up. The mechanic just replaced the valve seals. (This problem existed BEFORE he replaced the valve seals.) He also cleaned the IAC valve and the throttle body. With the engine in "open loop," it is not throwing any codes. Any thoughts?

Thanks!
Bill

Schrade

Average mechanics can't detect vacuum leaks very well:
Max injector pulsewidth (in Open Loop) will foul cats in short order. Keep driving to a MINIMUM until diagnosed...

wgripp

iTrader: (1)

Brother,

Thanks for the write up. Two questions...

1) I'm not getting a code. Does that mean it's not a vaccum leak?

2) Won't spraying starting fluid everywhere foul up my under-hood plastics?

vetteoz

iTrader: (13)

Would be better if you started your own thread instead of hijacking someone else's.

Have you done the obvious and pulled the engine codes to see if anything showing ?

https://www.thirdgen.org/forums/tech...s-dumbies.html

vetteoz

iTrader: (13)

A code is only for a problem " seen" by the ECM on one of it's inputs.

There are many " mechanical" faults ( like a vac leak ) that would not necessarily cause a code to be generated unless it upset the parameters expected by the ECM

How do you know?

wgripp

iTrader: (1)

I'm tracking with you on the lack of a code being thrown.

I know the engine is stuck in open loop because my mechanic's ECM scan tool says so.

Does anyone know of a way to test for a vaccum leak that does not involve spraying starter fluid everywhere? I know from past experience that it will discolor some of my underhood plastics.

Why would a vaccum leak prevent an ECM from going into closed loop?

Are there any other possible causes of this problem besides a vaccum leak?

watajob

iTrader: (29)

Use propane or WD-40.

wgripp

iTrader: (1)

That's a good idea. They seem like they'd be plastic safe!

joewilly

Well I am new on this site but when I need any advice from you I will ask.

So **** off

wgripp

iTrader: (1)

well, my mechanic thinks that the problem is probably not a vaccum leak. Any other thoughts?

five7kid

iTrader: (14)

Well, take some advice from me, then.

The Board Terms of Use, to which you agreed when signing up, and the Message Board Rule posted at the top of every forum, say you don't use language like you just did, and that you don't post off-topic from the original thread topic.

So, you can accept the friendly advice which was offered to you with no ill intent, or you can take a little involuntary break from thirdgen.org. Your choice.

Schrade

Not likely that starting fluid will stain plastic.

The vapor pressure of starting fluid (that's how quickly it turns to vapor, from liquid), is EXTREMELY higher than gasoline - that's why it's used as 'starting' fluid.

And not likely that a vac leak alone will keep the ECM in Open Loop. Only a DTC Code, I think, will keep it in Open Loop. But lots of time with loping idle FROM a vac leak WILL foul the O2's.

Once the exhaust is fouled from unburned gas / HC's, the O2's and cats included, it will could stay in OL.

vetteoz

iTrader: (13)

So if he has a scan tool on it he should be able to see if the O2 sensor is cycling correctly which is a major decider for the ECM going into CL along with correct indicated engine temp

wgripp

iTrader: (1)

I have an SLP cold air intake. The hard plastic of the cold air intake attaches to an "accordion" looking funnel which attaches to the throttle body. Starting fluid once turned this white. I had to rip it apart and clean it up.

What do you think is the cause of my idle and open loop woes?

wgripp

iTrader: (1)

I will call and ask if the O2 sensor was cycling correctly.

wgripp

iTrader: (1)

Called the mechanic. He said the O2 sensor wasn't doing anything. Does this mean I need a new O2 sensor?

Schrade

Up front answer? NO!

That's a BS answer from the mechanic. You want to know if he still has the printout, showing the readings of the O2 in millivolts.

No millivolts = DTC [bad O2]

Forget his WORDS. Words go away when the sound stops. Your cash often follows the sound, but the echo effect is never as good.

You tell him that you're from Missouri (Show ME), and you need to see that they're not doing anything.

Schrade

SLP? Like ... with re-usable, oil-able filter elements???

Do you have MAF in your TPI? Or MAP?

If MAF, and too much oil on the air filters, it will pull onto, and foul, the MAF FILAMENT. FOULED MAF = GREAT ECM UGLINESS!!!

If you're on MAP, oil can still foul stuff, like plugs...

SHERLOCK the wrench OUT

vetteoz

iTrader: (13)

As the man said ;if the ECM is not seeing anything from the O2 then it should have a code up

A code means the ECM has seen a fault somewhere in a system; could be a bad connection , ground or power supply.
Not just that the item of that circuit is faulty
There are diagnostic charts in the factory service manuals ( best investment you will make ) to work through to identify the ACTUAL problem
before throwing $$$ at un-needed new parts
See
http://www.chevythunder.com/o2_sensor_diagnostics.htm

wgripp

iTrader: (1)

What does DTC stand for? So as long as I'm getting some millivolts from the O2 sensor in open loop, it isn't bad?

wgripp

iTrader: (1)

The ECM isn't throwing codes. I have a service manual, but can't find it. Does anyone have scans from a '91?

wgripp

iTrader: (1)

Schrade, you may be on to something!

Yes, that's my cold air intake. Yes, I over-lubed the crap out of it a few years ago when I was cleaning it.

I have a '91. Is that MAP or MAF? If I have MAF, can the filament be cleaned, or do I need a replacement? Will a bad MAF throw an ECM code? Can the filament be tested to see if its still good?

On a side note, the mechanic says its running lean in open loop.

Schrade

The MAF filament is DELICATE. CLEANING IS TEDIOUS, TO NOT DAMAGE IT. USE A TINY PAINTBRUSH, CAREFULLY, IF MAF, AND NOT MAP...

I DO NOT KNOW WHICH IT IS

wgripp

iTrader: (1)

I think 90-92 cars were speed density. I think that's MAP.

Schrade

Excess air filter oil MIGHT still foul the MAP sensor.

Only way to check it is by the mechanic's scan (voltage), or visually...

wgripp

iTrader: (1)

What should the voltage read for the MAP sensor and the O2 sensor?

novaderrik

maybe you mentioned it and i missed it, but you checked the temp sender and the wires going to it, right?

vetteoz

iTrader: (13)

All documented in your FSM ( when you find it )
The O2 checking values are in the link I posted for you above, did you read it ???

Depends.
A correctly functioning O2 will have a wildly swing Mv output , not a fixed value

vetteoz

iTrader: (13)

Diagnostic Trouble Codes

The thing that tells you what is wrong with your engine

vetteoz

iTrader: (13)

If as you say there is no output from the O2 sensor showing on his scanner, how would he know?????

Yes , the same DTC as for a MAP fault

vetteoz

iTrader: (13)

Time you learnt about your car.

TPI MAF engines have the MAF sensor on the intake ducting in front of the TB; your '91 doesn't so it would be MAP ?

wgripp

iTrader: (1)

Nope, no sensor in the ducting in front of the TPI. It's MAP

wgripp

iTrader: (1)

Gents,

Thanks for all your help so far! I really appreciate it!

Bill

Schrade

MAP voltage, and O2 voltages will be different, depending on conditions. Supply voltage to each one is either 5V, or 12V.

The voltage (signal) that goes BACK to the ECM, as a result of the varying manifold pressure, or varying amount of elemental Oxygen in the exhaust, should fall within a range, which is detailed in the FSM.

When it goes out of the range, the computer registers it as DTC 'X' - MAP is 34(?), O2's are in the 60's. C Current DTC 'X' (caught in the act), or H History DTC 'X' (hide and seek)(sucks too!).

The problems don't go away by themselves either, just because the light is out. That's a H DTC. Will probably light up when it warms up Closed Loop.

You really need FSM to maintain a car, or lots of cash for lousy or unscrupulous hacks. Navigating it - it's HUGE, is a pain. But knowledge goes further than cash. Always. And it makes you a better communicator, and problem solver too.

For starters, get a scan printout from a mechanic. Might have to pay a few $$, but they can't lie to you when something is on paper.

wgripp

iTrader: (1)

Ugh, I'm in the military and I've moved a bunch of times. I can't find my manual for the life of me!

wgripp

iTrader: (1)

How can I accomplish this?

wgripp

iTrader: (1)

Allright,

This thing is turning into a disaster.

I spent quite a bit of time this morning digging through boxes, tearing up my attic, etc. I cannot find my service manual for the life of me.

I had dual cats from the factory and a flowmaster 3-inch cat-back exhaust. In order to install my Spohn torque arm (with drive shaft safety loop), my mechanic had to cut a section out of my exhaust. He cut behind the cats and he cut after the y-pipe.

After installing the torque arm, I limped my car to the exhaust shop to have the cut-out section re-welded in. I drove slow, and it was LOUD. But I didn't notice any problems.

I picked up my car from the exhaust shop today. He couldn't save the y-pipe. I paid $156 to have a new one fabbed/welded in. He used 2 1/4 or 2 1/2 inch pipe (the same diameter as the piping before the cats) to replace the cut out section. It seems narrower to me than what was cut off the car. Furthermore, he said all the shops in town use crush benders (not mandrel benders). Ugh. So, I had to settle for crush-bent pipe.

After paying for the repair, he told me the car was shaking at idle. Originally he thought the new exhaust piping he installed was hitting the torque arm (or something like that). But, he put it up on the lift and didn't see anything wrong. After talking, we assumed this was just a symptom of the newer, firmer, crossmember/torque arm/poly urethane trans bushing plus my new Koni yellow shocks up front.

Sure enough, after driving off, I noticed two things. One, the exhaust seemed louder. Two, the idle seemed rougher. Again, I assumed this was a symptom of my new performance parts. Once, I tried to floor the gas pedal from a roll to test my new torque arm. My car didn't respond. It raised an eyebrow. But, I let it go.

Up to this point, I hadn't gone faster than say, 45 mph. I drove the car to a gas station and filled her up. When I tryed to depart the gas station, I couldn't get the car to start. I had to hit the gas pedal while turning the key to get her started. Then, we got on the highway. The car was *******. At first, I couldn't get her past 1.5K RPMS. Then, I couldn't get her past 2.5K RPMS. Then, I couldn't get her past 2K RPMS. At some point during this ordeal, the SES light came on (somewhat briefly) and then turned off. (The light was off for the majority of the time.) I got off the highway, and the car kept dying on me at stoplights. Then, I got her in my driveway and turned her off.

I went inside for several minutes, then came out to put her in the garage. I cranked the motor, but it wouldn't start again. I cranked it and gave it gas, but it still wouldn't start. This went on and on to the point where I thought I would burn out my starter, and I still couldn't start the motor. Then, I let her sit for a few minutes, and was able to start her up and get her in the garage.

Does anyone have ANY idea as to what is causing these issues? I'm afraid that driving her to the mechanic will damage my engine internals!

The worst part is, I'm about to go on a little trip. I don't want the car sitting around and not getting used. That's what dried out my valve seals. It just cost me about $550 to have them repaired! I wanted to be able to let my wife start her up and drive her around while I was gone to keep her working.

Schrade

The mechanic should not have done ANYthing except to diagnose the Stuck Open Loop problem.

SES light going out means the problem is still there. Rest assured.

Temp Coolant Sensor could keep it in Open Loop. But no need to check it yet.

Get it plugged in for codes - somewhere ELSE. Get a printout of the codes.

Diagnostics for codes often defer to another code FIRST. They have a way of compounding. Once you get the codes, either get the Factory Shop Manual, or an online subscription to Mitchell's Online, or AllData (online). You might get a trial subscription for 30 days with one of them...

wgripp

iTrader: (1)

He installed the parts at my request. I was trying to get as much work completed as possible before taking my trip. But, I'm really worried they went with too narrow pipe on my exhaust system, robbing me of power.

Is there a scan tool with all features I can buy for a reasonable price?

Schrade

I don't understand mods before tune / diagnostics.

Open Loop keeps injectors at max pulsewidth, and the exhaust is gonna' Carbon-foul with excess hydrocarbons and unburned fuel.

Scantool? Tech1 for $250, if you're lucky. Scan software with hardwire connector - $70, with free trial period, and lots of time to learn navigation (I'm doing that now with the ZR-1). No picnic either.

Or a super high-tech code puller:

Jump pins A + G on ALDL. Read SES flashes. You still need FSM to start diags. No fun, but you have to do it.

Tuned Performance

iTrader: (92)

G ground your fuel pump Try B
OL does not keep the injectors at full duty cycle but does not use o2 correction due to lack of o2 swing and ect below 146F.
Tunerpro is free

Schrade

You can sure as Hell get input finally, if you make a mistake.


Just tell OP what to do to fix the problem. Forget about TOPhack's mistake.

joewilly

For the moderator, You know I am 77 years old with some time in the USMC.
I mentioned I was new on the site and nowhere when I pull up my screen is there any
place for me to start a thread.]

So it looks like you are not doing your job.

I have no further interest in this site so kill my pass word and the gibberish I see
can continue.

wgripp

iTrader: (1)

I'll be purchasing either this

http://www.reddevilriver.com/ALDL_Bluetooth.php

or this

http://www.reddevilriver.com/aldl.html

shortly.

I like the idea of the traditional cable because it's a tried and true method. However, the bluetooth cable would let me pull OBD1 codes with my android phone, once the app is finished. But, I'm worried that if I get the bluetooth cable, I'll have issues getting the software to work correctly on my computer. (I forsee driver and connectivity issues.) (Yes, my laptop has bluetooth.)

What software do you guys reccomend?

jmpowie

I would say he going back to H.A.M.B

wgripp

iTrader: (1)

New mechanic diagnosed my problems as bad O2 sensor and bad fuel injector. I will be replacing all the fuel injectors and the sensor soon.

Thanks