topfile

Daughter says her 91 Z28 305 TPI just not running like it use too. Stalled
in traffic and had to towed it to the shop. Mechanic replaced the module
and coil and still does the same thing. Car has 200k on the engine i think.

It had a little smoke last year but that was fixed after valve stem seals were replaced.

Code 32 EGR been setting code for some time not a big deal. Mechanic reported the new code 42.

Symptoms;

-Stalls after about 3 miles of driving
-Must sit and cool for about an hour and then restarts
-Missing on 6 and 8, pulling these plug wires and it runs the same
-Has spark on 6 and 8
-Plugs don't look fouled
-code 42 and 32 set
-Fuel pressure checked and good


Actions taken;

- replaced intition coil and module
- plug wiring order was verified
-Fuel pressure checked and OK'd


Still having the same trouble any ideas?

five7kid

iTrader: (14)

Did you check the fuel pressure when it wasn't starting?

ntomsheck

iTrader: (1)

Do a compression check, and test your pickup coil.

topfile

My mechanic confirmed the it was OK a few days ago as he suspected the fuel pump
just as you did. The car starts fine when cool. Therefore, I'm sure it was running
when he checked it. The previous owner indicated the fuel filter and pump are relatively new.

Thanks for your input. Something else?

topfile

The pick coil is no more than 1 year old. Mechanic is pulling distributor and I'm sure he check it again. The old one although burnt to crisp still tested good last year but I replaced it anyway while I was into it.

In regards to compression..He said #6 was at 75 but would test # 8 soon.

Pairof91rss

Check the resistance on the injectors (cold, and hot) My guess is they need replaced. Injectors should be around 16 ohms. Mine did the same thing, and the driver side injectors all read less than 9 hot.
My car would run great until it warmed up...sound familiar? Quick and easy test you can do at home with a multimeter.

danziger

I concur...check the injectors. My Formula would start fine and idle nice, but then develop a "miss", which would gradually get worse until stall. Turns out two injectors were toast and a few more headed that way.

topfile

Mechanic reports that the compression tested fine for both #6 and #8.

Further he removed the Distributor and confirmed wiring and harness looked good.

Anything Else ? thanks for the suggestions.

topfile

He checked that the injectors were getting current. Next he'll pull them and have them tested. I'll advise you as to the results.

Thanks! I'm hoping it'll be that easy.

Pairof91rss

theres no need to pull the injectors to test the resistence...all you do is pull the harness to each injector (1 at a time) and check with an ohmmeter. One lead on each of the pins inside the injector...they should read about 16 ohms each...and all within about 1 ohm of eachother. Pulling the injectors would show which ones work...but I think one could diagnose that easier without the extra cost of having all pulled and flow tested. Might as well replace the injectors if youre going through all the trouble to pull them and have them tested. Youre already out plenum and throttle gaskets. My guess is a couple of them arent working at all, or at least nowhere as efficient as they should...
Get a set of Bosch III injectors (19# for 305, 22# for 350) instead of just replacing with the Multec's that came stock, you will be much happier!

Pairof91rss

Any new news?? Wondering what the final diagnosis was...

topfile

I'm to speak again with the Mechanic soon. However, last report was that the
highly suspects the ECM computer.

Thanks....more to come.

ASE doc

Hmmm, Calling a bad ECM is a common mistake when a tech cant find the real problem. As a drivability tech with GM I was told that "if you think its the ECM, keep looking" because while ECMs do fail, they dont fail often. The key issue I see here is that your mechanic has torn down the TPI system to "test" parts.

An essential step in diagnosis of any pattern failure is to recreate the failure. How can we bench test cold parts for a failure that only occurs when the engine is hot? Maybe your mechanic will get lucky and the ECM is the problem, though I doubt it. The ECM is much less affected by engine temp than injectors, pickup coil, ignition module, etc.

A good diagnosis must begin with a plan. First we develop a strategy, a list of suspects. Then we recreate the failure by operating the vehicle within the parameters where the failure occurs. Each time the failure does occur, we test a suspect part for any sign of failure, following our strategy. On very intermittent failures we may even connect our test equipment so that we can monitor parts while we operate the vehicle.

If we do not recreate the failure and follow a good strategy, we will never pinpoint the cause of a failure and diagnosis deteriorates into a series of expensive guesses as we literally throw parts at the car hoping each time that this part will solve the problem.

topfile

Ok here's the latest report from the Mechanic;

-While he had the distributor out he decided to replace the pick-up coil
to no effect. He noted that it was reading a bit low.

- Although he felt that the ECM was likely the problem he has since
decided that it's OK.

- Compression on both 6 and 8 cylinders tested fine.

-He didn't pull the #6 and # 8 injectors to test after all.

- While working with the distributor and verfing conections he noticed that
the fuel pump was no longer activating with the ignition. He now has the
tank out and is in the process of replacing the fuel pump.


Question....

1. Does it seem resonable that a fuel pump at 37 psi would cause a
poor spray with injectors 6 and 8?

2. What would account for the car stalling once warmed up?

Thanks to all who have contributed to this point. Please... feel free to comment on the above observations or answer one or both questions.

Pairof91rss

From the video I saw at FIC, the TPI system is non sequential, meaning that the injectors all fire at the same time. If #6&8 injectors arent working, its because the injectors are bad. Not sure about the pressure, sounds a little low, but not sure since its a 305, it may require less. Thought the 350 requires somewhere around 45.
Im pretty sure the pickup coil in the distributor is what should send the signal for the fuel pump to prime...so he may have done that himself when he changed yours out.
If it was me, I would be very suspicious...it sounds like either hes just shotgunning the situation and doesnt really have a clue, or hes running up your bill.
ASE doc is absolutely right about trying to recreate the problem before throwing parts at it. Im no certified mechanic, but I firmly believe that a simple injector swap to a set of Bosch III's would solve the problem. And finding out if the injectors were out of spec can be done in a parking lot/driveway with a cheap multimeter available at any auto parts store for around $30.
I wish you luck, and hope that Im wrong about your mechanic, and everything turns out ok...but you need to make sure that they are doing the right thing...THE CUSTOMER IS ALWAYS RIGHT!!! Dont let them make you pay for parts you didnt need!

southbay08

Don't let these guys rip you off!

ASE doc

Hey Topfile, Im sorry youre having such issues. As I meat to imply in my little lecture, Lol, any number of things can cause a pattern failure. A pattern failure is a failure that occurs under a certain repeatable set of circumstances. They are much easier to track down than intermittent failures that occur with no distinguishable pattern.

I took note that you say the fuel pump didnt run with the key on. The fuel pump relay should activate for about two seconds when the key is turned to "run". Be aware though that the ECM has a timer that tracks time since the last key cycle and may not activate the pump if the key has not been off for atleast 10 seconds. When the pump has run for two seconds with the key on, engine off, the ECM will then wait for pulses from the pick up coil/ICM, showing that the engine is cranking, to reactivate the pump.

Once the engine starts, the ECM again deactivates the fuel pump relay and the fuel pump is powered through the oil pressure switch/sender. Its important to verify that this system is operating properly. A problem in the oil pressure switch or circuit may cause the pump to either run on, even with the engine and key off, or to stop running even though oil pressure is sufficient to activate the switch.

I cant say that this is your issue but it is certainly worth looking at. In order to verify this, the car needs to be put back in running order and operated until the failure occurs, while watching fuel pressure and operation of the oil pressure switch. Hope this helps.

ASE doc

One more thing, Pairof91rss mentioned injectors. I wont say to go ahead and replace them without verifying that they are the problem, but they certainly qualify as a suspect. Does your mechanic have a labscope? If so, he can connect it to the injector drivers, one at a time, or using two channels, both at once. He can then monitor injector pulse while operating the car.

If the injectors are the culprit, he will see an obvious deterioration of the injector waveform. The injector circuits on the TPI are batch fire and use two drivers. Each driver runs one bank of 4 injectors and both banks fire simultaniously with each rotation of the crankshaft. The drivers in this system are the voltage controlled type. They activate the bank of injectors with one single pulse and maintain a closed circuit thoughout the injector pulsewidth.

This is also known as a "saturated switch" type of driver. Its given this name because the driver allows the injector coil to reach saturation much like an ignition coil. Just like an ignition coil the electro magnetic coil of the injector becomes saturated with current and develops an electro magnetic or inductive charge. When the circuit is opened at the end of the injector pulse, this inductive charge is released in the form of a voltage spike. A healthy injector circuit will reach 50 volts on this spike. A shorted injector circuit will pull down voltage and prevent the inductive charge from taking place, therefore reducing or eliminating this spike. A single shorted injector coil on either bank will have this dampening affect on the inductive "snap" as the driver opens the circuit. Go to the link below for an example an further explanation of injector waveforms. P.S. after opening the link, go to the bottom of the page and click on Injector Testing. Doc

www.autodiagnosticsandpublishing.com

danziger

I still think it is the injectors...

Pairof91rss

topfile

Ok Latest Report;


-Fuel Pump replaced and now it no longer stalls or cuts out.

- #6 and #8 cylinders still missing.

- #6 and #8 injectors had the noid light put on them and they are getting current.

So I'm thinking the injectors are bad too now. The Mechanic is torn between the injectors and the ECM.

1. Do you think the fuel pump went bad and debris from the failed pump could have clogged the injectors? Plausible?

2. Good replacement injector suggestions? Price?


All comments welcome. Thanks again to everyone. I'll report the outcome.


Side note: The Mechanic I known for years and we are we are both putting our heads together on this one. No worries about the price of repair as he has been more than fair in the past with me. He's the kind of guy that's helped me over the phone, on a saturday, while I'm trying to troubleshoot my daughter's car in the student's garage 200 miles away using his shop tools.

southbay08

If you are going to replace your injectors, the bosch lll's are the way to go.
Give us a call or pm us when you are ready and we will set you up with a set of 19lb bosch. Since we are one of the sponsors of this forum,, we offer a 10% discount to tgo members. If you purchase from our website just type in code TG11 at checkout.

ASE doc

ECM will not cause two injectors to malfunction. If you read my post on the injector circuit carefully, you will remeber that the injectors are split into two banks. The ECM has two drivers firing 4 injectors each. A bad driver in the ECM would cause an entire bank to misfire.

A failed pump may have put off debri. However, the filter should have caught that. Sediment and varnish deposits may have built up in the injectors or rail clogging injectors 6 & 8. Their position in the flow of fuel through the rails does make this explanation plausible. Be sure when you do replace the injectors to clean the rails as well as possible.

Keep in mind also that a noid light may not show a weak circuit. As long as the driver is functional, even if the circuit to one or more injectors has high resistance, the noid light will flash even though the injector powered by that circuit will not function properly. This is why a lab scope is the best way to test injectors. The lab scope's "picture" of the waveform will point out any type of weakness in the driver, circuit, or injector.

topfile

New Report

I agree that the ECM is likely OK. Also, the Mechanic thinks the injectors are unlikely
as we’ve now noticed that the missing only occurs after warming up. He’s concerned with the results of the compression testing. We‘re thinking a blown head gasket or warped head could be the problem. I’ll mention the insight into the fuel rail to him. He doesn’t have a lab scope.

He’s to check the timing chain soon, to see if it’s stretched. He’s also concerned about the lower intake as he understands Chevy had trouble with this. It was replaced about 4 years ago. Worn cam also crossed his mind.

Additional Symptoms:
-Compression Test of 8,6,4,2 Head
#8 100psi cranking/ 65psi running
#6 75 psi cranking/ 65psi running
#4 no data
#2 100psi cranking/ 65psi running
- Heater blows hot after warm up
-#6 and #8 miss starts only after warming up for 5 minutes or so.
- Can put car in gear while engine is cool and no miss occurs
- I noticed a hole in the line going to fuel vapor charcoal canister

On going Symptoms;
-Stalls after about 3 miles of driving (no longer per Mechanic)
-Must sit and cool for about an hour and then restarts(no longer per Mechanic)
-Missing on 6 and 8, pulling these plug wires and it runs the same
-Has spark on 6 and 8
-Plugs don't look fouled
-code 42 and 32 set
- Fuel Pump failed during troubleshooting
-Fuel pressure checked and good, (had been 37psi)

Actions taken;
- replaced ignition coil and module
- plug wiring order was verified
-Fuel pressure checked and OK'd
-Replaced Pick-UP coil
-replaced plugs

Any ideas? Anyone please comment!

ASE doc

Dont assume that because the problem occurs only with engine warm that its not injectors. In fact I would be looking very closely at injectors 6 & 8. Check their resistance. it should be 12-16 ohms. If 6 & 8 are low, they are probably bad. Test them again when they are hot, where the problem occurs. You almost have to have a lab scope for this.

Sonic testing them with a stethiscope may point out a failure if its severe enough. Try listening to the injectors as the engine warms up and listen for a change in their tone as the miss starts. Then, while theyre still hot, check resistance. See if its lower than when cold.

An injector that works fine when cold can go bad when hot. Much more common than a head or manifold gasket that leaks only when hot. Also, the compression numbers are all low. I assume he tested compression without holding the throttle open. Standard method is to hold throttle wide open when cranking for compression test. Otherwise compression reads low and results are hard to compare to known good values. Therefore they dont mean much. For the results to tell me anything, the test will have to be repeated with wide open throttle. Sorry

Pairof91rss

Just wanted to let you know that my car would only start acting funny AFTER the car was warmed up. I changed out my injectors and my problems went away. No longer stumbles and it now idles smoothly.
Its a pain in the a$$ to change the injectors, but well worth it. You can get a set from FIC or Southbay for less than 200. Listen to ASEdoc and test the resistance on your injectors...all of them hot and cold.
Im begging you, just do a resistance test on the injectors...ask your mechanic to do it and watch him do it so you know how yourself.

southbay08

If you choose to purchase from us, since we sponsor this forum we will give you a 10% discount. Use TG11 when you check out.

topfile

Was able to check resistance of 4 injectors. Since the my Mechanic was on his way out I was in a hurry. Didn't get to warm it up so all measurements are cold. Outside temp here in VA is about 92F and my meter lead resistance adds only about 0.2 ohms
to each reading.

So here it is including meter lead resistance as stated above;

#8 = 8.6 ohms
#6 = 10.0 ohms
#4 = 8.5 ohms
#2 = not measured

#1 = 13.1 ohms
#3 = not measured
#5 = not measured
#7 = not measured

So what do you think?

southbay08

Looks like you need a set of injectors. Numbers 8,6, and 4 are bad, and we don't even know the resistance of the others.

Pairof91rss

Hate to say I told you so, but...lol
Not really sure why the other injectors werent checked, as I didnt have any trouble getting to all my injectors on 91 350 TPI.
All I can say is that when a few members of the site offer ideas or advice...especially for free or very cheap ways to check, maybe next time look into it...its been my experience that 99% of the members on here have the best intentions. I think if you would have checked these sooner, you might have saved yourself some money on parts you didnt need, but its also possible that the parts you have changed out could've been bad now or in the near future. I do apologize if I sound condescending, as that is not my intention, and Im not disgruntled that MY advice wasnt your first choice...all Im saying is that quite a few people like ASE doc, who sounds very knowledgeable, suggested the same thing, checking the resistence on your injectors. Of course troubleshooting a problem without physically checking the car is not an exact science on forums, but I think you get what I mean. Im glad you may have finally tracked down your problem, and I would like to know the final outcome. Good luck

Pairof91rss

Just wondering though...looks like all injectors on one bank are shot...same way with mine before I changed them. Why would one side read so far off? has this happened the same way to anyone else, where one bank of injectors is out of spec???

topfile

Not really sure why the other injectors werent checked.....

Simply ran out of time. The Mechanic was literally walking out the door. I checked
them myself as he doesn't typically use an ohm meter. He prefers the test light probe as he finds it much faster for checking circuits.

when a few members of the site offer ideas or advice...especially for free or very cheap ways to check, maybe next time look into it...its been my experience that 99% of the members on here have the best intentions.

I appreciated your's and everyone's input. I've looked into all advice given and have always found it helpful and well intentioned. I truely hope no one here feels otherwise. For all who've taken their time to contribute their own experiences I offer a heartfelt and sincere thank you.


I'm in about $280 since I 've started.
For that my trusted Mechanic replaced.

Fuel Pump (defective and one heck of a difficult job by the way)
Ignition coil (not defective)
Ignition module (not defective)
Pick-UP coil (not defective)
Distributor Cap (not defective)
Plugs (not defective)
plug wiring order was verified
Fuel pressure checked
Checked Compression

So I now know the car better and got to converse with you fine gentlemen. Maybe,
just maybe others will found this thread helpful too.

Thanks again and specifally to the following for their superb input to this point;
ASE doc, Pairof91rss ,southbay08, Danziger, five7Kid, Douchermann.

Next will be the replacement of the Injectors.

I'll add more to this thread as time permits and results come in. As always please feel free to continue commenting. Thanks!

Pairof91rss

Honestly, I think $280 for the fuel pump install alone youre doing pretty good.
And thank you for a very polite and warm response...I was afraid that I came off like a jerk, Im still pretty sure I did. Hope youre daughters car runs like a top in the very near future!
Pairof91rss

topfile

Pairof91rss,

No problems.....again your comments are very much appreciated.

I'll repeat your last question in fact and hope someone can shed some light on it.......


Why would one side read so far off? has this happened the same way to anyone else, where one bank of injectors is out of spec???

broz70

I have been following your thread and have found it extremely helpful. My 89 IROC is acting similar. Runs fine until warm, then floods and stalls out. Not throwing any codes. Won't restart for a few hours. I've changed just about every stupid sensor in the engine. I did have the injectors tested and 2 replaced about 1 or 2 years ago. After reading the posts here I will have them all retested. Thanks.

danziger

Please post your results after replacing the injectors. My reasoning for them to get worse as they warm up is that the solenoids' windings are affected by the heat.

sack23

iTrader: (2)

I'm having the same problem here. Already checked the cylinders and I have spark and compression. I did noticed today that when I unpluged the last injector on the passenger side the car ran better. Im buying a voltmeter tomorrow and checking the injectors

thanks to everone helping here.

cliff1970

lots of good info here. hope i can get my car going now

sack23

iTrader: (2)

Ok checked the injectors today, sure enough the first injector on the passenger side had only 8 ohms,

Thanks to everybody here for the help.

broz70

Checked the cold resistance in my injectors. Four of them are reading less than 10 ohms. The lowest is 7.8 ohms. The two which were previously replaced are reading 16.4 ohms. I will post the result when I change them.

danziger

It seems that at least 50% of the time there is a "miss" or stalling/starting problem, the injectors are the culprit. Since you can get a nice set for under $300 if you shop around, I'd almost reccommend changing them as "maintenance"...

topfile

Just got my 8 rebuilt injectors delivered to the house today. All measure 14.5 to 14.8 ohms. Next I'll give them to the Mechanic to install.

Glad to hear this thread has been helpful. Thanks to all who have shared their knowledge.

Going to have the Mechanic replace the EGR while he has the intake off. My EGR
rest directly under the Plenum. He said he'd clean it all that while it's off. This should
address the code 32 I mentioned in the originating post.


I'll keep you all posted as to the outcome.

ninetyone

iTrader: (2)

You should be getting a reading like 0.013 for a good injector

ninetyone

iTrader: (2)

code 42 is a knock sensor

topfile

I think it must be a scale thing. I read mine on the lowest ohms scale
for the most accurate reading.

It's a 91' Z28 with the 305. Code 32 points to the EGR and Code 42 not sure.

Appreciate the comment. Thanks.

Another good thread with the same issues;

https://www.thirdgen.org/forums/tpi/...-when-hot.html

The Mechanic said he'll get to it very soon as he's now very curious.

ninetyone

iTrader: (2)

I told you that code 42 is your knock sensor.

broz70

Changed my injectors and while I was at it the MAT sensor which is under the plenum. It was a pain in the butt for sure. The lower runner bolts are tough to find and reach. There is a hidden bolt to each lower runner which threads from the back through the manifold into the runner. However, now my car runs fine. This thread was extremely helpful. Thanks to all those who posted. I guess what I learned was when I had the two injectors changed previously, I should have bucked up and changed them all. It would have saved me a lot of headaches. And while the plenum and runners are off its probably worth changing low buck items like the MAT, thermostat, etc.

night11wolf

mine was doing the same thing with the stalling i have a 350 tpi and the code 32 came up and i took the tpi and replaced the egr valve underneath and it runs great now it idles right and i have no other problems with my engine at all but its only been a week so i really dont know yet but it seems we had the same problem so just get that replaced and it should work