dans78ta

I have a 1991 Trans Am 5.7 L tuned port injection 78K miles 2nd owner clean collector quality.


Started acting up with gremlins and need some advice. At cold or hot start up it cranks and cranks and cranks super fast like a car would do with a timing issue. The only way to get it to start/run is while cranking push accelerator completely open/down. Then it starts but sputters while running, eventually coming out of a sputter idling smooth, but then back to sputter 3 mins later, then back idle smooth. The CEL(Check engine light) gives code 15 but this code is a temperature related code. It is very strange... When check engine light on it idles smooth, light goes out on its own and engine idles rough and almost dies.



I changed the TPS(Throttle position sensor) and symptoms went away for about 250 miles. Then same symptoms again. Now it Idles but won't accept any acceleration unless at a full throttle it tends to come out of it. I thought the sensor maybe went bad again and I put another new one on it. Nope, same thing.. Acts like it is starving for fuel, but then next minute its not. Now when I open the butterflies in the throttle body all the way open and crank it, it starts right up. While it is idling good, I accelerate it and it kills the motor.


I have created a check list and this is what I have done to is as I go through troubleshooting it. I'm still seeing same gremlins/issues.


Here is what I have done so far:
New Distributor Cap and Button
New Plug Wires
New MAP sensor
New Knock sensor
New Temp sensor
Throttle Position sensor/switch
Took Module in distributor to have tested(checked good)
Checked fuel regulator (checked good)
Checked Ohm reading on injectors(checked good)
Checked fuel psi at fuel rail (40psi)


Could it be EGR?
What about fuel pump? I can hear it bzzzzzzing in tank and fuel pressure at 40psi?

I feel as if I am chasing a rabbit hole sometimes.. I don't know what else to try. Should I change out the EGR valve? It sits directory underneath the TPI Plenum and hard to get to but if that could be it, I'll take the TPI apart and do it.

Thanks everyone! Let me know thoughts, advice, concerns?

Slowridr

iTrader: (1)

I have a 91 5.0 TPI 5 spd. Have some similar issues. I have real bad hesitation/bucking when cold. Car gets warm and it virtually disappears. Good luck, I've checked/changed many of the things you have. Took it to a mechanic had them check it out and said it was the injectors but I ohmed them myself at 17 they did at 14 and according to some gurus on 3rd gen that should be still good but stopped short of saying with 100% certainty. This is very frustrating. I guess next check for me is vacuum lines. This stuff can get expensive real fast if you are not a practicing mechanic, lol.

dans78ta

Thanks. I got the EGR off. When I pull the diaphragm all the way full travel and plug the inlet, it slowly opens up which seems like it should not do. Correct? Doesn't that mean it is leaking off?

Does anyone know if you can put a EGR plate over the intake and do away with it completely on a Tuned Port Injection motor? I understand with so many sensors in place on this model it may be necessary to have. Probably will just go buy another one, but just wanted to ask. Wow, these have gone up in price over the years.


Any ideas guys? What else could I try?

92purpz28

iTrader: (1)

I had similar issues and I replaced my coolant temp sensor. What was happening was the sensor was telling the ecu that it was -45 outside and the ecu told the injectors to dump wayyy too much fuel on startup. The only way I could get it to fire was to slam the pedal to the floor which tells the ecu to cut flow to the injectors. I would take an ohm reading of your CTS and see what it says

dans78ta

I'm just going to put a new EGR on it...


I put a new temp sensor on it and notice yesterday the connector and the wire back a few inches isn't in good quality. I could have a faulty wire leading back to the ECM. I clear the CEL but it still comes back after 3 mins with code 15 which is temp related... I might be onto something here!! I know I have to be extremely careful testing wires back to ECM as it can damage ECM. Any recommendations on how I could test the connection to the Temp Sensor?

92purpz28

iTrader: (1)

Just disconnect the harness with the key on and put a meter on it to verify its getting voltage. If its getting voltage then you need to ohm the pins on the sensor itself. Can't remember the exact reading but you can look on here and it will tell you

dans78ta

okay I tested voltage from ECM and I get 5 volts. The sensor itself shows 0 zero ohms. That can't be right...? I checked my meter and its fine. Its a new sensor.. maybe its a bad one?

92purpz28

iTrader: (1)

Possible you may have a bad sensor. The bad one I had wouldn't ohm out either so I ordered one off eBay. I think I paid like 8 bucks for it and got it within a few days. I checked it with my meter and got an ohm reading before installing it.

Bob88GTA

iTrader: (2)

If you're reading 0 ohms, its showing the sensor is 285 degrees. I had the same problem many years ago. Car thought it was overheating.

dans78ta

I did get 5 volts to the sensor. The sensor reads 0 ohms on a 50degree day. I think this new sensor is junk.. I took it back to O'reilly and took my meter with me this time and bench tested the one they exchanged for me right there before I left and it had proper Ohms. So you can figure I was excited to get home and put everything back together.

I went ahead and replaced all of old vacuum lines, EGR, and now put the temp sensor in. I notice there is also an intake Temp Sensor IATS. Maybe I should have just went ahead and replaced it too. Anyway.... I buttoned everything back up and cleared the CEL with my OBD scanner. I started the car, and it starts right up like never before!!! The Bad: It idles terrible(like a dead cylinder) and runs rough.. but it allows me to accelerate without nose diving and it starts perfectly now. Wow! I'm much closer to painting this bug in the corner!!

Any ideas now? I just put a new cap, button and wires on it. Perhaps I'll take the plugs out, maybe a fouled plug with all the problems of flooding and mixture issues? I'll start by pulling one wire off, and starting. If no difference then I'll pull the wire and plug from that cylinder and test it.

92purpz28

iTrader: (1)

I would verify spark on each cylinder and replace the plugs. Also be sure to check your oil dipstick. If it smells a bit like gas and is overfull I would change the oil and filter. If the injectors are dumping a lot of unburnt gas it can push past the pistons into the case and saturate the oil changing the viscosity. When I checked mine it was like water running out of the drain. Hey....at least its running!!!

dans78ta

After all new sensors and vacuum hoses, I put the car up on a lift. I got all the plugs out and number 2 cylinder(firing order #2) was completed saturated with fuel and completely fouled, not firing. I tested the plug wire and sure enough it was the wire. I replaced all plugs and new wires with OEM AC Delco. Buttoned it up and fired it up... fingers crossed...... It accelerates perfectly, and runs perfectly smooth down the road!!!!! I am a happy man now!!

The thing I notice now is that is idles at around 400-500 rpm which is way to slow. I come to a stop light and it almost feels like its going to die. In fact it did a couple times and I just have to keep my foot on the peddle to keep idle up. Surely this is simple set screw, but I don't see one.

How can I set the idle up? Or maybe I keep driving it and the ECM has to reprogram itself to find its proper idle point?

Slowridr

iTrader: (1)

I am glad to hear that! You should be all set for a while. You basically addressed all the major tune up items as you chased down the problem you were having. Time to enjoy that car!

I think you can adjust idle on these cars but it's set at the factory to not ever have to be changed. There is a knock out plug that you have to pull to give you access to the idle set screw. I think you also have to do something to the tps sensor too. Maybe someone will chime in on this.

92purpz28

iTrader: (1)

Before adjusting the idle grab your meter again and test your tps to see what you get. Google how to test your tps, its pretty straight forward all you need is a paperclip and a meter. Make sure you fully sweep it to WOT to see if it has any bad spots on the contacts. If it tests fine then I would bump up the screw on the throttle body. Its possible that someone adjusted it to compensate for a high idle due to vacuum leak

ploegi

It's also possible the IAC motor simply isn't doing it's job..... Might be time to give the TB a good cleaning, and see what things look like.

dans78ta

It has been a while since I gave an update to my post.. Unfortunately my 1991 5.7 TPI gave me trouble around 350 miles after I posted that it was fixed. I thought we had it fixed... It was running great.... THEN THE GREMLINS STARTED AGAIN!.. So frustrating....
I was at a total loss of ideas/fixes, and decided to put it in the garage and put the car cover on it. It is so frustrating when you have a beautiful car and cannot drive and enjoy it (I posted a picture of my TA below).

I am getting motivated to begin working on it again.

I will attempt to explain what it does now.

1. Starts up fine
2. Idle is fine
3. Let engine get up to a good warm operating temperature
4. Put into gear and drive away.
5. Acceleration is great. If you put your foot in it, it pulls very strong!! Chirps the tires in 2nd gear... It runs exactly like a 5.7 TPI should..
6. Drive it around maybe 10 miles or so, THEN IT BEGINS TO RUN ROUGH FOR 10 SECONDS, CEL COMES ON THEN CEL GOES OFF, THEN IT DIES.
7. Starts back up fine, no CEL on dash at all and drives fine.. THEN the same thing.. RUNS ROUGH FOR JUST A FEW SECONDS, CEL COMES ON THEN OFF, THEN IT DIES.
8. CEL - I put a jump wire between A & B to get codes today and light gives me 1 long 2 shorts, next sequence is 1 long 5 shorts, next is 1 long 4 shorts

Here is what I have done so far:

1. New Distributor Cap and Button
2. New Plug Wires and Spark Plugs
3. New MAP sensor
4. New Knock sensor
5. New Temp sensor
6. New Throttle Position sensor/switch
7. Took Module in distributor to have tested(checked good)
8. Checked fuel regulator (checked good)
9. Checked Ohm reading on injectors(checked good)
10. Checked fuel psi at fuel rail (40psi)
11. Replaced pick up coil, and entire distributor (This was done on 4/2/2019. I was told it might be pick up coil) STILL HAVING SAME PROBLEMS

Tuned Performance

iTrader: (92)

Have you gone through the diagnostic trouble tree for 14 & 15 ?
http://www.chevythunder.com/cts_diagnostics.htm
http://www.chevythunder.com/cts_diagnostic_pg2.htm
you could have a defective ecm

Drew

iTrader: (58)

After four years chasing an issue being identified by a trouble code, it is safe to say that now is the time, if you haven't already done so, to seek out and obtain the novel - 1991 "Pontiac The Firebird - In the Service of Manuel". It is the touching epic tale of a young Firebird and the trials and tribulations of being an OBD I vehicle. Along the way you'll learn all about every trouble code Manuel encountered, and how he adapted, and overcame every challenge to reach enlightenment. In some cases the book is even still in print, and available on interactive CD-ROM, but often barely used copies appear on Ebay, or maybe even sometimes the shelves of your local library. I highly recommend it if for no other reason the entertainment value.



The thing about trouble codes, especially with OBD I is that multiple conditions can throw a code, and you need to follow the logical process laid out in the book to eliminate possibilities and isolate the issue to a single possible cause. I'm not moving the stuff off the scanner and trying to manipulate a 3" thick book to get a good scan, so you'll have to settle for quick photos. If they are illegible, blurry, hard to make out, spend the money and buy a copy. If they show up too small on here, right click on the image and view image for fullsize.





Good luck!

GeneralDisorder

iTrader: (1)

It's really pretty simple - you either have a bad CTS (seems unlikely - the parts cannon probably ruled that out - but test it anyway - parts store garbage could be the entire problem), or you have an ECM or wiring issue. The circuit is very simple. Hook up a scan tool and check the reported temperature. If the ECM sees a significantly different temp than is actually occurring it will DRAMATICALLY affect the fuel mixture control - up to and including causing the engine to stall.

The code 15 that you have essentially ignored for 5 years is the source of your problem. Sensor, wiring, or ECM. Simple.

STOP loading the parts cannon and spend your money and time on proper diagnostic tools to identify the ACTUAL problem. Guessing will yield unpredictable results and may even create additional problems by replacing good factory parts with cheap import parts store garbage.

GD

blacksunshine'91

iTrader: (10)

Drew,

Back the firetruck up! Are you trying to tell me that a Repair Manual from the actual people that built our cars would actually tell us how to fix the very car they designed? Sorry, but I'm a little skeptical because your completely ignoring the most likely culprit:

dans78ta

Drew: Thank you for the screen shots! This is great to have. I am looking into investing in OBD1 PIN connector cord for around $59 and download tune software to my laptop so I can see everything the ECM is seeing. I will give an update after I take my next journey into the abyss.

dmccain

iTrader: (2)

I had bad intermittent problems with a TPI car and it wound up being the distributor. I had changed a pile of s%it to no avail.

dans78ta

dmccain: Yes we thought it might be worth changing it out so we did. The pick ups in the lower section of the distributor are rust dust and corrosion so we thought that may have been it. All new ACDelco distributor put in, and now getting code 14 & 15 CEL. Symptoms are noted above. Strange though because we've changes ever stinking sensor including CTS. We are now looking at wiring the troubleshooting based on the diagram Drew(above) posted. Also investing in a scanner.