I have a 1987 IROC 305 TPI with dual fans. The problem I'm having is that the fans have started turning on when I turn the key on. at the same time the engine started to have a hard time starting. It will chug-a-lug and sometimes backfire for about two minutes. I turn the key off and re-start and it seems to run fine. GM dealer replaced the ecm and it seemed like the problem stopped for a couple of weeks but now it's started acting up again.

Do the fans turning on prematurely have anything to do with the hard start problem?

Also the car will run fine for about 30 minutes and then it will stumble, lose power, the check engine light comes on and then it stalls when I put in the clutch. When I let the clutch back out while I'm rolling along it fires back up and the problem is gone for awhile.

 

Sounds like a grounding issue in the harness.

 

Ok. Now the SES light turns on right? Then get the troublecode that was just stored. First rule of thumb, Retrieve any TC's, try to find the solution. If no solution is found, then get on this board and note the stored troublecode. I will help you but you gotta give me a starting point to be able to find a solution for you. I got a Blackberry cell eith automatic notifications. So when you post, I get an alert. I will try to help you out if the situation permits bro.

 

Here's the strange part, since the ecm was replaced the only code I get is 12 even though the SES light comes on when the engine stumbles and then stalls. before I changed the ecm I used to get TC43, TC33.

The GM dealer that I took the car to says the problem was either the ecm or the aftermarket prom chip (hypertech). Well I replaced the ecm like I sais and the problem seemed to go away for a while. Now it seems that once the engine warms up to full operating temperature, that's when things start happening (maybe 20 to 30 minutes of driving on the freeway). I just adjusted the IAC and checked the TPS (set at .57v), disconnected the battery cable and reset the ecm. The car starts right up an is running fine once again. It seems like one time a while ago when I plugged in the tester to check TC that's when the fan problem began. The fan turned on like it was supposed to but after the tester was removed it continued to turn on every time I turned the key on.
The Gm dealer told me to order a new chip which I've done and should have by the end of next week, but the chip manufacturer (Jet Performance) told me that the chip has nothing to do with how the fan cycles.

I know very little about the TPI injection systems, I'm an old guy who grew up in the 60's with the carbureted cars. This computer controlled engine is driving me crazy.

 

As the engine stalls, the SES light will always turn on. Call Jet Performance and tell them they are so Full of it. Befpre someone programms a blank EPROM, he has the ability to change when the EPROM turns on the fan. Example. A OEM MemCal has athe set temperature for the main fan to turn on at around 220*. With TunerPro, you can enter the bin file of a PROM and open up the bin. Within the bin file, you can change the main fan turn on temp down to 160* if you wanted to. So a chip has everything to do with how the main fan cycles. Here is proof....
Here is a bin file extraction of a 87 350 MemCal.. the one in red is where you can change the turn on settings in the chip...

Fan on at 107.75 Celsius = 225.95 Fahrenheit
Fan off at 104.75 Celsius = 220.55 Fahrenheit

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TunerPro Bin Data Export
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Source File: ABWN.BIN
Source Definition: $32B.xdf
------------------------------
Constants
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Fuel Cut Off, (Speed) 255.00 MPH
Fuel Resume (Speed) 254.00 MPH
Fuel Cut Off, (Engine Speed) 10031.02 RPM
Fuel Resume (Engine Speed) 9544.08 RPM
Fan Off Coolant Temp Threshold (A/C On) 104.75 Deg C
Fan On Coolant Temp Threshold (A/C On) 107.75 Deg C
Fan Off Coolant Temp Threshold (A/C Off) 104.75 Deg C
Fan On Coolant Temp Threshold (A/C Off) 107.75 Deg C
Injector Flow Rate, (Single Fire) 23.04 #/HR
Injector Flow Rate, (Double Fire) 23.04 #/HR
EGR Off (TPS) 7.42 % TPS
EGR On (TPS) 7.81 % TPS
TCC Unlock Speed (Low Gears) 26.00 MPH
TCC Lock Speed (Low Gears) 27.00 MPH
TCC Unlock,Speed (Higher Gears) 26.00 MPH
TCC Lock Speed (Higher Gears) 28.00 MPH
Maximum Spark Retard (Not In WOT) 20.04 Deg
Hot Engine O2 Timer 30.00 Sec's
Warm Engine O2 Timer 160.00 Sec's
Cold Engine O2 TIimer 300.00 Sec's
PROM ID 8161.00
Idle Speed Adder in Park/Neutral 50.00 RPM
Idle Speed Adder for A/C On 50.00 RPM
Max Accel. Enrich. Async Pulse Width 5.55 msec
Minimum Delta TPS For Accel. Enrich. 3.91 % TPS
Minimum Delta LV8 For Accel. Enrich. 20.00 Counts
Maximum BLM Value 160.00
Minimum BLM Value 108.00
MAF High Diagnostic (Error 33) Threshold 45.00 gm/sec
TCC Unlock Prevent/Auto O/D Engage Speed 75.00 MPH
Shifter Kickdown Prevent RPM Threshold 6375.00 RPM
TPS Kickdown/TCC Unlock Prevent -1st Gr. 3200.00 RPM
TPS Kickdown/TCC Unlock Prevent-Not 1st 3200.00 RPM
Max Spark Advance 41.84 Deg.
Initial Spark Advance 5.98 Deg.
Number of Cylinders 0.00
Min. Coolant Temp for BLM Update 50.00 Deg. C
Max. Coolant Temp for BLM Update 140.00 Deg. C
Min. MAT to Enable EGR -17.50 Deg. C
TCC Enable Coolant Temp. Threshold 50.00 Deg. C
Highway Mode Spark Enable Coolant Temp. 59.75 Deg. C
Highway Mode Spark Max Load Threshold 100.00 LV8
Highway Mode Spark Enable RPM Treshold 6350.00 RPM
Highway Mode Spark Enable Delay Time 10.00 sec
IAC Startup Park Position 144.00 Steps
IAC Control Deadband RPM Error (in P/N) 75.00 RPM
IAC Control Deadband RPM Error (Drive) 25.00 RPM
Min. Load Limit for TCC Lock, Low Speed 3.13 %TPS
Min. Load Limit for TCC Lock, High Speed 3.13 %TPS
TCC Min Load Limit Hysteresis 1.17 %TPS
TCC Min Load Limit High/Low Speed Thresh 32.00 MPH
IAC Startup Delay Time 1000.00 msec

 

Thank you for all the information. You really went out of your way to provide an answer. You clearly shows that the chip does have an effect on the fan control. I'm very thankful that you showed me this because I was going to cancel the order for the chip today. I didn't want to spend $172.00 for the stage 1 chip if it didn't have anything to do with the problem I was having.
I should have the new chip in my car by Oct. 28th. I'll let you know how it goes.

Last night I took the car out for a drive. It ran really good as usual for about 15 minutes than the engine stumbled, lost power and the SES turned on. I put in the clutch while we were rolling down the street and the motor stalled out as usual. I let the clutch back out the engine fired up, the light turned off and it ran fine for the remainder of the time I was out which was about 40 more minutes.

It's very strange. Thanks again for all of your help.

 

Any time.

 

Anytime bro.

 

Well first thing I would do is test the ECMs ability to store trouble codes. To do this just do something like disconnect the TPS sensor. That should throw a code and it should be stored. If its not being stored then we have to look into why not so we can actually see the real codes. I would also check the resistance of all your relays and solenoids. Its possible that you have a bad one with low resistance that killed your ECM then ran better for a while with a new ECM before killing that one too. The fans are kind of interesting but before I get into that 1. did they once work correctly? 2. Were they swapped in or has the wiring been modified? One should be controlled but the ECM and if the temp sensor was dead it would tell the fan to go on immediately to protect the motor but the other fan is controlled by a temp/ac switch so it should not be effected. The fact that both fans work together despite being controlled by totally separate means seems odd to me unless of course its been modified which many of our fan systems have been.

 

Sunday I took the car for a long drive that included both freeway and country roads. The car ran very smooth for about 25 miles then the engine stumbled and lost power. I put in the clutch while I was still moving and the engine completely shut off. When I released the clutch it fired back up and once again ran smooth for another 10 miles before it happened again. When I got to my destination I disconnected the power source to the ecm. When I was ready to leave and head back home I connected the ecm power source started the engine and it ran fine all the way (about a 1 hr trip)

The fan wiring is stock as far as I can tell. I did replace the fan relay and also the coolant temp sensor on the front of the engine. It seems like the problem developes when the engine gets warmed up.

I should have my new prom chip this week so I plan on installing it and see if it solve the problem. I'll also disconnect the TPS like you suggest to see if that sets a code.

It seems like the ecm might still be working because when I check for codes it flashes 12 repeatedly plus the engine starts up easily and will run smooth for awhile before it starts acting up.

The previous owner installed a Hypertech chip in 1996. I'm replacing it with a Jet Performance chip.

 

do you still have the stock prom?
put it in and see if the problems go away, then you'll know for sure it's the chip or not.
I tried a corvette chip in in my z28 once, the fan ran constantly just for an example

 

Update: I replaced the prom chip, the ecm and the problem still persisted. I took out my sledge hammer and was about to use it on the car. I thought it over though and decided to take another look to see what might be causing the problem. I traced the fan circuit in my service manual and discovered that the motor had a radiator fan switch on the passenger side of the block. I removed the connector and the fans didn't turn on. I replaced the switch and now the fans operate correctly. The problem with the stumble and stalling still continued. Someone mentioned that they had a similar problem when the fuel pump was going bad on their car. I put a pressure gauge on the fuel rail and saw that there was only about 20 lbs pressure. I changed the old fuel filter but the pressure didn't increase. I ended up taking the car to a mechanic who knows quite a bit about TPI motors. After doing some testing he came to the conclussion that the fuel pump and or pick-up filter screen was the problem and that it needed to be replaced. Not the easiest part to get to.

This is being done tomorrow so I'll let you know if the problem is solved. Thanks again everyone for helping me work through this problem.

 

Ahhh man. You could of done the fuel pump yourself, if you got a 5 ton floor jack and big jack stands. its a P.I.T.A. but I changed out my F.P. by myself last year. It was heavy (even with the tank being empty) but I had to drop it 3 times within 2 months. I eventually knew what steps like the hairs on the back of my hand. That sux bro. It could be a number of things. Does your speedometer work? I ask because I had a stalling issue last year, similiar to your case. The problem was a bad Vehicle Speed Sensor. But my speedo didnt work. So I went to Autozone and bought a speedometer cable. Once I got that bad boy in there, I never had a stall or a troublecode of a bad Vehicle Speed Sensor ever agian.

 

Also what you could do is when your IROC stalls, whip out a voltimeter and check the resistance on the Fuel Injectors. They probably are going bad when they get hot enough. Just a thought. The resistance should be at around 16 ohms.

 

I'm going to take a look at the injectors next, because after the pump was put in the motor has a hard time shutting off. It just wants to keep on running when I turn off the key. I think the injectors may be leaking now that they have the correct fuel pressure on them.