KyleF

So, I got the car with a Code 34 but everything seemed to run OK. Drove it 1.5hrs home and around the neighborhood, etc. The code was a fairly new issue and the guy I bought it off of had put a new MAF and Burnoff relays in the car.

So, I ran the normal diagnosis. Checked TPS Voltage, ran the car with and without the MAF, cleared codes, checked... and so on. Here is what happened:

-Check Code - 34
-Check MAF - it is clean and brand new.
-Swapped Relays - Same condition
-Checked TPS Voltage - looks normal except it doesn't go over 4V at WOT, but very close (3.9XV)
-Ordered Remaned ECM
-Installed ECM
-Start up, Idle is rough but that is nothing new to other TPIs I have had after clearing the computer
-Smooths out after 2-3 minutes.
-Cool... on to next steps of checking general health of the car
-Check Timing (Unplugged EST) Timing was a couple of degrees off and I adjusted it back to 6*. When going back to turn off the car SES light is on.
-Pull Codes, Code 36 ( I think, Disconnecting signal to distributor could have caused it)
-Clear Code
-Start up, Idle is rough but that is nothing new to other TPIs I have had after clearing the computer.
-Take it for a drive ~15 min after it smooths out. No Codes
-Put back in garage
-This morning going to take it to work... start and SES light is on. Turn it off, check codes - Code 36
Go to turn it back on, no start.



Thoughts on next step?

Yes I plan on getting an older lap top, cable, and WinALDL soon, but really thought I could get this taken care of and set idle/timing without it.

The car has new MAF, New MAF burn off relay, new ECM, no damage apparent to any wiring, harnesses, or anything in the car. Now, it has a spectra MAF and it has the flat wafer style electronics rather than the Ring around wire and heat sinks of the OEM style.

RBob

iTrader: (1)

Unplugging the EST/BYPASS connector and running the engine should have set code 42. If not then either you didn't unplug the correct connector or the the ICM is possibly bad.

RBob.

wayshegoes

I had the same problem, I gave up and took to shop that knows TPI, they replaced the MAF and MAF relay, problem solved

What part number do you have for your relay, my understanding, from a lot of reading, is that people purchase the wrong relay, and or the repalcement MAF is just a POS, I tried a few different MAF sensors form rock auto before I took to shop

i will check the part number on my relay, and what brand maf

KyleF

Tan Wire/Black strip by the AC Box on firewall, passenger side.

KyleF

They are still new enough to read the part numbers, but the car is at home. Another member posted the original part numbers and I planned on doing some cross referencing this evening to double check.

I suspect the MAF may be a POS, but it didn't run or Idle better unplugged.

RBob

iTrader: (1)

Sounds correct, but did the ECM set code 42? If it didn't then there is another problem.

With the engine running and unplugging the EST/BYPASS connector, the SES/CEL should light up and code 42 should be set.

RBob.

KyleF

Actually, not sure. Wasn't inside the car while unplugged. Would it clear without disconnecting the battery?

Trying to get my feet set in all this again.

RBob

iTrader: (1)

Stored codes clear after 50 startups with no other codes detected. So in your case, it won't clear unless the battery is disconnected.

RBob.

KyleF

May have to revisit unplugging the EST. See wjat happens. If there was no code 42, what does that mean?

RBob

iTrader: (1)

It likely means that the ICM is bad and the base timing is not set correctly. It is also possible that it is an ECM problem.

Here is how it works: at key-on, engine cranking, the ECM electronically opens the EST/BYPASS line. This tells the ICM to clamp the EST signal from the ECM to ground. The ECM tests for this and sets code 42 if the EST line isn't clamped.

The open EST/BYPASS signal also tells the ICM to fire the spark plugs at the base setting.

Once the engine is running (goes over 400 RPM), the ECM electronically closes the EST/BYPASS signal. This tells the ICM to un-clamp and use the EST signal from the ECM to fire the plugs. This puts the spark timing under control of the ECM.

Now, when physically opening the EST/BYPASS connector, that is the same as when cranking. The ICM fires the plugs at the base timing, and allows the use of a timing light to set/check the base timing.

But since this also causes the ICM to clamp the EST signal with a running engine. The ECM sees this and sets code 42. As the ECM hasn't electronically opened the EST/BYPASS, it is an error condition.

In this case if the ECM isn't setting code 42, then the ICM isn't clamping the EST signal. Or the ECM is bad.

Note that the EST signal is how the ECM tells the ICM to dwell the coil (charge it), and when to fire a spark plug.

Of course all of the above is for a stock calibration. If the PROM/chip has been swapped or muddled with, all bets are off.

RBob.

KyleF

Nice write up. I am familiar with the function of the ignition system, but very useful information on how it determines to set the code.

The car had a re-manufactured ECM in it, I have now put another one in it. I know one from the parts store doesn't guarantee anything, but it's usually a low probability both are bad and exhibiting the same bad behavior. The chip is stock surprisingly considering it has a Vortech, Long Tubes, 3.70 gear, etc. Previous owner states it has not been changed and looked factory when I switched it over. I will have to go back through the procedure again to confirm. I haven't turned my old unit in yet for the core and won't until the problem is resolved.

My previous experience with ICMs going bad is usually heat related: I.E. the engine usually has issues once it gets warmed up. This car certainly exhibits none of that behavior or any issues once it gets going.

Sometime this weekend I am going to pull the EST and pay attention to the codes. The other morning it didn't start right up, but didn't have time to screw with it. So, I have to get back in there and see where I am at. Thanks for the insight.

KyleF

Just curious, seen mention of leaking fuel injectors in another thread... would a fuel pump that is on its way out have any influence on this?

I posed the question there as to why a leaking fuel injector would be a cause, seems being rich/lean would cause 02 sensor issue.

The fun of diagnosing a fuel pump issue on a supercharged car... there is a helper pump.

Going to get back into it this week.

KyleF

Found a fuel leak... and other issues.

For anyone who may look this up later or curious I started a thread about the car once I brought it home. Originally thought the Code34 and some tuning was all that was going to be needed... it is becoming much more.

https://www.thirdgen.org/forums/tpi/...-underway.html