Hi I have a 91 L98 Auto.

Was driving the car for about 10 minutes, when the service engine soon light came on, and power was lost, sort of like a limp home mode.
as i was pulling into my building, car went back to normal and light disappeared.

I checked the codes and H32, H34, H36, H38 in module 1.0, and then H43 in the next module.

Anyone have any idea why this could be happening?

another issue ive been having is the car idles poorly when hot, it seems like it wants to stall even though its an auto.


Thanks in advance

 

I just checked all the codes in my book and all 4 codes that you have say bad ECM as one of the problems that it could be.Or possible bad ECM wiring.It also mentions MAF and sensors.This will give you a place to start. Look at chart below..

32 The most common cause of this code is a bad or intermittent EGR switch which is located on the EGR pipe between the exhaust manifold and the intake manifold. Replace this switch first when you get this code. Next, check electrical connections at EGR valve solenoid and then the ECM. Check all vacuum lines for leaks especially around the EGR valve. Possible ECM failure.
33 (1985-1990) Inspect intake system for leaks, Inspect for vacuum leaks, Check MAF connector and wiring, Check MAF for open using digital Ohm meter. Possible ECM failure.
33 (1984) Check vacuum hoses. Check wiring to sensor. Change sensor. Check connections at ECM.
34 Clean the throttle body. Check MAF connections. Replace MAF relay. Replace MAF Sensor. Possible ECM failure.
34 (1984) Check Vacuum hoses associated with MAP sensor. Check wiring and connections, particularly at ECM. Replace the sensor. Possible ECM failure.
35 Check fuel pressure, injectors, leaking throttle body. Change the IAC valve.
36 Check connections at MAF, MAF relay and MAF Burn off relay. Check resistance of MAF relay and MAF burnoff relay with digital Ohm meter. replace if less than 18 Ohms. Possible ECM failure.
41 Check wiring at ECM. Possible PROM failure, or incorrectly seated PROM. Reseat PROM. Possible ECM failure.
42 Check wiring at ignition module. Replace ignition module. Possible ECM failure.
43 Check ECM wiring. Replace knock sensor

 

91 L98. Check the injectors.

 

You '91 has a Speed Density (SD) input so I'd start by checking the wiring to the Manifold Air Pressure (MAP) sensor and maybe replace said sensor.

The MAP sensor is located to the Right side and on the rear of the plenum.

 

Thanks for the responses,

the injectors are brand new, and they are from FIC on these forums.

Not sure why all 5 things would fail at once, maybe its the ECM thats bad? is there a test i can do?

I took the car for a drive the other night and the service engine soon light would come on every 10 to 15 minutes for about 2 or 5 minutes then disappear.

strange..

 

The easy test would be to swap the ecm with a friends 91 ecm. I have experienced multiple codes thrown at once on my 86 and it was the ecm. Fortunately it was $200.00, cheaper than my mass air flow sensor. Maybe you can locate a Forum member with a 91 willing to help out.

 

Yea that sounds like a good idea, however im in Hong Kong and that will be kind of hard.

How likely is the ecm to fail? Is there a test I can do to see if its actually the ecm?

Took the car for another drive today and no lights no codes, nothing... so wierd.

on the other hand the problem when coming to a stop and the engine wanting to stall when its really hot is still there... any idea on that one?

thanks for ur help so far!

 

When you say "really hot", how hot are you talking about? Is it at normal operating temp., or is it abnormally high?

 

sorry, i mean when the temp is above 100c up until 116c

 

On my '88, It once had a prob with the ecm that was causing the
ignition to advance abnormally. Try checking your timing and see if it's too advanced. By the temp you stated, it doesn't sound like it's too bad, but it's a place to look. Also, check it at different engine speeds to monitor how it behaves. I'ts hard to simulate driving conditions, but it might give some hint as to whether things are timed correctly.

 

My '95 does gives those codes when I start it with or have a low battery charge.

 

Are these codes or lotto numbers

 

My 91 had the exact same problem. The engine ran fine but, I would get an intermittent SES light. After everything checked out fine (no vacuum leaks, EGR Solenoid good), I changed the EGR valve and the SES light never appeared again.

The EGR valve also, cools the combustion chamber by injecting exhaust gases back into the combustion chamber which could be the reason why your engine gets hot in traffic and wants to stall.

 

I have a feeling this is going to drive me crazy looking for the culprit...

I was using accel injectors before at 24lbs, which dumped too much fuel, so i bought the new injectors from FIC on these forums, then i decided to replace the EGR Valve, along with the IAC and cleaned the throttle body, new spark plugs too...

maybe the knock sensor wiring is loose or something, ill have a look and see.

whats the best way to check for a vacuum leak?

 

Ok so i reset all the codes and this time, only H43 came back..
im guessing the knock sensor, which makes sense and the coolant was just flushed from there...

are there any typical problems that can come from removing and replacing the knock sensor?

 

Not really as long as you did not use any sealant on reinstall that will cause problems. It must be clean. I have read in the past the engine does a KS test on start up by changing the timing in the ECM if it does not get a knock it will set a code. Check the plug clean it with contact cleaner I have read some plugs break easily.