3D-Aircrew

1986 vert. Yesterday on the way home the car started to stumble a couple times. This morning in the driveway it started fine for about 30 sec and then stumbled and stalled. Would not restart … cranks but no go . Immediately checked the codes with a 33 and 36.

Time to dig in to the FSM

PS: Let it sit 15 minutes and tried to start it again and it started right up but NO CODES this time and no SES????

KyleF

While it is running, Tap the MAF lightly... don't pound on it, but let it know you are there. If the car stumbles, your MAF is going bad.

Having them both at the same time is interesting.
Code 36 is the MAF Burn off Cycle. This flags when the computer doesn't get the return voltage from the burn off voltage being sent to the MAF. So, either the MAF is faulty, the relay is faulty, or the is a broken wire.

Code 33 happens when the following 3 conditions are true at the same time:
1) engine under 2000 RPM,
2) MAF reading over 45 gms/sec, and
3) less than 25% throttle.

So, either your MAF is bad, TPS is bad, or a power relay is bad.

Do the tap test, test your TPS Voltage (.5-.6V at Idle, <4.5V at WOT) and then check your relays. If all checks out then dig in to the wiring.

3D-Aircrew

When I got home from work I started it and it started fine ... did the tap test on the MAF and nothing happened. Let it run for a few minutes until it started to act up and then stalled. Checked codes again … 33, 36 again. I had a new spare MAF in the box so I swapped it in and tried to start it and it wouldn't so I don't think it's the MAF.

Funny thing was that when I took off the MAF a thick fuel vapor came out of the throttle body if that's any clue.

I guess I'll check the TPS and relays.

KyleF

1) engine under 2000 RPM,
2) MAF reading over 45 gms/sec, and
3) less than 25% throttle.

If your MAF reading is high in Open loop, the car would be adding fuel to compensate. Idle should produce the other 2 conditions. May not be the MAF. If the voltage getting to the unit is low or high... it could affect the output as well.
The relays are like $15 a piece. You can check them, or just swap them.

Was the MAF you installed a hot film or wire style?

The car should start with or without a MAF. Not saying it is going to run well, but it should start/run.

JackDidley

Every time I had MAF codes, I changed the relays and fixed it. Cheap and easy fix. I will say the car never ran bad, just turned on the service engine light. Three times, I think in 170k miles.

3D-Aircrew

The original is the wire type MAF and the replacement was a hot film style.

I got the MAF power relay today at lunch and I'll install and test this evening. I don't understand why I'm going through these relays.

KyleF

Yea, it's almost so cheap to replace the relays it's not worth probing and checking, but throwing parts at a problem often gets us in trouble.

I had to hunt down an original style MAF to get rid of my Code 36 in my L98. The hot film style just didn't return the right voltage to the computer when it was monitoring the burnoff cycle.

How many times have you replaced the relays? If they both went down and have multiple times, you might have a grounding issue or wiring issues.

3D-Aircrew

Well I had a chance to check some basic things. When it was in a no-start condition I put a timing light on no 1 wire and I got a flash so I have enough spark to signal the timing light. I also checked the fuel pressure 45 with the key on and 40 while cranking and the pressure held for 20 minutes.

I got a new MAF power relay and it didn't help the no-start condition so I think the relay is OK … so now I have a spare. Running out of ideas. Back to the FSM Cranks but won't start section.

KyleF

Code 33/36 Should not cause a no start issue. Both of these are MAF related.

Did you put the old MAF back on and try to start it?

Here is a thought.. the Ignition Control Module can often be affected by heat when it starts to go. This can also cause a no start condition if it goes out. Not sure how it would drive a code 33 or 36.

My L98 had a 33 or 34 when I had a fuel rail leak and became very hard to start, if at all... until I smelled the gas and located the leak. You may have the opposite and have a air leak and too lean to start. Does it fire any cylinders while cranking or just nothing?

tequilaboy

Both failures point to a MAF voltage issue...likely high voltage in both cases...

The car is probably flooded due to the high MAF signal at start-up. Hold the throttle wide open to start, if it won't fire with closed throttle to clear the flooded cylinders.

Then go about diagnosing the high MAF signal. Possible causes: open circuit on MAF signal wire (signal is pulled up to 5 volts by ecm), bad power relay, bad MAF...log the unlimited airflow signal during cranking and after shutdown if you can.

3D-Aircrew

Yeah I put the original wire MAF back on and it behaves the same. It cranks sputters and tries to start and sometimes runs for a couple seconds then dies. Code 33,36. I was thinking about the ICM too but I was getting spark. This is an intermittent problem because sometimes it will start with no SES and run for a minute before sputtering out and dying.

3D-Aircrew

I tried to clear it by using full throttle and it behaves the same but only sputtering.

tequilaboy

Do you hear the fuel pump running during the 2 second prime cycle just after ign on? Maybe a bad fuel pump relay. MAF (power relay) gets its power through the fuel pump relay or oil pressure switch.

3D-Aircrew

I can't hear the fuel pump but I see it jump right up to 45psi immediately after I turn the key on. It turns out that my ICM was bad or intermittent. I put a new one in and have had the car running for 1/2 hr no stumbles no codes.. Now if anyone can explain how a bad ICM can trigger those codes, I'll be grateful. Thanks everyone!

KyleF

Not sure, but glad you figures it out. Usually ICM issues are a Code 42.

DUB

Glad to read you got it working.

DUB

catso

I would think that the codes seem to be a by-product of the misfires or slightly out of sequence spark. The more sophisticated OBD2 system would be able detect it, but of course OBD1 cannot.