ZROC86

Ok the car has been running rich. I don't know why.

Last night was cruising to go see Starsky and Hutch about 1500 rpm and then it surged down to about 500 rpm then back up. It did that like 5 times. Then I was able to actually accelerate insteaed of "coast" and it didn't do it.

Also yesterday morning I shifted into reverse to back out of a parking spot and as I started to push the gas it stumbled and died. I started it back up and it did it again. Any one have any ideas what is going on?

jfreeman74

I would check the fuel pressure, and ignition system. Sound like an ignition problem to me. Is it giving you any codes when it dies. Mine was doing this and it turned out that my distibuter was installed about 45 degrees off when I put it back in after doing some engine work. I don't think that is your problem unless you have done anything to it lately. I would still check your timing and all your wires.

ZROC86

Just replaced cap and rotor. Got codes 34 and 36 I think. Disconnected the battery to reset and see what I get now. When I started it up before disconnecting it stumbled a little.

jfreeman74

Is the EST connector plugged in?

ZROC86

checked codes and only got code 36. What is the EST connector? Drove the car a little last night it stumbled some and gets really loud about 2500 rpm, but I think my CAT is rusting out. I doubt highly doubt this but could the CAT becausing this? I'm pretty sure no but thought I would ask the more knowledgable people.

jfreeman74

Sounds like the Electronic Spark Timing(EST) wire is disconnected somewhere. Look for a single brown wire under the cowl on the passenger side. Try doing a search for EST or Electronic Spark Timing.

MikeInAZ

The car is running rich because you are not running in the "normal" calibrated mode you are running in the limp home mode because you have a trouble code.

Code 36 is a MAF burn off relay for about 12 bucks. While your there and since they are the same age probably I would replace the MAF power relay and the fuel pump relay.

If this isn't the culprit you have not wasted your money as you have new relays (old ones get tired) and you can eliminate them from your diagnostic tree.

When your car enters limp home mode your fuel mixture is enriched, your car won't go closed loop and your TCC won't lock up.

In other words your MPG goes to squat and it runs like ..... well you know.

steven90GTA

my dad had a problem similar to this in his 93 350 throttle body truck he would be driving and it would drop idle and run like a diesel because some little chip in his distributor was failing

jfreeman74

Code 36 is also the code you get when you disconnect the EST wire. The MAF burnoff relay would be the next step though.

ZROC86

just replaced the burn off relay. the est wire looked like it was still connected. I disconnected the battery for a while but not sure if it was long enough though. I went by the number on the relay and it watched the same one as the power relay i think. is there a difference in the two?

MikeInAZ

The burn off and power relay are the same and are interchangeable. The fuel pump relay calls for a different number but is also actually able to be interchanged.

Sorry I am giving you this advice too late but maybe it will help someone else. If you have a bad burn off relay (code 36) you can swap it with the power relay.... clear the codes... and recheck.

If you then have a code 34 then that relay is bad. If you still have a 36 then it isn't the relay causing your problem.

Sorry for the late advice but your post about the same relays reminded me.

ZROC86

Checked the codes today and got 33 and 36. But I disconnected the MAF to check the hook up and forgot to reconect because I had to leave with a friend before I could finish everything. So I'll have to clear the codes to get rid of that one. But 36 came back again so... How do I check if the MAF itself is bad?

MikeInAZ

I may be wrong here but at least consider this. Any trouble codes regarding 33,34, 36 and 44 can be inner related and one can affect the other.

Generally when dealing with any of these codes you will want to check connections, the relays we spoke of and vacuum lines.

If you actually had a bad MAF I believe your code would be distinctly a 33.

On a 36 the general diagnostic is:

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.

And what triggered it:

MAP sensor signal voltage was too high (low vacuum) for 1 second when throttle opening was under 2%.

I will also tell you this. The 1986 PROM was defective. They upgraded it and the old one would send some false MAF signals.

You can read a bit about it here:

http://www.gmtips.com/3rd-degree/dox/tips/ecm/prom.htm

Thought of a couple of more. Obviously if you can beg or borrow a known good MAF to see if the code clears and I have heard of unplugging the MAF while running to listen for an obvious change. No change..... bad MAF.

ZROC86

cleared codes again since i messed with the maf. now i am getting 34 and 36.

MikeInAZ

Did you cut the screens out of the MAF ?

Or is it bone stock ?

ZROC86

It still has the screens and is bone stock as far as i know. it is a bosch maf.

elcamin0_77us

Here is some Code Discriptions
Bill


CODE 34 - MASS AIR FLOW (MAF) SENSOR CIRCUIT (GM/SEC LOW)

Circuit Description : The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The Electronic Control Module (ECM) uses this information to determine engine load for fuel delivery control.

The oil pressure switch or the ECM, through control of the fuel pump relay, will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor.

The ECM provides a current limiting 5 volts on the signal line (CKT 998). The MAF sensor then changes the signal by dropping the voltage so that with low air flow the ECM sees a low voltage and a high air flow will cause the ECM to see near the 5 volts supply.

Test Description : Numbers below refer to circled numbers on the diagnostic chart.

Code 34 indicates that the ECM has seen low air flow less than 2.5 gm/sec. (low voltage) for one second when:

Engine is first started
OR
RPM above 600
Throttle Position Sensor (TPS) above 6%. To obtain 6%, the engine has to be running at about 2300 rpm in neutral.
A Code 34 may be caused by an engine that exhibits a low, rough, unstable or incorrect idle problem. If this condition exists, disconnect the MAF sensor. If the unstable idle still exists, see Diagnosis By Symptoms - No Trouble Codes Stored. (Rough, unstable, incorrect idle, or stalling.) If the idle improved with the sensor disconnected, replace it. This test will determine if the conditions still exist to set a code or if the problem is intermittent.
With the MAF sensor disconnected, the ECM should see a high signal voltage and set a Code 33. If a Code 34 resets then the wiring or the ECM is at fault.

Diagnostic Aids : A low, rough or unstable idle could result in a Code 34. Also be sure air ducts are tight and not cracked. Check CKT 998 for short to ground. Refer to "Intermittents" in Diagnosis By Symptoms - No Trouble Codes Stored.

CODE 36 - MAF BURN-OFF CIRCUIT

Circuit Description : The Mass Air Flow (MAF) sensor measures the amount of air which passes through it. The Electronic Control Module (ECM) uses this information to determine engine load for fuel delivery control.

Due to contaminates in the atmosphere a residue may build up on the MAF sensor sensing wire. To maintain an accurate reading from the sensor, a "burn-off" cycle will occur when the ignition is turned off after the engine had been running a specified amount of time and engine warmed up. The burn-off function is enabled when the ECM grounds CKT 900 which energizes the MAF sensor burn-off relay. With the MAF sensor burn-off relay energized, voltage will be supplied to the MAF sensor terminal "D". Voltage will also be supplied through the normally closed set of contacts in the MAF power relay which will supply 12 volts to terminal "E" of the MAF sensor.

Test Description : Numbers below refer to circled numbers on the diagnostic chart.

This test will determine if the burn-off function is operative or if the Code was set due to an intermittent condition.
Checks for continuous 12 volts supply to burn-off relay.
Grounding CKT 900 should energize the relay and close the contacts. With the burn-off relay energized there should be 12 volts supplied to the MAF sensor on terminal "D & "E" (CKTs 993 and 994).
Diagnostic Aids :

The Code 36 could have been set due to a poor connection at any of the relays or the MAF sensor. Be sure that these connections and terminals are OK. A faulty MAF sensor should not be considered as the cause if Code 36 is set.

Refer to "Intermittents" in Diagnosis By Symptoms - No Trouble Codes Stored.

vance

What purpose would it serve to cut the screens out of the MAF?

ZROC86

I took a look at my ecm just to see where it is and there isa blue sticker on it saying it is remanufactured. i'll try to get pics up.