Intermittant issue. Possible bad ECM.

[Vincent Vega]

My 88 has been having drivability issues that make it hard to rely on. When running right it idles smooth, has good power and seems quite normal. When it is "acting up", it idles rough, it miss fires horribly and makes it very unreliable. It will throw a code 42 from time to time, but it will clear it on it's own. I have checked and cleaned the connection from ECM to IGN module.

I ran the trouble shooting for a code 42 without being able to duplicate the problem.

When I run diagnostics all the ECM data values seem to be within specs.

The only two that are odd are EST and OPA3. EST never moves off 0. OPA3 varies.

The ECM outputs on the other hand are very odd. The first is 0000(normal).

There is nothing output for the rest. Nothing but the dashed lines you see when a value is unavailable for that component.

This leads me to believe I have a failing or failed ECM. Any thoughts from you ECM Experts out there? Any tests I can run to prove it is indeed bad?

[DAVES89]

I would think a new coil pack might be the first thing I try. Do you have an extra one?

[Ronnie]

I'm not familiar with OPA3. What is that?

[Vincent Vega]

Coil pack seems OK. OPA3 (OLDPA3)is something like knock sensor activity. The range is 0-255. Mine will show higher than that. Any thoughts on the odd ECM output values?

[D-a-n-i-e-l]

Have not had a knock sensor go bad yet but on my blazer I had a bad connector that would fall off the sensor and act just as you are describing.. could not hurt to disconnect it and see if the issues return.

[handmedownreatta]

Tap on the ecm when the car is running. If the solder joints are bad it will cause the engine to miss.worked for me.

[padgett]

Oldpa3 should not be zero with the engine running, I will always get some when the engine fires. Should not be incrimenting while driving except maybe coming off a stop.

[Vincent Vega]

OLDPA3 was in the 700's.. According to the fsm that is OK. Did the test from the fsm and it went up. Tried tapping on the ECM while it was running smooth. No chg. Also, the Crank sensor and cam sensor are new. Frustrating.

I'm not sure how the ECM outputs is supposed to be interpreted. Car running or not? When running I don't see the hi/lo values. When not running (ign on) It cycles back and forth from off to on. I can here the relays clicking. That doesn't seem right to me.

Edited August 6, 2013 by Vincent Vega (see edit history)

[Guest Mc_Reatta]

Go here and look at ECM Outputs vs Overrides on page 7.

Explains which can be done with engine on, and which ones need it off.

Reatta On-board Diagnostics Booklet - Reatta Owners Journal

[Vincent Vega]

Go here and look at ECM Outputs vs Overrides on page 7.

Explains which can be done with engine on, and which ones need it off.

Reatta On-board Diagnostics Booklet - Reatta Owners Journal

Yep. I have that book and the FSM. According to this My car says ECM outputs E001, and E004-E011 are not available with the engine running. All I get is the "= = = = =" message.

"If "= = = = =" Message Appears You Are Trying To Test A Device That Is Not Allowed With Engine Running: Turn Engine Off And Try Again."

- Why would those devices be unavailable to test with the engine running? It allows me to override them.

- With the engine off why do they automatically cycle from on to off?

- All devices appear to be working as I can hear the relays clicking on and off.

These are the oddities that make me suspect the ECM.

Can someone confirm these are not available to test with engine running?

Edited August 6, 2013 by Vincent Vega (see edit history)

[Guest Mc_Reatta]

- Why would those devices be unavailable to test with the engine running? It allows me to override them.

They are needed to keep the engine running. If they were taken offline, the engine would die.

- With the engine off why do they automatically cycle from on to off?

- All devices appear to be working as I can hear the relays clicking on and off.

You answered your own question. How else could you hear them and confirm they are being commanded on and off. Therefore problem is not with ECM or circuit.

These are the oddities that make me suspect the ECM.

Can someone confirm these are not available to test with engine running?

Look at ECM Data while engine running to confirm what is happening with sensor inputs.

[KDirk]

This sounds more and more like a failed ECM to me. Much like the problems I had with my first 88. Thing is, the ECM almost ever has an outright catastrophic failure. Usually just a portion of it malfunctions, and this instance fits the typical failure pattern.

Often it is bad solder joints, but there are also components in the ECM that burn out due to shorts on external components. The QDM ic's are susceptible to this type of damage.

The OPA3 being so far out of range is also typical of a failed.ECM. Range is supposed to be limited between 0-255 (or FF hex as stored in the ECM RAM).

Anyway, that is my take on it.

KDirk

[Vincent Vega]

Look at ECM Data while engine running to confirm what is happening with sensor inputs.

ECM DATA: values appear to be in range.(OLDPA3 is confusing due to discrepency in FSM and Diagnostics booklet)

ECM INPUTS: shows the Hi/Lo(on/off) values for 6 sensors

I am referring to the ECM outputs.

ECM diagnostics is broken down into:

ECM DATA

ECM INPUTS

ECM OUTPUTS < This shows the value "= = = = =" for every output when the engine is running. It cycles the outputs on/off when the engine is not running

The Question is: Is This The Correct Behavior?

ECM OVERRIDE < I can override the ECM outputs when the engine is running

ECM CLEAR CODES (CODE RESET)

ECM SNAPSHOT

Thanks,

[2seater]

VV,

I have had an odd behavior lately also, so I am very interested in what you find. I never get any codes, but twice in the last month it has refused to idle on it's own. Once was engine cold, the other with engine warm. With manual intervention, depress throttle, it idles fine. I suspected the IAC was having an issue, so I watched what it was doing, or being commanded to do. During the hot incident, the IAC was hunting all around 100 counts, trying to "catch" the engine, but failing to do so, then the issue disappeard on its own during the same drive. The following morning, it started normally, idled up and then slowed down as it warmed, as per normal. IAC counts were in the 130's and didn't drop when fully warm, but it idled fine. This was this last weekend. Now, warm idle counts are in the 50's, and no issues are apparent. I am using a TPI throttle body/MAF assembly, so actual counts may be different than what many will see. Fuel pressure is textbook perfect, and my vacuum/boost gauge shows steady and normal readings. A tap test on the MAF was negative, but I cannot be certain it is not acting up intermittantly. I still suspect the IAC, MAF or possibly the ECM itself.

[Vincent Vega]

Must be a WI thing. Last weekend I moved the car from the driveway to the street in the morning. Late afternoon went to move it back. (In the sun the entire time.) It wouldn't even start. Around 7:30 I went to try again. Started right up. No new codes. No history codes. As a programmer, not being able to duplicate the fault is very frustrating.

[Ronnie]

Must be a WI thing. Last weekend I moved the car from the driveway to the street in the morning. Late afternoon went to move it back. (In the sun the entire time.) It wouldn't even start. Around 7:30 I went to try again. Started right up. No new codes. No history codes. As a programmer, not being able to duplicate the fault is very frustrating.

The next time it won't start pull a spark plug wire off and checkt to see if it is getting fire OR put a small amount of gas into the intake to see if it will start. That way you will know if it is an ignition problem or a fuel delivery problem.

[MarkV]

Guess what I had the same issue last night and it happened with the old ecm as well (code 42). Last time it was a slightly loose spark plug, that threw off the code. The problem is with these things is that it could a 1000 different things throwing off something else that throws off this code. Last night I started having slight driveability problems coming home from work. I parked the car and went back out a half hour later drove to Home Depot and it did not have the problem again. It has not done this in about 4 months and it only does it once and then it is gone. I have new plugs, wires, ign. module, coil, fuel pump, relay, etc. etc.

[Vincent Vega]

ECM OUTPUTS < This shows the value "= = = = =" for every output when the engine is running. It cycles the outputs on/off when the engine is not running

The Question is: Is This The Correct Behavior?

The answer is: YES. This is normal.

Thanks for checking, Ronnie.

[Vincent Vega]

Last summer I replaced the ECM. No difference. Intermittent, random code 42 and dies. About a month ago replaced the Ignition module. 200+ miles and not a code 42 yet. Mileage is better and car runs great.