Open loop runs good, closed loop runs bad?

[Expy_97]

97 Expy EB, 4x4, 5.4L

My expy runs good for the first 1-2 minutes after cold start up, but as soon as it goes into closed loop operation is loses almost all power. It has some mild surging during moderate load. it runs worse when i turn on the AC compressor. It runs worse on 93 octane than regular. It runs worse when the ambient temp is warmer. It registers a miss on cyl 8 during heavy load. The engine temp runs pretty solid at little bit below center on the cluster gauge.

It almost seems like the timing is over advanced, but I get no codes other than the cyl 8 miss. I have already replaced all COPs, plugs, and injectors. I have also replaced the COP connector on Cyl 8. Also replaced the cam sensor already, but not the crank sensor. The front o2 sensors have been replaced, but not the rear ones.

I was thinking of replacing the rear o2 sensors. Does this seem worthwhile?

Any other ideas?

 

[toms89]

97 Expy EB, 4x4, 5.4L

My expy runs good for the first 1-2 minutes after cold start up, but as soon as it goes into closed loop operation is loses almost all power. It has some mild surging during moderate load. it runs worse when i turn on the AC compressor. It runs worse on 93 octane than regular. It runs worse when the ambient temp is warmer. It registers a miss on cyl 8 during heavy load. The engine temp runs pretty solid at little bit below center on the cluster gauge.

It almost seems like the timing is over advanced, but I get no codes other than the cyl 8 miss. I have already replaced all COPs, plugs, and injectors. I have also replaced the COP connector on Cyl 8. Also replaced the cam sensor already, but not the crank sensor. The front o2 sensors have been replaced, but not the rear ones.

I was thinking of replacing the rear o2 sensors. Does this seem worthwhile?

Any other ideas?

Since your getting a cylinder 8 misfire I would focus there first. If it really runs better on the low octane fuel would also signify to me the ignition is weak. What is your plug gap set to? The larger the gap the harder it is for the ignition to fire. I would also check compression to see where # 8 is in relationship to the others.

You can try to see what effect resetting the pcm has. This will erase any learn stragedy and it will start fresh.
If the front O2's were bad and you did not reset the pcm it will have to learn from the incorrect values it has already stored.

 

[Expy_97]

Already did those...

I had Ford do a diagnostic about a month ago and they verified that all cylinders were around 140 on compression test.

If I reset the PCM, it will run better for a day or two, but it will eventually relearn to run crappy. I have done this several times.

Plugs were changed about a year ago and I set them all to factory spec.

What else is there to check on Cyl 8 misfire? I already replaced COP, connector, plugs, and injectors. The only thing left is to check the waveforms from the PCM and the triggers but I it only happens under load so I can't even check that in my garage.

 

[Exia]

I had Ford do a diagnostic about a month ago and they verified that all cylinders were around 140 on compression test.

If I reset the PCM, it will run better for a day or two, but it will eventually relearn to run crappy. I have done this several times.

Plugs were changed about a year ago and I set them all to factory spec.

What else is there to check on Cyl 8 misfire? I already replaced COP, connector, plugs, and injectors. The only thing left is to check the waveforms from the PCM and the triggers but I it only happens under load so I can't even check that in my garage.

It could be a ECU problem ( I said could so dont stress ) I would do as Tom said with the plugs the gap could be wrong unless you run +4s or something pre-gaped. Could be a timing issue as you stated, I would run a timing light to check... Also double check you're COPs the could be loose or the spring inside the boot might not me making a connection..

 

[Expy_97]

Agreed

I'm on the exact same page as you. I have been wondering about the ECU for a while now, and that is really the only thing that makes sense with the ambient temp/ 1-2min of good operation. Once the electronics heat up, something is changing. I work in electronics at a semiconductor manufacturer and that sounds exactly like a failure condition. I just wish I could look at the waveforms while I was driving. I could tell immediately.

The plugs were pre-gaped NGK plugs, but I checked every one of them before I put them in.

I can definitely operate a timing light, but how do I connect it to cyl 1 when i have COPs? I haven't done timing on a newer ignition style vehicle. Also, do I have to short out a connector somewhere to get the base timing at idle?

I need to take the COP out of Cyl8 and swap it with another cyl to just eliminate that as a possibility, but i haven't done it yet. I really think the miss is related to a systematic timing issue, which is why i haven't dug into it any farther.

 

[JUST4FUN]

in open loop the O2 sensors are not read by the computer.
you should have a SES light

 

[Expy_97]

in open loop the O2 sensors are not read by the computer.
you should have a SES light

Currently, I only have SES for the Cyl 8 miss, but in the past year I have seen one code for rear 02 Bank 2 heater circuit low come up a few times. I have not yet replaced those rear sensors, but I thought it was odd.

Do the rear o2 sensors affect fuel/air ratio or timing in any way?

 

[toms89]

Currently, I only have SES for the Cyl 8 miss, but in the past year I have seen one code for rear 02 Bank 2 heater circuit low come up a few times. I have not yet replaced those rear sensors, but I thought it was odd.

Do the rear o2 sensors affect fuel/air ratio or timing in any way?

The rear O2's check for converter efficiency only and will set cel when not within parameters. The pcm adjust air fuel ratio based on front O2 readings and over time it stores these corrections into air/fuel tables. This is designed to compensate for engine wear over time. If this is not working properly it can make it run worse over time. A misfiring plug(s), vacuum leak, exhaust leak before O2 sensor, improper fuel pressure can all cause incorrect O2 readings and improper calibration. Another possibility is the pcm needs reflashed as the programming may have become corrupted?! A datalog of various sensors and pids would be invaluable to determine what the pcm is actually doing.

 

[toms89]

Question.

You mention it runs fine in open loop. When exactly does it run well...and then poorly?

Your in open loop on initial start up and basically wot only depending on your specific programming. There is also a variety of conditions that can put it in limp home mode and open loop. Is it stock pcm or has it been flashed with programmer in the past or present?

 

[Expy_97]

Question.

You mention it runs fine in open loop. When exactly does it run well...and then poorly?

Your in open loop on initial start up and basically wot only depending on your specific programming. There is also a variety of conditions that can put it in limp home mode and open loop. Is it stock pcm or has it been flashed with programmer in the past or present?

I have only had the vehicle for about 2 years. The previous owner did not maintain the vehicle at all. It was in very poor condition. I had to fix the exhaust manifolds, collectors, replace cats, front o2 sensors, many vacuum tubes, etc. I have no idea what state the PCM is actually in. I did do a visual inspection of the PCM and saw that there were some rust trails in the vicinity of the PCM, but it did not seem to be on the PCM itself. Also, the PCM had some writing on it. I remember thinking that it probably wasnt the original PCM, but I don't remember exactly what was written on it.

Regarding my open loop comment, I don't really know that it correlates to the open loop/closed loop switch. It runs good when i first start it up for about 1-2 minutes. I correlated that to the approximate time that the engine would switch to closed loop after cold start up. I don't necessarily notice a hard cutover, but it might often happen at a stop sign/stop light. Its hard to say exactly.

 

[bojaz01]

check plugs? mine was missfiring like crazy, when i replaced plugs and wires, the plugs were all gapped btwn .65 and .75......way off what they are supposed to be.....runs like a ***** ape now

 

[Exia]

check plugs? mine was missfiring like crazy, when i replaced plugs and wires, the plugs were all gapped btwn .65 and .75......way off what they are supposed to be.....runs like a ***** ape now

He has plugs and cops..
please try and read the full thread.

Now for the issue, if you can find a use ECU I would try that should beable to pick one up @ a junk yard switch them out see what happens, if the same, than just return. There is no harm in trying

 

[tsgrpr97]

Toms89


Lemme throw this out there...What do you think about too much egr flow? The line going to the sensor with the fixed orifice that measures backpressure/flow (sorry I don't know offhand what its called). If that line is blocked, the pcm will be recieving erroneous data, and the actual egr flow could be much higher than its reporting. The extra egr will be real hard to ignite, but might not necessarily set any codes for mixture.

 

[Exia]

Toms89


Lemme throw this out there...What do you think about too much egr flow? The line going to the sensor with the fixed orifice that measures backpressure/flow (sorry I don't know offhand what its called). If that line is blocked, the pcm will be recieving erroneous data, and the actual egr flow could be much higher than its reporting. The extra egr will be real hard to ignite, but might not necessarily set any codes for mixture.

DPFE Sensor ( Differential Pressure Feedback )

 

[JUST4FUN]

i do know that a temp sensor thinks its over heating it will go into limp in mode cuting fuel by the pcm . you say rust by the pcm i would check the grounds

 

[Expy_97]

Found it...

Looks like one of the new injectors I just installed had a malformed O-ring. I replaced it last night and it seemed to fix the power problem. I can't really explain why it would work for a few minutes, but that seems to have resolved it so far. I reset the PCM after fixing the O-ring, so there is a possibility that it could still relearn to run bad again. I'll give it a week or so and then let you guys know.

Thanks for all the help!

 

[Expy_97]

Continues to run bad

So it took longer this time for the reset to wear off. It is again missing, and running with little power. It seems like the o-rings provided with the injectors were incorrect as they all installed with very little effort. I ordered a full set of o-rings and plan to replace them tonight. We will see what happens after that.