Rough Idle, Missing, Pulling my hair out.

[DasBaldDog]

Okay,

Went and drove around for about 15 minutes.

Pulled it back in and 111's all around.

KOEO and KOER both 111's minus the time I didn't goose it and got the 538.


One of the times I did the KOER I didnt slam my foot down during the Goose and got Code 167.

 

[MrShorty]

It looks like there is an Orange wire with a yellow stripe and a Purple wire with a yellow stripe.

Purple/yellow and orange/yellow could be for the 3-4 shift solenoid and the torque converter lockup clutch solenoid. Does the connector look like it could reach over to the transmission?

Now we wait to see if hooking everything back up gets us back to 111.

 

[DasBaldDog]

Purple/yellow and orange/yellow could be for the 3-4 shift solenoid and the torque converter lockup clutch solenoid. Does the connector look like it could reach over to the transmission?

Now we wait to see if hooking everything back up gets us back to 111.

If that 3/4 shift solenoid is only in an Automatic, I have a manual.

And the connector is on a 2 inch leash from the main harness, so it would definately not reach the transmission.


Well, I drove the truck last night for 15ish minutes and got codes 111.... its not my daily driver (especially in its condition) so I only drive it when I have to.


And FIND, sorry I didn't respond earlier, I appreciate that you'd like to help that badly.




What I would like to do is set some sort of baseline for performance, that way I can tell just how much "get up and go" I have lost.... or if even this miss is just at idle and the rest of its performance is perfectly normal. I wonder if I am becoming a hypochondriac about my truck. You know, maybe the miss is at idle and nowhere else and I am worrying about nothing?



One thing that has me thinking... when I first did the KOER test, why didn't I get the O2 Sensor Not Hot, Coolant Not Hot, Didn't Goose Throttle... codes. I should have gotten them, yeah?

 

[MrShorty]

If that 3/4 shift solenoid is only in an Automatic, I have a manual.

And the connector is on a 2 inch leash from the main harness, so it would definately not reach the transmission.

It seems that a lot of "dead end" harnesses like that are intended for uninstalled options. So maybe you are looking at something like that.

One thing that has me thinking... when I first did the KOER test, why didn't I get the O2 Sensor Not Hot, Coolant Not Hot, Didn't Goose Throttle... codes. I should have gotten them, yeah?

Kind of hard to say, because I wasn't there. Only you would be able to say for sure if you neglected the goose test and the engine was cold enough to trigger the O2 sensor and temperature sensor codes. However, it reminds of a time when I was getting a rich code from a car. As part of our diagnosis, we did a few things to try to force a lean code (vacuum leak, unplug O2 sensor) and we couldn't get the PCM to set a lean code. This eventually led us to decide the PCM itself had failed, which, upon replacing the PCM, proved to be the case. I guess in regards to the KOER test, if you neglect something from the test that you know should trigger a code and it doesn't that might tell you something about the situation.

 

[DasBaldDog]

I definately didn't goose it, and the truck was stone cold when I started the test...

Will do it again tomorrow to see if I can get the codes, if not it may be PCM/ICM time.

Crap.

 

[DasBaldDog]

BTW: I can only tell the miss when the truck has warmed up and the RPM's slow down to below 600. Even then I can only perceive a slight shudder of the motor, but if you lean your ear to the exhaust there is an inconsistent "cough" from the tailpipe.

I mentioned the other major symptom of the hesitation upon punching the throttle.

 

[Roadrunner777]

BTW: I can only tell the miss when the truck has warmed up and the RPM's slow down to below 600. Even then I can only perceive a slight shudder of the motor, but if you lean your ear to the exhaust there is an inconsistent "cough" from the tailpipe.

I'm not going to say that's normal, but I know a lot of people here trying to get to a smooth 600 RPM idle... myself included. The last hint I read, something I hope to complete tomorrow, is to change back to stock double platinum plugs and squeeze the gap from the spec .054 to .049. There is some thought that the coil pack is a little soft at idle. And, it kind of sounds like it to me.

Hesitation, I will have to go back and look at what you have done. The top three things, I know you have already checked those.

 

[DasBaldDog]

I'm not going to say that's normal, but I know a lot of people here trying to get to a smooth 600 RPM idle... myself included. The last hint I read, something I hope to complete tomorrow, is to change back to stock double platinum plugs and squeeze the gap from the spec .054 to .049. There is some thought that the coil pack is a little soft at idle. And, it kind of sounds like it to me.

Hesitation, I will have to go back and look at what you have done. The top three things, I know you have already checked those.

Let me know if that shortening of the gap does anything.


What were the top 3 things you were thining of? I don't mind redoing stuff to verify.

 

[Roadrunner777]

If the computer is happy, then I would revisit vacuum and fuel delivery. If you have not replaced the PCV valve, I would do that. It's cheap and it's a vacuum component. Do you know how to post video? If you can do it easily, I'd like to see the vacuum gauge when you punch the throttle.

Another test point I might do is to remove the O2 sensors temporarily and try punching it again. I'd like to rule out flow issues in the catalytic converter.

We are also kind of dancing around the engine computer, ignition module, and coil pack. But truth is, they are candidates for these issues. But, they are going to be expensive, and not easy to test. Just keep that in the back of your mind.

 

[DasBaldDog]

If the computer is happy, then I would revisit vacuum and fuel delivery. If you have not replaced the PCV valve, I would do that. It's cheap and it's a vacuum component. Do you know how to post video? If you can do it easily, I'd like to see the vacuum gauge when you punch the throttle.

Another test point I might do is to remove the O2 sensors temporarily and try punching it again. I'd like to rule out flow issues in the catalytic converter.

We are also kind of dancing around the engine computer, ignition module, and coil pack. But truth is, they are candidates for these issues. But, they are going to be expensive, and not easy to test. Just keep that in the back of your mind.

I have replaced the PCV. I should probably look at testing it regardless.

I can post video, will try and do it tonight. Will need the wife's help.

It is not a blockage in the Cat cause flow to the tail pipe seems excellent and the cat is brand new.

I realize that it could be the icm or PCM. Autozone says they can check the icm, buri need to remove it first and that's easier said than done.

I'm also faulty sure it's it the ignition coil as I swapped a brand new one in and saw no improvement. same symptoms.

 

[Roadrunner777]

Octane jumper installed? If it were not, well, it matches the symptoms, but it should also throw a code.

 

[DasBaldDog]

Octane jumper installed? If it were not, well, it matches the symptoms, but it should also throw a code.

It is installed, but what code would it throw? Perhaps I will remove it and see if there is a code produced. it may line the coffin of the PCM/icm.

 

[Turdle]

If this engine has egr, the mystery plug is indeed for a cam sensor. Some 93 engines do not use this, but I think you do need it if the harness has the provision for it.

You can check this by looking over the wiring diagrams for your specific PCM, and look for the cam sensor in the wiring. Then, check the wire colors listed for it.

However, having been thru all 3 configurations of 93 4.0, I can tell ya the only plug between the 2 02 sensors is for the cam sensor.



Anyone have access to this diagram?

 

[DasBaldDog]

If this engine has egr, the mystery plug is indeed for a cam sensor. Some 93 engines do not use this, but I think you do need it if the harness has the provision for it.

You can check this by looking over the wiring diagrams for your specific PCM, and look for the cam sensor in the wiring. Then, check the wire colors listed for it.

However, having been thru all 3 configurations of 93 4.0, I can tell ya the only plug between the 2 02 sensors is for the cam sensor.



Anyone have access to this diagram?

No EGR.

 

[Turdle]

No EGR.

All 94's have egr. it must have been removed?

 

[DasBaldDog]

No EGR.

As I put in another post, based on a few sensors being different, I believe the engine is a left over from 93. There isn't any evidence of the EGR being removed, just simply not there. The ECT for example is a 93 model abd the 94 doesnt fit.

 

[Turdle]

Does the harness have plugs for egr?

I guess I am having a hard time following ya, but a 93 engine will not work with a 94 harness. That is what I understand you have.

 

[DasBaldDog]

Does the harness have plugs for egr?

I guess I am having a hard time following ya, but a 93 engine will not work with a 94 harness. That is what I understand you have.

There is no Cam Position Sensor where it should be, there is no evidence of an EGR system, and the Coolant Temp Sensor connector only works with a Sensor that Autozone has logged in for working for a 93.... the 94 sensor has a different plug.

So I am assuming that the engine, and harness are leftovers from the 93 surplus. The truck is stamped from Jan 1994.





I pulled the ICM and Autozone ran it on their machine until it got hot and it kept testing good.


In other news, I tried to get the video for you Roadrunner but my vacuum gauge is shot (reads a constant of 11 psi even when off the vehicle). Gonna get a new one this weekend.... but it makes me wonder if it was working right before...



On the ICM/PCM note, is there anyway to test the PCM? A replacement is $200+ and is non-returnable.... so I'd really rather not go that route without proving that the current PCM is bad.

 

[DasBaldDog]

Okay.

Got a new vacuum gauge... thank you Harbor Freight and your rediculous return policy....

Anyways, still reading 19-20"hg with the occasional dip down 1/2 an inch whenever the engine decides to slow a bit.



In side news, while I was shooting this video, the exhaust started to smell of sulphur.

 

[MrShorty]

is there anyway to test the PCM?

"standard" test for a failed PCM is usually process of elimination -- if everything else tests good, then the PCM must be bad.

the exhaust started to smell of sulphur.

This is usually an indication that the engine is running rich. Did we ever have you test the fuel pressure?