Performance issue....

U

unity

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I mentioned a couple times that I have an issue with my Mark. I have had the issue for a long time. Started with bad coil packs but never went away. New engine with COP, new tune. Still there...

But I found out something new. Its sporadic. For example, at WOT at almost any speed the car will feel like its missing or timing being retarded something strong. Its bad enough that I feel if I push it too hard it could back fire so I alway back off. Yet one time I am explaining this problem to a friend and go WOT on the highway and hit 110 without even a hint of the issue.

Then the other day I noticed something else. While letting it idle for a long period I noticed that the car would idle rough then something would change and it would idle fine. Then a while later it would idle rough like its missing. I did not have time to measure the times, but I would say that every 5 minutes or so it would go from a rough idle to smooth.

So then I tried something. When idling in drive at a stop sign, if it idled rough I would floor it and soon it would miss or whatever. But if idling smooth, it was fine.

Any ideas? I mentioned before I think the VRCM may be the issue. Could be the computer also. Cant think of much else. Keep in mind there is no EDIS on a 96.
 
I would guess 1 of 2 things. Eaither a bad cam position sensor or a bad crank position sensor. Fords lose the crank sensor very often on their other cars and wonder why not so much on the Marks. Anyway its easy to change and under $20. If you are leaking any fluids on it then its prolly the problem. Only thing is the car usually wont start sometimes or die all together if thats the issue. Cam angle is probable but a PITA to change.

Knock sensor is also a mabey concern.

Best thing to do with the issue you have is to go to a shop that has a real scan tool that lets them read the voltages in real time on all the sensors. Im spoiled and have a buddy with one so IDK how much a shop would charge you to do a read.
 
LaserSVT said:
I would guess 1 of 2 things. Eaither a bad cam position sensor or a bad crank position sensor. Fords lose the crank sensor very often on their other cars and wonder why not so much on the Marks. Anyway its easy to change and under $20. If you are leaking any fluids on it then its prolly the problem. Only thing is the car usually wont start sometimes or die all together if thats the issue. Cam angle is probable but a PITA to change.

Knock sensor is also a mabey concern.

Best thing to do with the issue you have is to go to a shop that has a real scan tool that lets them read the voltages in real time on all the sensors. Im spoiled and have a buddy with one so IDK how much a shop would charge you to do a read.
Click to expand...

Replacement crank sensors had no effect. Cam sensors had been changed too. Was a problem with and without knock sensors, but I will try disabling them again. Already have the tools to scan, but they only say so much. I need a laptop to record anything over a minute and a half.... might just have to do something about that and grab a 15 minute log.
 
unity said:
Replacement crank sensors had no effect. Cam sensors had been changed too. Was a problem with and without knock sensors, but I will try disabling them again. Already have the tools to scan, but they only say so much. I need a laptop to record anything over a minute and a half.... might just have to do something about that and grab a 15 minute log.
Click to expand...

Ahh, didnt know you replaced all that already. I assume you changed the IAC then as well? Since thats always the first thing people check I never ask anymore. MAF clean and reading correctly? How old is the fuel pump? DO you know the fuel pressure?
 
LaserSVT said:
Ahh, didnt know you replaced all that already. I assume you changed the IAC then as well? Since thats always the first thing people check I never ask anymore. MAF clean and reading correctly? How old is the fuel pump? DO you know the fuel pressure?
Click to expand...

I did mention new engine. IAC does not affect WOT. Fuel pump is less than a month old. Pressure reads fine at idle and WOT.
 
unity said:
I did mention new engine. IAC does not affect WOT. Fuel pump is less than a month old. Pressure reads fine at idle and WOT.
Click to expand...

I understand IAC does not affect WOT but it would on idle issues. I also read the new engine but that does not mean new sensors. For all I knew it was a rebuild.
If the engine is all new and the fuel pump is new as well and the MAF meter is fine then that points to a single thing as the problem. ECM.
 
Too bad you can't use somebodys VRCM for trouble shooting.
I know the Kid had one for sale.
Maybe he would let you use it.
Send him a PM.
 
Ok.. um... I will go hunt for an computer and maybe a VRCM. I can see no one has this issue. The only other thing I can think of is that the harness is wired wrong with the COPs.
 
at this point id lean towards the pcm, sounds like it could of been a problem in there all along. its the only thing you haven't replaced. could be a faulty ground driver in the pcm for the injectors, coils etc
 
On 95 and earlier there is an EDIS for spark. The 96 and up lost that, is it all controlled via PCM then? Or does the VRCM have anything to do with it?

It would be great if I could find a PCM with the same EBP2 catch code. Otherwise I have to go through some crap with SCT for my software.

I did check all connections to the PCM and, on the kid's advice, the main engine connector. Cleaned and checked.
 
Oh.. today it backfired when under heavy load at about 30mph only. Pretty sure it was indeed a backfire or something close to it.
 
not sure if the spark is pcm controlled. ford only has online support for 10 years then they drop it, and were not a lincoln dealer so no books on markviii's :(

get a 96 EVTM.......
 
I keep forgetting to look in the book when I get home. But I did find 1996 LINCOLN MARK VIII LSC 4.6L 281cid V8 FI (V) : Ignition : Ignition Control Module on Rock Auto. Several brands listed for 96, and cheap at less than $120.

Where is this thing located if I do have one? I thought under the strut cover, which there is no control module for sure. But I also read under the glove box?
 
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