Please we could use some help to diagnose whats wrong with the supercharged 93 Mark

Don Pfau

Don Pfau

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A little over a year ago my 1993 Supercharged Mark VIII started taking moments that it would spit and sputter a little while cruising and occasionally stall at a stop. The problem comes and goes but keeps getting worse. We have replaced the Crank, MAFS, and Cam sensor. We even replaced the electric fuel pump even though fuel pressure has always held good at 50-60lbs ?? But it actually ran good for a little while after that but the problem quickly came back and even worse. We have checked all the grounds. pulled and cleaned the computers SCT chip. Changed plugs a couple time. Checked a lot with carb cleaner looking for a intake leak. No codes. All Sensors checked are reading normal. Any Ideas ????
 
Is it possible to do data logging on these cars? If so that would be your best bet as it is an intermittent problem. Sensors and controllers that test good at idle many times will fail intermittently under load. Especially on forced induction cars. Let us know how you make out.
 
Just ideas
Coil pack or packs (screaming deamons are only $100 a pair)
Fuel pressure regulator
Failing ecu
Run a fuel pressure gauge while driving the car (tape it to windshield).
I assume IAC has been cleaned and tps voltage checked?
Also check the crank position shaft wires.
 
Did you check for codes with or without the chip?

You may want to get a breakout box and/or the Rotunda EEC-IV monitor.
 
slowmkviii said:
Coil pack or packs (screaming deamons are only $100 a pair)
Fuel pressure regulator
Failing ecu
Run a fuel pressure gauge while driving the car (tape it to windshield).
I assume IAC has been cleaned and tps voltage checked?
Also check the crank position shaft wires.
Click to expand...
Thanks, It has Screamin Demon coils on it. Yes it has been driven a lot with a fuel gauge taped to the windshield. Pressure is always good even when it does it. Could the regulator still be part of the problem ?? The tps voltage has checked good so far. No the IAC hasn't been touched. I have also suggested that a couple times. I also suggested checking the crank sensor plug and wire. (I've heard that mentioned)
 
Don Pfau said:
Thanks, I have no idea what that is. Would you mind explaining a little for me ??
Click to expand...

The breakout box resembles an old time switch board with pin jacks for each of the wires going to the PCM. It is plugged in between the PCM harness and the PCM. This allows you to use a voltmeter or scope to analyze signals at the coresponding pinouts. I have used it only a couple times. It is sort of awkward since the PCM on the Mark VIII is on the drivers side.

EEC-IV_breakout.jpg

The EEC-IV monitor is a Rotunda diagnostic black box which plugs in the same way but intercepts the signals. Problem is finding one with the Mark VIII 'overlay'. I scored a monitor off a friend but never did find the required overlay and accompanying instructions.

EEC-lV_monitor.jpg


It sounds as if your symptoms are intermittent and under load - hence the need to be able to test or monitor "live", not unlike data logging with OBD2.

EEC-IV_breakout.jpg
 
i also suggest the iac and clean the throttle body while your at it. my car was acting that way about a year ago and i couldnt afford a new iac so u used this.
http://www.zorotools.com/g/00039908/k-G1352145?utm_source=google_shopping&utm_medium=cpc&utm_campaign=Google_Shopping_Feed&kw={keyword}&gclid=CJLf9ojSk7sCFc9cfgodxFIAhQ

and thoroughly cleaned the T.B and ran some seafoam through it. it hasnt acted that way since
i went by this if it helps any http://www.explorer4x4.com/iac.htm
 
driller said:
The breakout box resembles an old time switch board with pin jacks for each of the wires going to the PCM. It is plugged in between the PCM harness and the PCM. This allows you to use a voltmeter or scope to analyze signals at the coresponding pinouts. I have used it only a couple times. It is sort of awkward since the PCM on the Mark VIII is on the drivers side.

View attachment 828463918

The EEC-IV monitor is a Rotunda diagnostic black box which plugs in the same way but intercepts the signals. Problem is finding one with the Mark VIII 'overlay'. I scored a monitor off a friend but never did find the required overlay and accompanying instructions.

EEC-lV_monitor.jpg


It sounds as if your symptoms are intermittent and under load - hence the need to be able to test or monitor "live", not unlike data logging with OBD2.
Click to expand...

WOW, Thanks Driller
 
driller said:
The breakout box resembles an old time switch board with pin jacks for each of the wires going to the PCM. It is plugged in between the PCM harness and the PCM. This allows you to use a voltmeter or scope to analyze signals at the coresponding pinouts. I have used it only a couple times. It is sort of awkward since the PCM on the Mark VIII is on the drivers side.

View attachment 828463918

The EEC-IV monitor is a Rotunda diagnostic black box which plugs in the same way but intercepts the signals. Problem is finding one with the Mark VIII 'overlay'. I scored a monitor off a friend but never did find the required overlay and accompanying instructions.

EEC-lV_monitor.jpg


It sounds as if your symptoms are intermittent and under load - hence the need to be able to test or monitor "live", not unlike data logging with OBD2.
Click to expand...

If I was faced with having to figure out how that works vs scraping the car i'd scrap the car. :confused:
 
Thanks for the help. Well three years later and we finally fiquired out the problem and it was self inflicted. It use to have a custom made guard around the conical air cleaner. At some point my nephew removed it and forgot to replace it. The air intake is in front of the radiator and it appears the guard is needed to get the right air flow signal from the MAF. i could write pages about the grief this caused over a 4 year period. A very humbling experience for quite a few of us here. BUT THE MARK VIII IS RUNNING GREAT. AND IS AGAIN VERY FUN TO DRIVE ANYWERE.
 
slowmkviii said:
Awesome to here it's running good again.
Time to get it running faster thankless kirks.
Click to expand...

17 degrees of timing in hot air....both of those things are going to change along with a couple more tricks. It's getting a hot lava tune on the switch chip with more timing. I want 10s and have every belief it will hit that if it doesn't blow up. The E85 is working very well. I fear that massive tq spike from the corn will begin to beat things up before knock ever does. I'm willing to bet 5 more degrees and it still won't knock. My meth actually quit spraying it's working so well.

I'd actually be curious to see Don's car on corn. It would pick up a ton.
 
First again congratulations Kirk, Now that happy days are here again for me also and I can try new thing to improve the Mark VIII instead of stuggling to get her back. I think i may have a few more tricks to try out.
 
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