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  #21  
Old April 15th, 2013, 01:18 AM
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Chris Davis
94 NAS D90 6.2LS
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Yes-- ran it totally disconnected with same issues. Also checked diodes since I had it out for some other work-- they checked out fine too (already ruled out alt when symptoms were present with it disconnected.
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  #22  
Old April 25th, 2013, 10:17 PM
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Chris Davis
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ARGH! So FN Frustrating.

I have Rovergauge running--everything looks pretty good. The right bank lambda is reducing a little, about 20% quite often while the left isn't. Everything else looks great. The truck is running much better but when going up hill under basically full throttle, after going up hill for about a minute, the truck starts buckling, sort of like fuel starved or engine missing. When I use the Mallory coil without the ballast resistor, it gets way worse--I have gone back to standard coil and ballast resistor and it is much better but still does it. It leads me to believe it may be ignition, but I am not ruling out fuel.

The following have been thoroughly tested and swapped between cars and is definitely not the issue:
TPS Sensor
Stepper Motor
Coil
Ballast Resistor
Alternator (ran truck with completely disconnected)
No vacuum leaks
new alternator vacuum advance
ECU. I have 3 of them. Same issue with all.
Fuel rail and injectors and fuel pressure regulator(all changed, same issue)

The following are up in the air:
Speed Sensor (not sure this should even affect anything when going 60)
MAF (on rovergauge it looks good)
O2 Sensors (again, on rovergauge, they seem to be active at least)
Fuel system. Maybe a purge valve or something like that?

Here is another symptom--maybe unrelated,--when I leave the key in the "on" position without the car running and leave it for a few minutes, it floods. I can also trigger the rovergauge to cycle the fuel pump (it sounds fine) and the truck floods.

What this means to me is something isn't behaving right possibly with the fuel return. I am not that familiar with this system but am a quick learner, so this may be related... Any insight?
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  #23  
Old April 25th, 2013, 11:02 PM
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Ian Gregory
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Blocked fuel filter or failing fuel pump? Have you tested your fuel pressure?
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  #24  
Old April 27th, 2013, 03:59 PM
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Chris Davis
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I picked up a Harbor Freight fuel line pressure testing kit (nice piece of gear, btw) and the fuel pressure seems great--right in the 32-35 range. I didn't drive it while it was attached, but I may try that next. I did rev the engine and it stays where it should. I changed the fuel filter while I was at it but I have not had much of an opportunity to drive around. Last night I blew out my right knee jumping down from a retaining wall--MRI on Monday, so I can't tinker or drive for a while (at least not the D90). Once I figure all this out, I will post up what it was... If I can figure it out...
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  #25  
Old April 27th, 2013, 11:55 PM
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Neill Thornton
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This is a 94, right? You know I had a strange issue like this on my series back in the day, and it all went back to the distributor and the points/pickups for the ignition.

Considering you can affect the results by messing with the coil, you have effectively reduced the problem down to an ignition issue. There is an amplifier module on the side of the dizzy that could have gone bad, or perhaps the pickups are failing?
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  #26  
Old April 28th, 2013, 01:09 AM
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Chris Davis
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I'm running a mallory distributor and not only does the e-spark module seem to check out fine, but I swapped in a spare and same thing persists. It's a bugger of a problem, very elusive. I'm no stranger to cars/engines and this one is a challenge...
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  #27  
Old April 28th, 2013, 04:06 AM
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Almost wondering whether the symptoms are going to have to get really bad before the real culprit comes out of the shadows.
Did you modify the ECU after going to a 4.6?
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  #28  
Old April 28th, 2013, 09:54 AM
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Chris Davis
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Yes-- it has a custom mapped chip from Pendy. I've tried other chips-- a 4.2 cold prom as well as stock.
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  #29  
Old April 30th, 2013, 03:25 PM
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Chris Davis
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So not the fuel filter, not the fuel pressure, nor any sensor that I have been able to figure out. The symptom, which is a "stumble" only occurs under load. I would say it is rather like a bucking but can't quite tell if it is lack of fuel or lack of spark. Doing some reading and one possibility that is worth considering is a "weak spark" but the problem persists when using my standard coil (with ballast resistor) or a Mallory coil that doesn't require a ballast resistor (which seems to make everything worse). Although I have no great reason to suspect my ignition switch, I am not going to rule it out as sometimes that can cause an intermittent voltage to the coil which could cause stumbling, but I can't imagine why that would rear its head just when under load. My spark plugs look great and the gap is all correct, I have new Kingsbourne wires (and this also persisted with my used Magnecor wires which were probably just fine), multiple ECU's, new gas....blah blah blah...

So, I am going to swap in some different spark plugs and am in the process of redoing my ground wires and checking all my wiring. Might even throw in a new ignition switch as I just ordered a bunch of parts from one of my european friends where they are just a few bucks. I am going to use the other Mallory coil since all the symptoms were worse with it--it might make catching the culprit easier. This one is illusive...
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  #30  
Old May 14th, 2013, 10:40 AM
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Chris Davis
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Wow, what a journey. I know more about diagnosing just about every sensor and electrical component on the truck than I ever did before. None of that helped me, but I did figure out the problem (90% sure--drove 70 miles, no issue). It was the coil hook up, but I can't really explain why and it was trial and error that finally presented itself.

To sum it up, the wiring instructions from Mallory on the unilite coil say to run the ignition wire and the red wire to the ballast resistor and then hook the ballast resistor to the coil. Which I did. What solved the problem was to run the ignition wire to the ballast resistor (and then to the + coil) and run the red wire from the distributor directly to the coil. Why? Don't know.

What is strange is that I tried the Mallory 30451 coil which does not take a ballast resistor (Neil and others are running this set up) and that made the problem worse than anything.

I can't explain it other than the distributor does not like to be fed the 12V--it likes to get it's power after the ballast resistor. No clue why, don't really care as long as it is stable now...
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  #31  
Old May 14th, 2013, 03:24 PM
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Chris Davis
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I don't have an ignition amplifier with the Mallory Unilite. It has an e-spark module and I did try two different ones...
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  #32  
Old May 16th, 2013, 10:09 PM
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Chris Davis
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I was totally wrong. Whether by fluke, or what, the problem (although much less often) still exists because the @#!@$# truck did it again. I can see why people sell them (then either regret the sale or try and find it). Cause intermittent faults can drive you insane.

My last, possible thought is that it is the fuel pump going out. Why would changing the coils cause the problem to get worse/better? Well maybe it is either a random act of who the hell knows what or possibly a signal gets related on the firing to the ECU to "turn up" the pump and that creates a short/failure. Maybe? Who the hell knows. I just want to take a sledgehammer to the damn thing.
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  #33  
Old May 16th, 2013, 10:25 PM
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Jay Geaney
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You stated that you were going to replace all the grounds. Did you complete that? This whole issue still sounds like a ground fault to me.

Cheers
Jay
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  #34  
Old May 17th, 2013, 12:48 AM
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Chris Davis
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Yep-- I thought so too,. Even ran a new strap from engine to cassis and cleaned battery to tranny cable.
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  #35  
Old May 17th, 2013, 09:16 AM
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Chris Davis
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Brainstorming last night and one thing I have not checked yet is the Fuel Pump Emergency switch (inertia switch)--has anyone heard if that could cause an intermittent stumble? I'll check that before fiddling with the fuel pump--doubt that is it, but easy to check compared to fuel pump.....
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  #36  
Old May 19th, 2013, 01:57 PM
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chris
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I would try two things first ...put in a fuel pressure gauge and tape it to the window and get youself a spark tester make an exstened lead and put it out side the hood so you can monitor.....what your loosing when it stumbles via spark or fuel pressure ....then work from there just my .02
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  #37  
Old May 21st, 2013, 10:42 PM
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Chris Davis
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The truck is still being an ass. I hooked up a dwell meter to the neg side of the coil and I can see that I am loosing dwell when it happens. It has happened at very low speeds, high speeds, low rpm's, mid rpms, typically but not always under load. If I don't change a thing while it is happening (such as the accelerator pedal), I can usually get the condition to persist. let off the gas or push in the clutch and rev the engine, it gets better. It never lasts more than a few seconds. With the dwell taking a dip when it happens, it leads me to believe that the engine or injectors are getting a signal to shut down. My ignition switch is fine and I can't find anything wrong with the wiring. My grounds are great--I have triple check them and run some more. I have also soldered just about every connection and tested them and all seems good. Just checked my unilite module again and it is solid although I suppose it is possible it is hiding something and I have another on the way just to check out and keep in my spare box. I run Rovergauge and my 02 sensors seem to be functioning and I am not throwing any codes, possibly because it is so intermittent. My TPS and my spare both seem solid. My fuel pump has been checked out and is solid (changed it). Swapped coils, ballast resistor and same thing persists. Disconnected vacuum advance in case it was getting too much advance--no change. Typically happens once engine is warm, so it is a pain to really figure out. Plugs looks great. No vacuum leaks. Doesn't stall. When I install "premium" coil, such as the mallory 30451 which doesn't take a ballast resistor, the problem was much worse, which leads me to believe it is spark/ignition related...

I'll try a new ignition module--it should be here by weeks end. Any other ideas? I know it is either shutting off the injectors or shutting off the spark, but why oh why!!!!
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  #38  
Old May 21st, 2013, 10:43 PM
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What haven't you swapped?
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  #39  
Old May 21st, 2013, 10:54 PM
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Craig
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I am guessing you have checked your camshaft and timing...set right?

I trust you don't have the same issue I had....chased down most of what you have over two weeks, and finally found a failed lifter....yup - brand new hydraulic lifter (only one) failed. Was not rising the rocker arm at all - ground the camshaft and the lifter.

New ones on the way.....
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  #40  
Old May 21st, 2013, 10:54 PM
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Greg Liebig
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Mine was having similar problems. Bucking around like crazy and stalling. Put in new spark plugs and everything has been good the last couple of days.
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