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Discussion Starter · #1 ·
Hey All, I've had this truck as a plow rig for almost 4 years now. Never let me down and thing likes to push snow. It's run great so far this winter, nothing abnormal.

Recently it blew the O-ring seal off the oil pressure sending unit which I found after seeing a big oil puddle. No big deal to change right? Well during my investigation I moved some of the wires, wiring harness over passenger side valve cover and the connector tree that is mounted to the rear of the passenger side valve cover (haven't figured out what that does yet) to get a little better access.

Well I go to start up next day and thing runs rough. No power, stumbles when I put it into D and dies if I try to give it gas in D. A little investigating pulling plug wires and I'm running on 4 cylinders -- 1 - 4 - 6 - 7 exactly every other cylinder firing. At first I thought something ignition related, but how could I lose spark to 4 cylinders at once? Then I got thinking about intake manifold and if possible 2, 8, 3, 5 are all on one plane off of one injector, so possibly an injector issue caused by fingering those crispy wires previously?? Or is that just pure coincidence and I'm chasing a red herring. Maybe an idle speed circuit? But it should run on 8 once I'm off idle right? My gut tells me it's something stupid that I've overlooked.

Anyways, guess I'm just looking for a place to start. Any input greatly appreciated.
 

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Check your ignition wires for proper firing order: It's 1-8-4-3-6-5-7-2.
 

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If I remember right, up until 1992 with the Magnum engines, the 3.9L V-6 and 5.2L V-8 have a throttle body fuel injection system with only 2 injectors at the throttle body. 1992 and later had multi injection systems, 8 injectors.
Is it possible that you broke or damaged the wiring to one of the two fuel injectors? Can you remove the air cleaner lid and see the fuel spray from the injectors at idle, and see if both are spraying?
Also check fault codes:
 

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You have an injector that isn't working.

The engine is set up as two four cylinder running engines. Given 2 outboard on one side and two center cylinders are running, half the engine is running. Look at the H pattern runners on the intake manifold and you will see this. It is every other cylinder in the spark pattern that is working, and a 2bbl throttle body feeds each of the two runners.

As Bob Lincoln wrote, check the wiring.

Or....

Time for a throttle body rebuild or replacement.
 
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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
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I think that you have an injector down:
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IC, my exact thought. Had a customer with the rather rare Ford TBI 302, it was dead rich on 4 cylinders. I switched the injector wires and it moved to the other 4 cyls. It had a bad computer. I would do a quick swap of the wires to the injectors, if it still has the same 4 dead, then it is the TBI unit, it it switches, it is wiring or computer related.
 
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Discussion Starter · #8 ·
I would do a quick swap of the wires to the injectors, if it still has the same 4 dead, then it is the TBI unit, it it switches, it is wiring or computer related.
Good idea, I'll give this a shot .... but do both injectors pulse at the same time? If they don't and I swap the wires, wouldn't that throw off the timing of the injector pulse for that specific side of the TB/intake manifold & fuel to the cylinders it feeds?
 

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The TBI injectors run on a duty-cycle pulse. I don't think that they are timed.
MPI injectors that feed individual cylinders at the opening of the intake valve are timed.
 

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. . . . The TBI injectors run on a duty-cycle pulse. I don't think that they are timed. MPI injectors that feed individual cylinders at the opening of the intake valve are timed. . . .
Service manual for my 1991 Dakota, 5.2 L throttle body V8, indicates that the injectors are pulsed 8 times per crankshaft revolution during start up. Once the engine is running they are pulsed 4 times per crankshaft revolution. Since each injector feeds into a dual plane manifold with 4 cylinders fed by each plane, no need to time pulses to firing of each cylinder. Pulses timed to every 90 degree rotation of the crankshaft when running.
 

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Discussion Starter · #11 ·
Excellent info, really appreciate it guys. I have some things to try this weekend when the temps warm up:

-check injector wiring back to harness
-check connectors & vacuum hose on the solenoid tree
-swap injector wiring & check running cylinders

Maybe a dumb question here but if it turns out to be wiring related to the passenger side injector and I can't track down the culprit can I just piggyback the passenger side injector harness off the driver side harness since they seem to receive the same pulse from ECM?
 

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Running both injectors in parallel will double the current. This may damage the PCM.
Diagnose this. If a PCM driver is out, it needs a PCM. If it turns out to be a wiring issue, repair the wiring.
 

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Excellent info, really appreciate it guys. I have some things to try this weekend when the temps warm up:

-check injector wiring back to harness
-check connectors & vacuum hose on the solenoid tree
-swap injector wiring & check running cylinders

Maybe a dumb question here but if it turns out to be wiring related to the passenger side injector and I can't track down the culprit can I just piggyback the passenger side injector harness off the driver side harness since they seem to receive the same pulse from ECM?
Again, it only takes a minute to look down the throttle body when it's running to see if both injectors are shooting fuel at idle. That's very valuable information that's quick to obtain with no tools. :)
 
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I had this happen on my 88 10-15 years ago. It was an injector. Swapped and confirmed. Pretty easy fix. Like others have said if you look at it with a flashlight you can see the little mist injecting.
 

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I have used the strobe effect of an advance timing light to see the spray pattern. You can adjust the timing light until the 'cone' becomes visible. Any drops of fuel will show up against the mist.
 
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I have an 89 B250.

The 14 pin connector on the ECM has two fuel injector driver pins.

This 14 pin connector has been quite problematic in my 21+ years of ownership of this van, with my previous ECM having the pins on the solder board needing to be resoldered. I could not find anyone to do this for me, and wound up doing it myself, and it lasted 7 more years before the ignition driver failed in March last year.

your playing with the wires nearest the oil pressure sensor 'might' not have anything to do with this issue. On mine the 8 terminal connector closest to the OP sensor is for the transmission, the neutral safety switch and overdrive/ lockup solenoid, if I remember correctly.

Slight pressure on the 14 wire connector up down or side to side, when mine was acting up, could have it either run one injector, or both, or stall and not restart, or run perfectly. I got away with Zip ties holding pressure on it in such and such a way for far too long, but not long enough. It got progressively worse, and lots of trial and error and zipties were required to complete one stressful roadtrip. Thankfully these stalls did not occur at speed or in very difficult areas to lift the hood and tinker,

I have made a tripod to hold the 14 pin wire bundle immovable in relation to the ECM connector itself, and bought a backup ECM, not only for backup, but for potential future diagnosis.

One thing to note with this 14 pin connector, is not only does the weight of the stiff wire bundle stress the pin/solder connection at solder board, previous techs might have pierced the wire insulation causing the copper stranding to corrode. While the pins and sockets likely still have dielectric grease smeared inside, this does not mean the electrical connections are still good within. I was able to pull what looked like dried flakes of scotch tape out of my connectors.

CRC QED cleaner is good for flushing out old crusty dielectric grease and other detritus, but does nothing for the potential and likely resistance inducing oxidation built up on the electrical mating surfaces of pin and socket.
After the CRC flushing, Caig Deoxit D5 and precision swabs and some den-tek mini bottle brushes allowed me to turn those sandpapery feeling pins and sockets back to polished oiled brass consistency.

Later on I cleaned all sensor connectors with this CRC and Caig D5 combination/ mini bottle brush and precision swab method, and it felt like I removed 500 Lbs of cargo afterwards driving around town. The MAP, TPS and O2 sensor connectors turned the precision swabs blackest.
Caig has a Shield product too, meant to keep cleaned connections free of oxidation. Beware that this product seems to swell the silicone accordian style boots of waterproof connectors, making them very hard to reseat. I'd not use the spray, if choosing to go farther and using this product, but use the liquid and apply with a brush or dip a precision swab.

I am not a fan of pushing tons of new dielectric grease onto pins and sockets then seating the connector. I do apply the Caig deOxit shield, carefully, to cleaned electrical contact surfaces, then seat the connector, then try and force any dielectric grease on any potential entry point of that connector instead.

I know many will say if it still has grease inside the connector it is fine, blow on it, reseat it and move on, but my experience was the opposite.
 

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Discussion Starter · #17 ·
Alright guys, I was able to spend some time on the beast this week. Here is what I did
  • Found a harness schematic for the engine bay and traced all wires and connectors from the main harness to all relays, checked 14 pin connector on ECM. Nothing out of the ordinary.
  • Check & traced all vacuum lines on the solenoid tree. Nothing out of the ordinary that I could see.
  • Remounted the solenoid tree bracket onto the pass. VC. I hadn't secured it very well before. Maybe the solenoids needs a good strong ground through the bracket? Or the vacuum lines need just the right angle to seal against the solenoid? Dunno.
  • Checked all plugs and wires, checked for any cross spark on plug wire routing
I figured I'd check all this stuff before I switch the wires on the injectors.

I crossed my fingers, sent out a prayer to the mopar gods and started up. It fired right off but again lots of sputtering & hesitation. The difference this time is I could put it in D and it would stay running. It would load up & stall out before. This seemed like progress to me .... so I put my foot down and started a couple laps around the driveway. It definitely struggled at first lots of hesitation, surging, missing, but after about 5 minutes without stalling (did an injector thaw out? Idle control motor come back to life?) she started to pick right up and power was completely back. Even plowed a bit with no issue. Idle was great, came right down to a nice idle after giving some throttle. Checked the cylinders and they were all running. Both injectors firing.

I wish I found something conclusive, but all I can think is that if it's fuel related maybe it was bad gas & frozen injector? Or if it was electrical the engine bay warmed up enough to change some resistance somewhere along the harness? More questions than answers I guess and can't shake the feeling that it will return, although I did another cold start after it sat for couple of hours and fired right off.

Anyways, appreciate everyone's feedback. guidance, & diagrams. Hopefully I won't need to come back! Except for pleasure of course.
 

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When I had an injector act up, it was obvious looking into the throttle body with a strong light, and also a finger placed upon it could detect it was ticking differently from the other injector.

Its amazingly easy to pull out an injector and replace, or just swap the caps on the injectors.

The getting better as it warmed up description, reminded me of when my first ECM failed back in '04 or so.

It was a btit weird in that it usually had no problems on the first cold start, but after a short drive then parked for a bit, then restart it would cough and burp and sputter, then boom like a switch was thrown, run perfectly.

Last year when the cardone reman'd computer failed, I threw in the original, and it fired right up. When i tried it again a bit later it did the same frt sputter relay click on and off thing.

I bought both my latest ECM's through Autozone, Cardone remans. I did not bother returning~50$ cores for refunds. One can find the 10% off discount code and they arrived in CA from Pennsylvania i a few days, fedex, For about 216$. Which is cheaper than sending in a unit to a place which rebuilds them.

Its very possible one of your ecm's injector drivers is failing. Capacitors are lucky to last 15 years and you are on year 33, if still original.

I still want to order up new caps and try and replace them on my original ECM.
 

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Discussion Starter · #19 ·
Back to the drawing board. Jumped in it last night and it started right up but still a little sputtering.

Figured giving it some throttle around the yard again would do the trick, except this time it stalled out dead. I was able to restart and limp it back to my parking spot bucking and sputtering. Now it will start right up and sound good for a split second and then drop rpm & die, consistently. If I am quick on the throttle I can get it to rev up but it sputters at higher revs and eventually dies no matter how much throttle I give it.

I'm thinking fuel issue again. I do have an electric fuel pump in the tank that was put in before me so I'll check pressure at the TBI, but I can hear it whirring away.

I believe the injectors fire at double time during crank so maybe once they are out of the crank sequence they aren't getting fuel to intake? Or possibly losing spark after the start sequence? Does the coil get a constant 12v when key is in "run" vs "start" ?

I could see this being ECM related, but I don't think I'm ready to plunk down $200 unless I'm certain. That's 1/5 of how much I paid for it!
 

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Well, again, you can look down the TB at the injectors and see how well they are firing. You could also add some fuel stabilizer/drygas to see if there is accumulated moisture in the fuel affecting it.
 
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