Huge misfire and ensuing frustration SOLVED!

Jimbo955i

Jimbo955i

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Hello everyone, this is officially my first help thread. I’ve owned my 94 Lightning for about a year and a half now, and apart from replacing minor parts here and there, it’s been solid. About a month ago while sitting at a light, it’s started bogging and chugging really badly. That cleared up almost right away, but it developed a misfire to the point it’s not drivable. I found no codes on the reader, active or stored. I’ve replaced the following:
Plugs
Wires
Coil
Cap and rotor
Upper plenum gasket
PCV and hoses
IAT/Coolant temp/O2 sensors
IACV valve
Fuel filter
Injector pintle caps and O rings

Just checked timing and it’s at 12*, although it’s jumping back and forth off the mark a bit.

Checked fuel pressure which shows:
2psi key on engine off
31psi key on engine on
41psi key on engine on with the fpr vacuum off
Bleeds back down to 5psi after it’s shut down with the key on.

Does this on both tanks. It sounds almost like it has a cam and sputters up and down the rpm range. I truly appreciate any insight.
 
Are you removing the spout connector when you check the timing? If not it is concerning that the timing moves when you check it.

The fuel pressure should hold for a while after it's built up. That's a concern as well. Sounds like either a bad pump in one of the tanks or the pressure regulator. Do you notice any crossflow from one tank to the other? There was a recall on that from Ford.

Please elaborate on what you mean by bogging and chugging. Neither of those terms are very specific and you called it a misfire in the subject.
 
The spout connector was removed, and the truck was fully warmed up prior to checking the timing. I haven’t noticed any cross flow from the tanks, and it does the same thing regardless of what tank the switch is set to.
The bogging happened one day, which was the first issue I had. All of a sudden rpm dropped and the exhaust sounded deeper, like a boat engine. That went away immediately, but seemed to be the beginning of it all.
It sputters going up and down rpm. It’s less noticeable while idling, but it’s a big issue under any load. The worst of it is around 2500rpm. It just skips and the best thing I can equate it to is a misfire.
I’ve traced my vacuum lines and haven’t found any to be disconnected or broken. I’ve yet to smoke test it. I was surprised with the lack of fuel pressure with the key on/engine off, but it seems to be holding pressure while on, albeit on the low end of the range. Haven’t detected any fuel coming from the fpr vacuum barb.
 
I would check the fuel pressure while driving to eliminate that issue. Then check the ECM for bad capacitors. We have seen alot of that lately.


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ASAP said:
I would check the fuel pressure while driving to eliminate that issue. Then check the ECM for bad capacitors. We have seen alot of that lately.


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Crazy thing to me is that it starts up quick and strong every time, hot or cold. I thought maybe a leaking injector since the fpr isn’t spraying fuel when the vacuum line is disconnected, and it’s doing it on both tanks.
Was hoping it was an easy fix before pulling the ECM, but it looks like I’ll have to check it.
 
Just for posterity, I fixed my truck by swapping out the distributor. It runs like new again. Thanks for everyone’s help. If nothing else, I’ve replaced parts that were original and bound to fail anyway, and picked up some new skills along the way.
 
ALL parts are bound to fail. Until they do, or they're due on the maintenance schedule, replacing them is a waste of time, money, & effort. And considering that the best parts are factory parts, the longer you use them, the better the truck is likely to run. So scrapping a working original part decreases the truck's reliability.
 
Steve83 said:
ALL parts are bound to fail. Until they do, or they're due on the maintenance schedule, replacing them is a waste of time, money, & effort. And considering that the best parts are factory parts, the longer you use them, the better the truck is likely to run. So scrapping a working original part decreases the truck's reliability.
Click to expand...

Well, if I had known what the issue was that was causing my symptoms, I likely wouldn’t have replaced all of these parts, be it out of ignorance or impatience. I unfortunately took the long way to get there. Most of what I replaced are tune-up items anyway, with the exception of a failed iacv, and thirty year old O2, coolant, and air temp sensors which were replaced with Motorcraft units. I updated my own thread to hopefully help someone else in the future, since many threads (on any forum) don’t reach resolution. Your comment read more like salt in a wound, but that’s cool. I’m just happy to have figured it out.
 
Jimbo955i said:
I’ve replaced the following:
Plugs
Wires
Coil
Cap and rotor
Upper plenum gasket
PCV and hoses
IAT/Coolant temp/O2 sensors
IACV valve
Fuel filter
Injector pintle caps and O rings
Click to expand...
Jimbo955i said:
Most of what I replaced are tune-up items anyway...
Click to expand...
EFIs don't need tune-ups; that's a carburetor term. EFIs only need maintenance & repairs, and the only parts on your list that are on the maintenance schedule are the spark plugs, PCV valve, & fuel filter.

(click this text)

Jimbo955i said:
Your comment read more like salt in a wound...
Click to expand...
Since the purpose of putting salt in a wound is to stop it from bleeding (so it doesn't get infected & heals faster) - yes, the purpose of my posts is to help you stop hemorrhaging money and keep your truck in the best-possible condition. Not to make you feel good about it, or like me. If you ever notice a symptom that suggests an ignition system problem again, follow the diagnostic procedure on this page to pinpoint any faults in that system, without wasting time, money, or effort:

(click this text)
 
Steve83 said:
EFIs don't need tune-ups; that's a carburetor term. EFIs only need maintenance & repairs, and the only parts on your list that are on the maintenance schedule are the spark plugs, PCV valve, & fuel filter.

(click this text)


Since the purpose of putting salt in a wound is to stop it from bleeding (so it doesn't get infected & heals faster) - yes, the purpose of my posts is to help you stop hemorrhaging money and keep your truck in the best-possible condition. Not to make you feel good about it, or like me. If you ever notice a symptom that suggests an ignition system problem again, follow the diagnostic procedure on this page to pinpoint any faults in that system, without wasting time, money, or effort:

(click this text)
Click to expand...
Noted and I appreciate the intention. Live and learn. Thanks for the guidance.
 
Nuts!!! I wish I could have read this last week. I would have suggested looking at the TFI module. That failed on the 5.0L that was originally in the Crown Vic. Had the same symptoms you had. Swapped out the plugs and wires before the real problem was diagnosed. Ironically, a few months later, the engine died anyways. Very annoying!
 
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