93-4.0 fuel pressure issues +- four psi…. I’m a dork

[FEandGoingBroke]

Let's just take a deep breath gents...

@2011Supercab sometimes it's just better to not say anything at all.

@FEandGoingBroke sometimes it's good to start from the beginning and inspect the overall health of the engine by running a full blown compression test. At least you will know the heath of things before going further.

I just have a simple question... what spark plugs did you put in it?

Indeed I did begin by checking the overall health of the engine discovered a water leak repaired that.
Changed old plugs at that time
Wires are 300 miles old, Belden top of the line, excellent fitment, ohmed out perfectly, no loose tips.
Great start up and idle, great free revving.
Smooth acceleration under 1/2” of pedal travel.
Choppy acceleration at anything more.

Coolant temp sensor for gauge was weepy and gauge was inconsistent, replaced with new.

Crank sensor, oily and ugly and old and oh hell sure it could be intermittent, it’s simply a winding of copper wire and a magnet, maybe it was failing, and at 19 or 20 bucks, why not?! No change.

Coolant temp sensor for ecm was sometimes off and gave rich idle when warm as it’s attitude decided, changed out with new.
TPS sensors that fail generally behave this way, replaced with new. (Still under 120 bucks for parts and all the gaskets I replaced)

after all that I came here to pick brains.

furthermore, fuel pressure as explained above operating out of book range when running, also under initial pump up koeo specs within one psi on the low side of book range, thus the new fuel pump. Same results, warranty replacement pump next day, same results with pressure and runability.
Onward to new pressure regulator, more positive results but not by one or two psi. Details five posts ago.

(a gentleman here in the forum suggested these 4.0 motors will still run decent as low as 20 psi)

The only items not replaced as per “runability” are the MAF sensor which is performing exactly to specs as per running tests, and the ECM, which had crap capacitors that I cleanly and diligently also replaced, all to the same results. So the ecm could still be the culprit, but testing it is a skill I have no awares about not a procedure to follow.
Since my TPS is under warranty I’m replacing it tomorrow. Same with the $92 dollar fuel pressure regulator.

I am at my wits end, thus I throw my self on the mercy of your experience and thoughts. I simply could have missed something totally novice but I can’t think of it. So I shall not take offense Any longer at suggestions and perform every test available and suggested by Y’all…. Without producing an attitude! (Probably)

Warm regards,

Gary

 

[FEandGoingBroke]

I’m hearing crickets…. Come on guys you can’t actually have stuff to do between all these silly posts of mine.

 

[Uncle Gump]

Well I'll tell ya Gary. .. that isn't a stellar set of numbers. You have a couple cylinders out of spec. Ten percent high to low. I'd say the old 4.0L is a bit tired. Wil it run... yes. Will it run like new... nope. I would guess you have some valves not sealing up.

But if you're feeling a miss with throttle under load... two weak cylinders certainly aren't helping you.

 

[Uncle Gump]

I have to ask another question here...

Is this a 93 4.0L swapped into an 86 first Gen with the low and high pressure pumps?

 

[FEandGoingBroke]

Good question, my daily driver is my 86 XLT 2.9 ranger I love it deeply!

alas no, this is the original 1993 with a 4.0 but I believe the heads were replaced eight or so years ago.
Standard in tank pump, regulator on fuel rail, edis 6 ignition box and no cam position sensor.

 

[FEandGoingBroke]

Well I'll tell ya Gary. .. that isn't a stellar set of numbers. You have a couple cylinders out of spec. Ten percent high to low. I'd say the old 4.0L is a bit tired. Wil it run... yes. Will it run like new... nope. I would guess you have some valves not sealing up.

But if you're feeling a miss with throttle under load... two weak cylinders certainly aren't helping you.

25 psi compression difference has absolutely no relevance to the engine jerking like it’s losing spark for a few milliseconds randomly, or like an injector refused to open….

mill take a few hours tomorrow to remove the top end and injectors and rest each one. I don’t have a high pressure setup but I have enough pressure to demonstrate squirt and pattern. Perhaps that’s the totality of the issue.

20 feet away is my 1955 gmc3/4 ton that I just got from the Eldridge forest of Endor, it hasn’t run or been started since 1995, the old 248 inline six turned by hand, I threw on a new carb, new battery, cleaned the points with 320 grit wet dry paper, gravity fed the carb, it started up and idled like a sewing machine after a few minutes, and I’m convince that there’s a 4minimum of 30% difference in several cylinders, but it most definitely does mot run like the electrical is cutting off, which is my current dilemma.

 

[FEandGoingBroke]

If the valves weren’t seating properly a blow by test will confirm, but it runs excellent without popping like bad valves do….

 

[Uncle Gump]

I'm not gonna say you don't have another issue Gary... but the results of your compression test are pretty clear. I wouldn't expect it to run like an engine that passed a compression test.

 

[FEandGoingBroke]

OK uncle Gump, but nobody has once accepted point of fact that this is not an overall runnability issue but an electrical interruption in the firing process while accelerating.

My second replacement throttle position sensor should be here within the hour and I will run tests again to make sure everything is functioning properly and report my results for further review from the multitude of brains

 

[FEandGoingBroke]

OK before you guys give up on me and start telling me that my compression is off which causes the ignition to cut out while accelerating I will explain to you what I’ve done today…..

The truck poles tremendously strong and first and second gear and in third gear it’s the pole strong but the cut out of the ignition firing are more prominent in the following three gears.

Today I replaced the throttle position sensor that I had previously replaced with a warranty replacement. I removed the EDIS six, cleaned both connections and put dielectric grease back onto each of the fingers before putting it back.

I cleaned and used dielectric grease on every ground from the firewall forward.

still no codes.

with a raising of hands, who else thinks that the ECM is what’s causing the cutouts in the firing sequence under acceleration?

there are absolutely zero vacuum leaks. The fuel is great, the engine runs smooth as butter in first gear, Accelerate too fast in first gear for the hesitations to show up. And they appear when you first shift to second but only prevalent after half the gear is accelerated through, prominent in 3-5th

 

[FEandGoingBroke]

Aweeeeee schart. I recon I can test the ignition switch to see if it’s sending errant to n off signals while driving, but I don’t have any idea how to pull that off just yet.

 

[rumblecloud]

 

[FEandGoingBroke]

Apparently nobody else does either….

 

[twennydollabill]

Seems to me that you have an electrical signal to the coil pack that's cutting out. Where it get's it's signal I have no idea except it must come from the EDIS6, but that's a part that either works or don't work, never seen one intermittant.

 

[RonD]

Just get an old time timing light and test each spark plug wire for steady pulse and then REV engine and look for missed pulses


EDIS-6 does have a SPOUT Connector, like the TFI, it should be located near the EDIS-6 on inside of Rad support drivers side

Its just a removable connection to disconnect 1 wire
SPOUT wire has the signal from the computer which takes the place of "Vacuum Advance", so its varies spark timing based on engine load
EDIS-6 can do RPM spark advance but not Load Advance it needs the computer to send it that data

Without Load Spark Advance Advance engine will stumble on acceleration, because spark timing is incorrect for richer air/fuel mix
Once you reach steady RPM EDIS-6 has correct spark advance

So find the SPOUT connector and make sure its clean and tight