Leaning out under load???

[Hilljack]

Need help -
Setup -93 OBD1 running 4.6 stroker that was tuned on a dino 10K ago. Ran great until now
Running 24lb Hesco injectors, Hesco FPR, Adjustable MAP

Problem - started missing under load like it was running out of fuel. This started progressively and got worse. At times would get a engine light with code 51 (O2 lean). Note - idles great and revving up with out load just fine.
Pulled plugs - they were so white they looked brand new. (all 6 the same)
Replaced fuel filter, fuel pump and pressure looks good. 36lb and pops up on vacuum, 44 off vacuum. Tried stock FPR and no change. Other parts swapped or tested, TPS, IAT, Coolant temp, MAP with new one and removed adjuster, O2 checks good on bench. Inspected all engine control connectors. Vacuum steady at 17Hg at idle (same since engine was new)

What other sensors could control the injector pulse length?
Cam postition? Crank Pos? I just don't think these are it as it would not idle worth a damn.
Might even look into a donor ECM.
Any ideas would be appreciated

[SkylinesSuck]

If your pump is on it's way out, it very well could show normal fuel pressure at idle, but not flow enough up top. Mine exhibited the same symptoms (back when it was a 4.0) and I pulled the pump to replace it, but when I looked at the filter sock hanging off the bottom, I saw the problem. It was nasty looking. I sprayed the crap out of it with some carb cleaner (since nobody would sell me just the sock replacement) and it was fine after that. Still in there with the stroker now.

[Bodo]

(since nobody would sell me just the sock replacement)

For future reference:

Fuel Pump Strainers (NAPA part numbers):

87-93 XJ / 91-93 YJ = FS0057 DFP
94-96 XJ / 91-95 YJ = FS210 AFP
97-01 XJ / 97-04 wranglers = (two strainers required) FS220 AFP & FS221 AFP

[Hilljack]

Fuel pump and filter were the first to be swapped out. Pressures match between both pumps.
Condition occurs at 1500 to 2000 RPM all the way up. Not an issue that is related to high RPM or WOT.

[Hilljack]

Tried another ECU today with no change.
Also pulled the oil filter and cut it open to see if I had metal from the cam going bad - no metal found. I would assume I would have seen this on a vacuum gauge as well, but did not see an issue there either.

Several questions - what is the best way to test a Crank position sensor and a Cam position sensor on a 93 YJ? I know they are different between some years.
Also, there is some lash in the distributor (1/8 of inch) but no side to side play. Could this be enough to take it out of pulse sinc?

[Hilljack]

Finally got this wrapped up. After spending many hours going thru all the sensors and wiring and browsing forums on line I decided to go back to the simple items and the first was the plugs. Pulled each cap until I got to #6 and no change with the wire pulled. Ah ha something finally pointing at an issue. Put in another plug and everything was good again. That will be the last (Aught to Light) plug I will ever buy. This did not foul out but failed internally over time as this is why the symptoms got worse and the plug was still working when it was first tested. This also explains why the jeep was running lean since one cylinder was not burning and the system was pulling fuel back to compensate.
A lot of time an money to find out it was a $2 plug but glad it wasn't something internal.

[92tank]

mine was doing just the opposite and an injector wasnt working, i tired the plugs first. dont you hate it when its somthing simple that you look over and then feel stupid when you find it. i was about to put the stock 4.0L back in it but im glad i didnt cause it would not have helped.


STUPID STUPID COMUPERS YOU ALWAYS THINK THEY CRAP OUT FIRST!!! OR AT LEAST THE SENSORS

[SkylinesSuck]

Finally got this wrapped up. After spending many hours going thru all the sensors and wiring and browsing forums on line I decided to go back to the simple items and the first was the plugs. Pulled each cap until I got to #6 and no change with the wire pulled. Ah ha something finally pointing at an issue. Put in another plug and everything was good again. That will be the last (Aught to Light) plug I will ever buy. This did not foul out but failed internally over time as this is why the symptoms got worse and the plug was still working when it was first tested. This also explains why the jeep was running lean since one cylinder was not burning and the system was pulling fuel back to compensate.
A lot of time an money to find out it was a $2 plug but glad it wasn't something internal.

Glad you got it fixed! Just FYI, the "system" doesn't figure out a cylinder is missing and pull back fuel to compensate. If you had a wide band, you would actually see the opposite (lean condition) which is counter intuitive I know. 02 sensors read the percentage of unburnt 02 in your exhaust, not the amount of fuel. When a cylinder misses, yes, more unburnt fuel makes it to the sensor, but a much higher proportion of unburnt 02 makes it there too, and that shows as lean. *IF* your computer had a wide band and controlled the mixture, it would see lean, not rich, and dump MORE fuel in to it, not lean it out.