Sexy stroker turned into Bucking Bronco...

[Comanche91]

Just a FYI: I show a code 13 on a OBDI 91 as: No change in Manifold Absolute Pressure (MAP) between engine off and on. Check circuit and MAP sensor.

Did you check the 5V supply input voltage on the VIO wire? How about the output? Sounds like the MAP might be inop?

[Mgardiner1]

Well i've considered the MAP might be intermittent, thats why i have a new one. No i haven't checked the 5v and i probably should. I haven't done that because i'm relying on the computer that it hasn't thrown a code 14 that there is electrical problem with the MAP, while code 13 is a pnematic problem

[Mgardiner1]

Well the new MAP sensor did not affect the problem, as i had not really expected it too. The problem still exists. Only sensor i can see being affected directly by a certian RPM is the crank position sensor. I'm going to dig out my reciept and see about changing it out over the weekend. If that doesn't take care of it, i'll probably start searching for a replacement ECU as i cannot figure any other reason that this problem is occuring.

Its snowing to beat the band up here in the northeast. Its fun having enough motor to break all four 33" tires loose at 20 MPH at 1500 RPM

[Flash]

Get a set of jumper cable and make a ground conection between the (-) bat post and the block.just for giggles.

Bad grounds have coused many a man to when they had replace every thing else first.
It only takes a minute, give it a try...........It probably not the problem but it don't cost you a Dime to prove me Wrong


Flash

[03GC]

Had a similar problem on a 94 wrangler. Had good fuel pressure at idle and when revving engine in neutral, but fuel pressure would drop when accellerating above 3000 in gear.The pickup screen was partially clogged (with mud....oops) and would starve the pump when a load was on the engine. Chased this for about a week. Ended up putting a 8 ft hose on the fuel rail and driving the jeep with a pressure gauge inside(not the safest thing to do,but only way to check under a load).Pressure would drop to 5 psi under wot,then go back up when I let off the gas. I had all kinds of codes popping up(o2 sensor was lean was the one that led me to look at fuel pump more in depth). New pump,screen, and filter cured it. Good Luck
Paul

[Mgardiner1]

Flash, if you saw my grounds, you'd retract your statement. I have the obvious ground from the back of the head to the firewall, Then i have a distribution block for positive and negative. I use 2 gauge power and ground cable (overkill for this lil jeep) looped from the battery, directly to the engine block. I removed the ground from the block the other night, made sure they were cleaned, and the threads for the attaching bolt were bare. I appreciate you being one of the few that are trying to help me, but the answer is definitly somewhere else. If any of you guys could experience this problem.... maybe i just don't explain it well enough.

03GC, thanks for chiming in. I have checked the fuel pressure, and its dead nuts on. I have a wideband O2 in the vehicle as well. If i creep up to 2800RPM with a very light throttle, or mash it to the floor, i get a good 14.7 all the way up until it bucks, and it WILL NOT rev over. It really does act like a rev limiter! If i downshift to get the RPMS over 3000RPM, the 14.7 stays the same and the engine runs like a top! There is an absolute dead spot in the RPM range.

I'll see if i can get some video uploaded tonight

[Mgardiner1]

Here guys, the TAC is really hard to see cause its at night, and youtube quality sucks.... but this is a video of me holding it steady just before and in the problem zone. You can kinda see the tac bouncing if you run it full screen, make sure speakers are on to hear the miss

http://www.youtube.com/watch?v=pstfPHEqtIo



you can hear at the end of the video, how the revs just sneak past the problem zone, and i had to let off a little to get it to miss again.
To re-itterate, it doesn't sound like its popping in the intake, or backfiring out the exhaust
While driving, it is CERTIAN to happen, and happens much more consistantly then it does there in neutral. If you crush the throttle hard enough its really like a REV limiter programed at the wrong RPM

[03GC]

I still wonder if it isnt a fuel pressure problem. If it was a sensor freaking out and dropping cylinders like a rev limiter, would your wideband show lean? Have you checked pressure while its missing or just at idle?
Problems like this suck
Paul

[Mgardiner1]

Haven't had a fuel pressure gauge on it SPECIFICALLY while its missing, but revving with the gauge appeared normal (increase in pressure as vacuum in the manifold drops)

I think i'm going to follow through with my plan, CPS warranty first, then most likely ECU second. I'm waiting for a decent deal to show up on e-bay, i do not want to pay top dollar for a remaned/new one

And yes, the wideband does show lean when its missing. But i think this can be attributed to loss of fuel, or loss of spark.

[Flash]

I use 2 gauge power and ground cable (overkill for this lil jeep) looped from the battery, directly to the engine block. I removed the ground from the block the other night, made sure they were cleaned, and the threads for the attaching bolt were bare. I appreciate you being one of the few that are trying to help me, but the answer is definitly somewhere else.

OK OK, I WILL STOP with the ground idea

Listening to the video............came up with a couple more ideas

Is it possible that the tach is grounding out the coil at that spot on the tach.......would make sence that it runs good above and below 2800

I know that the Renix/4.0(Maybe just the XJ models????) electronic us 4 syl tach signal, weather its was a 4 or a six........Maybe your tach is not compatible in some way............Ya i know, didn't do it before..................

Don't thing it"s fuel related as if it was fuel causing this to happen in Neutral.....it would starve out and dye before you could get moving...........It has to be electrical as the eng is being shut down so sharp.......low fuel volume/pressure would be a slow leaning out and then dying off, not like a switch, like the video is showing.

Do you have a spark tester that loop thur the spark plug(will show spark with out kill that cylinder out???)

Would be interesting to watch the spark while the eng is acting up a 2800 rpm!!!

Flash

[Flash]

I was reading back thur you project thread and there was a wire issue ........of the coil? and that you had drop the coil and had to get a replacement...................Maybe this area need a closer looking into.


Flash

[Mgardiner1]

i've realized something very interesting tonight.....

I started my vehicle, and scraped all the ice off, walked the dog, easily drove to the gas station and scraped off the rest of the ice. Towards my destintaion (vehicle completelyy warmed up, for several minutes), i had NO 2800K problems.

I left my destination 8 hours later. It acted up WORSE then ever. It happened at different RPM ranges and was extremely unpredictible, cold, hot, didn't seem to matter. About 2 miles after it had completely warmed up, the problem went away ENTIRELY. I did not experience one single misfire the rest of the journey home.

Any thoughts?

[SilverXJ]

I would definitely be thinking coil problems. Check the wiring going to it and you may want to try to swap it out.

[Mgardiner1]

yeah? Coil's usually go open when the get HOT. It is a new coil. I'll look the the FSM and see if there are any resistance checks. I didn't unplug it the other night to check the condition of the connection and it seemed ok.

Let me know if you think my theory is correct: It seems to be the computer commanding the coil to stop firing. I say this because last night when it was worse then ever, if i downshifted, the RPM of the engine audibly changed (obviously engine revs higher when downshifting), but the tac inside the vehicle did not rise with it, it fluttered and hunted around 2000 rpm. The tac reads off of the ECU pulse to the coil, so whatever the coil see's, the tac see's. Since the tac was not rising with it, then i'd have to say that the spark was being limited by the ECU.

WHAT SENSORS WOULD CUT IGNITION LIKE THIS??

[bratcop]

I don't yet have enough experience with these motors to offer a specific answer, but I would also bet it is electrical problem, not fuel pressure or the like, as it cuts out so sharply, then returns immediately. Engine operating temp also leads to electrical. I would look at the coil myself. I had an old Honda Interceptor 1000 cycle that would act that way after it got warm( I know, not before but it is similiar), it was the coil. Got any jeep buddies that would let you swap out a coil to eliminate that as a possible problem? Can you pull plugs (or via any other method) and see if one specific cylinder is causing the problem? Probably not the problem, but could one of the plug wires be grounding out on something? Or the coil wire? Good luck...