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Unread 07-11-2011, 06:44 PM   #1
tato1111
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Bad pcm? engine missing when on load.

This is a copy of glassplinter's thread because my jeep is doing the exact same.

The engine surge is like many describe here but different at the same time. It started out when I was driving up hills and tried to accelerate. Everything would go fine and then after about 30mph or so, the engine would start really surging quickly and the whole vehicle would jump, kinda like someone learning to drive standard and can't figure out what gear to go into. Never threw a CEL or anything and never impacted driveability. The problem has gotten progressively worse though and continues to surge when under load. Here's a list of things checked and changed within that time framethings ive changed) Fuel pump, fuel filter, tps, dist cap, roter, ignition pickup, and cleaned all big electrical connectors.

Anyways so i cleaned the harness on the pcm and my jeap ran great, everything worked amazing for about 15 minutes then it went back to surging. could this be a bad pcm or what the **** would cause this? How much would the stealership charge be solve and fix this?

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Unread 07-11-2011, 07:22 PM   #2
Oldfrog
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The trouble with the dealer is that you could pay $1200 or so and it not solve the problem. If you havent swapped the TPS, do so. It's cheap compared to other parts. Make sure the distr cap is tight...because they get loose. While you're at it go ahead and swap the cap and rotor.

No one wants to change the PCM, but it many, many cases......it's the cure. When they begin to go out, they do all sorts of stupid *****.
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Unread 07-12-2011, 01:10 AM   #3
tato1111
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You didnt read what i wrote at all did you? Does this sound pcm related?
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Unread 07-12-2011, 01:19 AM   #4
newfieZJ
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I would say the PCM connection cleaning worked because the PCM was reset . I won't exclude it , but , it doesn't sound PCM relevant .

Don't be mad at OldFrog , you need to use quotations around what you quoted , then be more specific as to what "you've" done . All I see was you cleaning the PCM connection Did you change/check the TPS ?
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Unread 07-12-2011, 01:31 AM   #5
newfieZJ
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I just briefed over "glassplinter's" thread . I hate suggesting parts w/o being sure but I'm gonna say the coolant sensor that sends signal to the PCM .
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Unread 07-13-2011, 01:28 AM   #6
tato1111
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I drove it today and there wasnt any sputtering so idk. i keep us updated.
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Unread 07-13-2011, 02:12 PM   #7
eshew
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Is it s surge or a miss? IF its bucking you might have some bad plug wires.
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Unread 07-14-2011, 06:03 PM   #8
tato1111
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Its more of a miss. and it bucks.
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Unread 07-14-2011, 06:14 PM   #9
newfieZJ
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Is the bucking when your kinda coasting along either in town or hwy ? If your on the gas , does it still do it , or does applying gas matter ?

I had a Dakota 5.2 with that kinda issue . Turned out to be a bushing in the distributor , said the guy I sold it to . I didn't have time to mess with it at that time .
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Unread 07-14-2011, 07:35 PM   #10
Oldfrog
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I did read it. What I'm wondering is....do you think the surging occurs near a shift point in the tranny? You mentioned going uphill....and at 30 it starts doing it. Tranny problems? Or PCM problems and it not being able to process the signal from the tranny properly? ( I am assuming the tranny fluid level is fine).

Resetting the PCM, IS what caused it to run good for a while, btw.

For the record, mine did the same thing once in a while when before I replaced the PCM. Not saying your issues are the same...but I wouldnt let $225 stop me from eliminating it again. It's simply to easy of a fix,....if indeed that's it. If not....you arent broke, as you would be, by using the dealer.
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Unread 07-15-2011, 12:08 AM   #11
tato1111
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It does it at about 1800-2200 anything above that and it runs fine. Doesnt matter the gear. When i reset the pcm it ran fine for about 15min. Its not sending a code eather so its very hard to diagnose. When i hit bumps on the highway it sputters as well.
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Unread 07-16-2011, 06:14 PM   #12
Oldfrog
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Ok, it does it at low RPMs, right? It also does it when you jar it by hitting a bump.

The low RPM thing puzzles me a bit, except for the fact that the PCM needs constant clean power all through the range engine speed. I am supposing your alternator has been tested...? ( sorry for asking)

The hitting of bumps making it act stupid was one of my bad PCM's early signs of failure. But it could also mean there's a bad sensor connection somewhere too. Or maybe a bad ground. I know this is a difficult problem to track down, dude.

Even with my electronics background, it was still a nightmare for me, because the entire system was obviously engineered in a crack house by 17 non English speaking tweakers, in the dark, without a calculator... while 3 hookers grope them at the same time. I've often wanted to redesign mine fro the ground up, but I simply dont have the time. In absence of that, all we can do is to apply as much logic as possible to whatever "constants" it presents us with.

I blame the formation of the EPA for all of these troubles. Abolish the EPA and we can have simple, clean vehicles again, like a 64 Chevy....chuckle..
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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