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swamp dog 05-08-2013 10:11 PM

94 wrangler bucking & backfireing under accelaration
I have a 94 wrangler that runs ok under light acceleration. When I put under hard aceleration, it bucks and backfires. I have replaced the ECM and all electrionic sending units. I have taken off all grounds and sanded clean. My neighbor thinks it is getting fuel. Once the vehicle warms up and I shut off; it takes quite a while to re-start, almost like it is not getting gas. Also replaced in tank fuel pump. Any suggestions????

AZ WRANGLER 05-09-2013 09:36 AM

Did you replace the TPS?

wrangleryj90 05-09-2013 09:39 AM

Check timing would be my guess that it is off a bit

revjonesy 05-13-2013 03:05 PM

Does it do it when it rains? Mine does it every time we get a hard rain. Water getting into something.

Lil_town 05-14-2013 01:31 AM

+1 for tps my coworker was a mechanic for 20 years he said check the output of the tps sensor with a mulitmeter, should show a nice gradual increase, if there are any stumbles in the readings replace the tps.

Keymo 05-14-2013 04:25 AM

Not arguing on the TPS... Would be good to check as well. But in addition...


Originally Posted by wrangleryj90 (Post 3736971)
Check timing would be my guess that it is off a bit

x2.. Incorrect timing will make 'er hard to start and cause stumbling under hard acceleration - at least I've experienced it before... You might also want to make sure that your Distributor is hooked up to the right vac. source and that the vac line and diaphram are in proper working order...

swamp dog 05-14-2013 06:11 AM


Originally Posted by wrangleryj90 (Post 3736971)
Check timing would be my guess that it is off a bit

How do you set timing on this engine? Distributor is not adjustable.

Keymo 05-14-2013 06:22 AM


Originally Posted by swamp dog (Post 3753856)
How do you set timing on this engine? Distributor is not adjustable.

Haha! I guess it WOULD be important to know what engine you're running... That's why I wasn't arguing with the TPS and also agreed with the timing...

You should fill out your profile or include your Jeep's information in your original post in the future...

Keymo 05-14-2013 06:53 AM

Alrighty... I was hoping to get a response on what engine you're running... Buuuut... I'm really bored right now...

Is it throttle body or injected?

If it's a throttle body - have you checked it/cleaned it recently? What about the IAC?

You said that guy THINKS it's getting fuel? How did you check?
Did you check the actual fuel pressure itself? Your problem could come from improper fuel pressure or the fuel pump not behaving as it should.

Have you happened to check the exhaust system? Sometimes something loose in the exhaust system can cause "blockages" under heavy acceleration.

Also, you said acceleration... Is this only under load? Or can you just be sitting in Neutral and give it hella' gas and then it'll backfire?

swamp dog 06-04-2013 04:59 PM

I have r eplaced the head, fuel pump, ecm. Everything electrical has been replaced. I tested fuel pressure and it is in range. I checked cylinder compresson and it is consistant. It does not backfire; idleing, just under load. When engine warms up it is hard to start. Spometimes I feel it is a fuel issue and other times I feel it is a firing issue. The only thing that I cannot get to work is the temp. guage.

Keymo 06-13-2013 11:29 PM

Sorry this is late - I've been away on vacation...

Do you have the stock thermostatic fan? And if so - Have you checked it to see that it isn't siezed?? With the engine off you should be able to move it pretty easily (like on finger, easy) for a little rotation... If it's hard to move or you can't move it without it turning the pulleys as well, then that just might be your problem.

My J-truck's was bad and I had "bucking" under load and I felt the same as you did initially... But then one day I happened to try to turn it to get to something and she was stuck. I replaced it just knowing that, that was not supposed to be that way and THEN found out that she was bucking because it was siezed up. When I replaced the fan it all stopped.

Just an idea! :thumb:

2fastc 06-16-2013 09:07 AM

i would check for a vacuum leak. get a can of carb cleaner and spray around the intake with the engine running.

Nica_Dom 06-16-2013 02:39 PM

i have a very similar problem with my 94.

around my area in nicaragua where there is no paved road it does great, but when i go for the 2.5hr trip to the capital and hit the paved road, it starts to buck and backfire after its warmed up... if i turn the engine off and wait a few minutes it goes back to normal and i can drive another 25-30 minutes but then again have to stop.

We checked the fuel filter and it was fine, also the intake is on there solid... not sure what it is but i cant afford to take it to a mechanic around me because they might do more damage than it already has.

Please could someone do me a shortlist of what it can be...

Nica_Dom 06-16-2013 05:43 PM

not that i want to highjack a thread but BUMP on the last question

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