Jeep makes "popping" noise under load

[kyleag89]

Well more problems with the MJ today. It ran fine all day then out of nowhere it lost power and would make a popping noise from the motor area when I would press the gas pedal more than half way. Then it started running ok and when I got on the highway any faster than 65mph it would loose power and pop again. Any ideas?

[Dave Stark]

We're going to need a bit more info: Year, Engine, Transmission, 2 or 4wd. Did you do any recent work to it? Anything that may be pertinent.

 

:wavey:

[one_bad_MJ]

timing. bad gas we need more info

[kyleag89]

Its an 89 renix 6, 4wd with 160k. I haven't done anything to the motor other than test all my sensors to make sure they work properly. I am thinking fuel issue or maybe manifold leak? If I buy a fuel pressure guage and test that how would I know exactly what to replace? I mean it could be the pump, injectors, or the pressure reg. The fuel filter is new.

 

Also how would I test to see if the timing chain is ok? Would I just put the light on it and see if the timing is at "x" degrees, whatever it should be?

[Geonovast]

I'm betting the timing is fine. If the chain had jumped a tooth, it would run crappy all the time.

 

Sounds like a fuel issue. Get your fuel pressure tester, at the rail running should be about 40 psi.

[kyleag89]

Ok so if it isn't 40psi what would you suggest replacing first? The pump or could it be the fuel pressure reg? I'd hate to drop the tank and have it be under the hood.

[Geonovast]

If you have another regulator sitting around, I would try that first. The most likely culprit is your fuel pump though, if you've recently changed the filter.

 

It could also be your O2 sensor dying. If that's malfunctioning, the ECU may be dumping too much fuel, causing it to backfire.

[88pioneer]

An if your truck has one check the ballast resistor

[kyleag89]

Thanks guys.. I will check the fuel pressure first and go from there. The o2 sensor also sounds like it might have something to do with it.

[Wildman]

Seeing how your some what new here, and didn't check out the total forum......

 

Here's the step by step testing of the fuel pump, make sure you use the MPI steps -

 

http://www.lunghd.com/Tech_Articles/Fue ... ostics.htm

 

 

When you say you have a "Popping" noise, do you mean a 'mis-fire'??

 

It could also be your CPS that causing a mis-fire.

 

And also the O2 sensor.

 

Here the complete Renix sensor testing schedule -

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

 

Your '89 will have the ballast resistor.

 

There is no timing to set on the 4.0, the timing, and injector pulse is controlled by the ECU.

 

If the chain was stretched, which seldom happens on the 4.0, like Geonovast stated, the truck would be running like crap all the time.

 

Also, with the mileage you have, check the EGR valve, and check for Vacuum leaks.

 

And.......here's the check for vacuum leaks -http://www.lunghd.com/Tech_Articles/Engine/Vacuum_Leak_Diagnostics.htm

[88pioneer]

Vacuum is a good possibility also, my line into my map sensor was snapped clean in 2 an it made it start crappy, and idle high

[HOrnbrod]

I'm not even try this until we hear what/where/how it sounds/where it's coming from "popping noise" is. Sounds fuel related though.............

[one_bad_MJ]

a POP noise is backfire through the intake manifold. check your plug wires and plugs just to be safe.

 

 

and check to see if your dizzy moves around at all. if so it could be retarded and make it backfire or miss.

 

and check your plugs too if there black from loading up it could be a cyl misfire.

[HOrnbrod]

a POP noise is backfire through the intake manifold. check your plug wires and plugs just to be safe.

 

Thank you for that enlightment. :brows: I was not asking you, I'd like to hear it from the OP.

[Eagle]

Ok so if it isn't 40psi what would you suggest replacing first? The pump or could it be the fuel pressure reg? I'd hate to drop the tank and have it be under the hood.

Is it or isn't it 40 psi? If you don't know the pump might be the problem, why ask how to replace it? In any event, you don't drop the tank to replace the fuel pump, uou just drop the drive shaft. (Good excuse to replace the old u-joints)

 

The popping could also be caused by a bad oxygen sensor. If it isn't responding to changes in load and mixture quick enough, it can result in more fuel being injected than the engine needs. The unburned fuel goes right through, and then ignites when it hits the catalytic converter. This results in a muffled series of backfires that might be described as "popping."

[kyleag89]

Thanks guys but I have been a member for about a year and I already know of the "lung" write ups and I have used it to check all my sensors, the plugs, wires, and dizzy are all new.. I replaced the ballast resistor last week and the IAC. I haven't been able to buy a fuel pressure tester yet so I have no idea what kind of pressure there is. I read the write up on testing the MPI injection system and I will do that ASAP hopefully in the next few days when I have time.

 

I am almost 99% positive it is the fuel pump after hearing what you guys said, but I won't know for sure until I get the tester on it. I drove it today for the first time in awhile and the pump was whining louder than usual so I'm sure that will be the culprit. I will replace the O2 sensor to since the one thats in there is questionable. So I have it narrowed down to fuel issue because EVERYTHING else is either new or been inspected and checked out in working order.

 

Thanks I will keep you posted when I do the test..

[kyleag89]

I forgot to add that all the vaccum lines are also new, and the egr works fine. The exhaust is new from header back with no cat.

[Wildman]

If you have a Harbor Fright near you, they have a fuel pressure tester for about $20, it's not the best, but it works........until it starts leaking out of the gauge :roll:

 

Not sure if Advance / Auto Zone loans them out :hmm: you could check

 

One question, after your last post..........how old is the gas that your running now???

 

If your fuel pump is whining very loud, that's a sign that's it about to crap out.

[kyleag89]

Gas is only 3 days old..

 

I got a fuel pressure tester tonight and started troubleshooting. The pressure was 39psi w/vac unhooked and 30psi when everything hooked up as normal. Although the pump is screaming at me and sounds louder than it should be it passed the flow test. I didn't get to do the leak down test yet because it got dark. Anyone think the injectors are possibly very dirty? I guess I will clean them tomorrow.

[kyleag89]

I'm so stumped I just went out with Mr maglight and pulled the two easy plugs and they were both white as a ghost... The dizzy still looks new inside. Too lean and it doesn't run too hot.

[jimoshel]

Not sure how FI would be different from carb but I had that problem with a carburated engine. It was a sticking intake valve. A little Marvel Mystery Oil down the valve stem cleared it up. A compression test would show it up.

[kyleag89]

Ok so I guess I will run some MMO through the vac line and put some in the gas and hope that will clear up any issues that the motor and fuel system may have. I prefer the MMO over the seafoam too Eagle.. lol I have seen MMO do things seafoam could never do!

[HOrnbrod]

Ok so I guess I will run some MMO through the vac line

 

Wha?

[kyleag89]

Marvel Mystery Oil..

[kyleag89]

Thought I would update this post for someone who may have this problem in the future.

 

I ran some Seafoam through one of the vaccum lines on the intake manifold and put some in gas tank. I also added a little Marvel Mystery Oil into the engine oil. I then removed and cleaned my injectors and put new O-ring seals on them and it runs perfect.