View Full Version : Misfire/backfiring

09-16-2007, 08:47 PM
Hey guys my jeeps been running weird for the last couple months, slowly getting worse. It has a random slow starting problem, usually when hot, always starts though. On the highway cruising at like 100/120 km/h at like 2000rpm it misfires and you can feel the truck stuttering a bit, easing on or off the gas makes it stop. This past weekend it started backfiring when that happens, even driving around the city it backfires now. It has lots of power and seems to drive perfectly fine. Fuel milage is even pretty good.

1988 Wagoneer limited (cherokee), 4L.

Here's what I've done recently:

-Air filter
-02 sensor
-Oil pump
-Cap/wires/rotor/plugs (factory champion plugs which all looked fine)
-Fuel pump

Looks fine on the scanner, this year doesn't store codes but it running open loop and all the sensors are within specs including fuel preasure. I really don't know what else it could be...injectors or stretched timing chain is all I can think of but both are expensive tests. Anybody with any idea what it could be please help me!

09-16-2007, 08:49 PM

09-16-2007, 09:12 PM
thats what i was thinking too .

do a compression check or leakdown

09-16-2007, 09:13 PM
shoot it...its a jeep...

09-16-2007, 09:30 PM
Fuel filter...in regards to the stuttering, letting off the gas making it better issue.

09-16-2007, 09:31 PM
could be tps sensor

09-16-2007, 09:32 PM
Fuel filter is new...fuel preasure looks fine. Previous owner said the TPS is new.

I don't see how a headgasket could be the issue of the symptoms I have, but it very well could be, 220,000kms on the jeep and it has been overheated.

How would a headgasket give me these problems?

I can do a compression test and a leakdown.

09-16-2007, 09:34 PM
pressure test the rad if your losing pressure your heep is hooped

my headgasket just went in my blazer did same symptoms but was leakin through exaust area so i was blow white smoke like crazy my guess is that damn gasket

have fun

09-16-2007, 09:37 PM
water gettin in cylinder would cause it
your distrib could be wet to
or i dont know if it has that est could be ign module inside distrib

09-16-2007, 10:04 PM
fuck, okay i'll do a leakdown tommorow.

Don't think im losing any coolant and no white smoke so I got my fingers crossed.

09-16-2007, 11:58 PM
shoot it...its a jeep...

dont you watch horror movies man? Just shooting it never works[16]
Ya gotta pull it all apart and burn all the peices individually then bury the remains as far apart as possible to keep it from ever comin back[cheers]

09-17-2007, 01:02 PM
I just plugged in the scanner it shows that the TPS is only opening to 20%. It doesnt cut of and stop 20% after opening it, it just gradually builds up to 20%, and if I unplug the connector going to the tps from the tranny it reads fine. I guess ill pick up a new TPS and see what happens.

09-17-2007, 01:12 PM
Crank / tdc sensor can also cause hard starting.
Also check to see if the timing chain is stretched.

09-17-2007, 01:58 PM
Are you talking about the crankshaft position sensor? Cause I already did that.

and yea the timing chain seems pretty loose, had a poke at it when I changed the oil pump.

09-17-2007, 02:25 PM
Fuel filter is new...fuel preasure looks fine.

Alrighty. But, Pressure and volume are two different things, just sayin'.

09-17-2007, 03:00 PM
Heed my advice or this haunting will never end

09-17-2007, 05:29 PM
Alrighty. But, Pressure and volume are two different things, just sayin'.

but I should see a pressure drop if it was starving for fuel wouldn't I?

I went and took a TPS out of a wreck and I think it mighta helped. This one reads up to %77, better than 20 I guess. Hasn't backfired since, but I just went for a putt up and down my street though.

09-18-2007, 12:19 AM
just got back from the gym. Still backfiring the same. Leakdown tommorow I guess

09-19-2007, 04:18 PM
Compression was 150, 130, 150, 155, 150, 155. Went up quick, 3 strokes to build up max PSI. Manual says 120-150PSI is fine.

Number 2 spark plug ended up breaking its in an awkward place and I think it was just me taking it off. All the plugs are a few days old and all looked really good and consistant, even number 2.

Maybe the injector on number 2 is fucked, or a worn cam lobe on that cylinder? Anyone have an extra injector I can test with?

09-20-2007, 08:50 AM
Ya 120 to 150 is fine but one cylinder with a drop of nearly 20% isn't very good. Messes up the balance. Not that that's your problem, but it's still not great.

09-20-2007, 10:50 AM
found out a a way to figure out timing chain stretch or to see if it skipped using the distubutor and keeping the timing cover on.

Trying that today

09-20-2007, 02:57 PM
Did all the timing chain stuff tests, doesn't looked like it skipped, (distributor lined up to #1 plug at #1 TDC) and i could barely turn the crank back and forth without the distibutor turning so it's not stretched.

Thinking of taking it into someplace where somebody else can screw with it now.

09-21-2007, 01:32 PM
All the systems for the egr appear to work fine. Egr itself is not working I don't think. If I apply vacuum to the EGR it should move and the engine should die if its running, right? The valve won't hold any vacuum, and won't budge with vacuum. With pliers I can move the shaft back and forth it slides really smoothly but I can't really budge it with my finger.

If the EGR was stuck closed shouldn't everything be running fine anyway though?

90 bucks a new one that might not fix anything is tough as I'm starting to run out of money over here.

09-22-2007, 08:34 PM
drain your tank could be water in fuel

09-23-2007, 12:07 PM
hmm...well egr did nothing

09-29-2007, 11:57 AM
FAWK...just ran combustion chamber cleaner through it and now I have a tapping noise. Changes with load almost completely gone cruising. You can hear it all rpms..not a thunking like bottom end, still got lots of power.

10-10-2007, 11:17 PM
The tapping noise was the just the EGR tube comming loose causing an exhaust leak. Fixed that after my panic attack.

Backfire and misfire are still around though. :dontknow:

10-16-2007, 12:44 AM
Thats a strange one, it seems like you've almost exhausted all your resources of doing it yourself without serious diagnostic. You're sure its a back fire tho? How's your exhaust system? That much backfiring must be wreaking havoc on your cats.

10-16-2007, 07:40 AM
It has to be backfire, can't imagine what else it could be...

10-16-2007, 10:09 AM
Yet its not loosing power when it happens???

Its kind of a long shot, but how are your spark plug wires? are they arcing between each other? Look for signs of burning and wear on the wires then, wait until night fall and have your truck running and borrow your wifes water spray bottle for her hair and just mist the wires, see if the wires arc between each other.

10-16-2007, 06:47 PM
lol wife? That scares me...I'm only 18.

Ummm i'll give it a check in a few minutes it's just getting dark but the wires are new...doubting that.

Yes I do lose quite a but of power when this happens.