HELP 98 GRAND CHEROKEE ROUGH RUNNING

Sounds like you still have an injector problem. Try hooking up a noid light to each one while the engine is cold. If that passes muster, they may all have to be pulled for further testing and cleaning.

What sort of 'crap' are we talking about here? Corrosion maybe? What type/brand of fuel were you running? Ethanol content?

Just reg gas from Canadian Tire no ethenol., but they have been flushed twice, what is a noid light and what is the test procedure Thanks for the reply JD.

Was the maintenance done because of the miss? If not how much was before and after?

Mike

That crap in the fuel rail had to come from somewhere so until you find the source anything else is wasted effort. If the rail was full of crud, think what the fuel filter must look like. And anything that extreme would likely even plug the sock filter on the pump intake

Sure you d> Just reg gas from Canadian Tire no ethenol., but they have been flushed > twice,

Mike it has all been done since the problem occurred. Like I said the fuel tank has been cleaned. the fuel pump and filter replaced, injector flush, decarb the valves and all those components replaced and nothing has fixed the problem, nothing showing on the read outs from all test boxes, and it only when cold' so can't be hoodlum's

So something is up with the cold start circuit. Hmm....

Ok, maybe two problems? Your first issue was with crap in the gas. Maybe you caused the second issue? Just a wild assed guess, but there are a bad run of distributor caps and rotors out on the market for the

Someone voiced the opinion the parts were made in two different factories or countries and they don't mate up together properly.

Cold start misses can also be a bad or leaky plug wire. Even one just not pushed on tight. New ones can be bad too. I check them by spray misting them with water when it's dark out.

Mike

jeepr wrote:

If it is a fuel injector problem, you and your mechanic may end up having to pull every one of them for further cleaning and testing. Cold starts require a lot of fuel to pass through them, and if one is partially clogged, the engine will run pretty rough.

-JD

JD Adams did pass the time by typing:

For injectors, the easiest approach is to yank them and take them to a local shop that specializes in injector cleaning and testing. (usually listed under diesel engine repair)

I've had mine cleaned and tested. It cost far less than replacing one and verified that electrical and flow characteristics were within spec. You can actually see them test the spray pattern and volume.

Almost made me think about building my own tester cleaner. Didn't look that terribly complicated. Mostly just plastic plumbing, a pump, and control circuit to fire the injector for a given time or cycle it while cleaning.

Here is a link that shows some of the equipment they use.

Mike the motor has 124k km on it. When I took off the cap and rotor to replace them as the first step, the rotor was pretty much eroded and the cap contacts and been pretty much wore down so I got a crappy tire set along with the wires and threw them in. The gas issue I'm guessing came from using shell gas about 4-5 years back when they had the defective additive in it. I remember reading about a class action suit for people getting their tanks cleaned. I've been asking around and these are some suggestion from other people, could you comment on their possibilities;

1. cam lobe flat spot
2. timing off, check marks on gears
3. leaky injector

Thanks for your reply. I pretty much have alot or respect for your opinions.

It would be worth opening up the distributor cap and using a bright light to see if it has tracked or arced already. CT did have those defective sets in stock here in the Toronto area anyway. They were informed about them, but no one there gives a crap.

The 4.0 engine is pretty solid. It has a chain for timing that doesn't jump easy. Cam's don't grow new lobes when warm... ;-)

If it is goop plugging up an injector, the stuff might get real soft when the engine warms up. You might need to do another clean on them. Sometimes goop is 'very' hard to get all out of the lines.

It might be worth checking the plugs now to see if any look 'odd'. I would run it for a little while it's it's rough, then shut it down while still rough to see if one plug has a different burn mark on it.

Mine is running rough when damp and on choke right now and I checked the plugs after moving it around in the driveway and found #2 and #5 to be sooty. I am going to take my multimeter to those wires and compare the resistance on them to #1. It should be the same per foot for all the wires. My cap was clean, I checked that.

I have seen bad wires right out of the box as well. I have seen them missing the crimp on the center core. The spark will still jump, but it will miss when cold. This will show up on a plug visually usually.

I really think it will be crud still in an injector though.... Does the

Mike

jeepr wrote:

Mike Romain did pass the time by typing:

Or look to see if it's like mine was when the bushing was gone and oil was coming up the shaft. That causes all sorts of carbon arcing.

Tell me about it. In my old Chevy it took an air compressor and several runs with solvent to get the fuel lines clean. Too bad there isn't an easy way to install a second filter just before the rail.

on the non direct-fire 4.0, 2 and 5 have the shortest cables and when the coil is going you will probably see 1,6 then 4,5 with more carbon/ unburned fuel buildup. (that's what mine looked like at least) Sorta makes sense as the longer wires will take some energy away and with a marginal coil they might not get a full spark as soon as they should. cyl 1 and 6 run the coolest on that engine. If it was 5 and 6 I'd suspect the vac source was sucking in oil. You can't get an oil feed to 1, 2, or 3 from the intake rail vac sources.

Tell me about it. I've had the dang things fall apart in my hands before. Currently I use Bosch and they have held up well to abuse.

Nope. It's got a cold start mode, but that just bypasses things like the O2 sensor.

One thing to try is to start the engine then disconnect the IAC connector. If the engine smooths out then your looking at a sensor problem or a dirty IAC. (Idle Air Controller) For sensors, that can be the MAP sensor (expensive doodad) or (camshaft position sensor in the distributor)

If you think the fuel rail and injectors may be dirty you can go to a shop that services Diesel truck injectors and they will have ultrasonic tanks large enough to drop the fuel rail into while they clean and service your injectors.