Lost top end power in 88 Cherokee 4.0.

Did you open up the old fuel filter, or blow it backwards into a can to inspect for dirt or sparkles that could indicate a pump dying? I would run a fuel pressure test, and then a cat pressure test.

Yes I did blow out the filter and besides being a bit hard to blow through, it appeared ok. Rotted pretty bad though.

I have no cat to check, well there has been nothing 'in' the cat since before I bought it and it still passed emissions great.

I have no real way to check for fuel pressure I don't think unless one of my old compression testers could be converted??

The miss is pretty consistent.

Thanks,

Mike

Plug wires can do this, but they will usually give you some backfiring along with the bogging down.

Earle

Look at simple things, it sounds like it might be starving for fuel? Test fuel pressure and flow, consider clogged catalytic converter, look for a stopped up fuel vent. You changed the fuel filter, is there possibly another one, maybe in the tank?

What does exactly "then just bogs" mean? The Jeep does not go any faster, or it stalls and stops? What precise noises/knocks and symptoms, etc?

On idle, what happens if you press accelerator until above half throttle? Is there a loss of power?

If the fuel pressure is low, the engine can run fine upto a point, until the demand for fuel exceeds the supply due to low pressure.

Stalls and stops and sputters until the gas pedal is let up on.

No backfires.

EGR now unplugged.

If I go fast on the pedal, there is a dead spot. No load and smooth pedal seems to work.

I knew there was a reason that filter was the second thing I went after. ;-) I don't have a pressure gauge other than a compression gauge though.

I also have verified the coil wire still has a connection with the ohm meter. It is a bit higher per foot in resistance than the plug wires, but only a bit, .7K vs .5K. Hmm the others I have around seem the same too....

I made sure the main power had good connections also.

Mike

I would use a guage capable of 100PSI, but your local parts store may rent them. A "miss" and "bogging down" are two different things. If it is a miss, I would change plug wires just to eliminate that possibility, then if not effective, follow the fuel pressure.

Run it hard and make it bog and them pull over and remove a plug and see if it is white or sooty. I tend to think you are getting a fuel starvation here that surfaces at higher power settings. Hard to be sure without feeling it but the plugs would confirm a lean out. Might start by changing fuel filter like someone else suggested and maybe a fuel pressure check too.

----------------- TheSnoMan.com

Don't disagree with you at all but the OP says he already replaced the fuel filter, my question: Is there another filter somewhere?

I had a Cherokee years back but I no longer have the service manuals so I don't know if there is another filter.

What about the fuel vent? That's easy to check by driving with the gas cap removed.

I've had this situation twice. First time was a dying fuel pump - and it progressed to dead pretty quickly. Second was a shorted cable to the CPS. Didn't tie it back properly and the exhaust got it. Same symptoms, except my max RPM was 1000-1200 RPM, period. Crept home at idle .

Mike, it really sounds like a fuel delivery problem. Because you changed the fuel filter, I would suspect the fuel line is pinched or you have had a piece of rubber fuel line come loose and restrict the flow. It also could be a fuel pump on the way out.

The other obvious thing would be a collapsed baffle in your muffler restricting exhaust flow. I've had that happen to me.

Either the fuel is not getting in or the exhaust is not getting out. I wouldn't suspect ignition because it doesn't miss or backfire.

Merrill

Water in your float bowl. God Bless America, Bill O|||||||O mailto: snipped-for-privacy@aol.com

Since you are just fishing... check the ignition coil input/output coil voltages and the capacitor. Verify spark can jump a large gap when engine is not running. Check this article:

I would still check the fuel pressure and the fuel presssure regulator.

Yes Bill

I agree that it sounds like water in the float bowl, but I thought the Canadian 88 4.0 was FI. Don't hesitate to tell me I am wrong.

Merrill

And you are wrong.

Again.

Fuel vent is viable too but more so with a fuller tank when there is less air to expand as volume in tank increase. . If filter has been changed then fuel pressure shuold be checked too and if you had a gage with a long hose on it to could drive vehcile to failure mode and check pressure while doing it and if pressure stays good than fuel system can be ruled out but if it dropped then you have your culprit. Also I am not sure if the is a screen or sock filter in tank on fuel pickup on that model Jeep in regards to a second filter.

----------------- TheSnoMan.com

There is a sock filter on the pump in the tank.

What would I explode if I try blowing back through the line from the tank side of the inline filter.

The tank is new since we bought the Jeep, but...

I will go try some more up top electrical things first now.

Mike