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Miss, stumbles, jerky at decel.

J

Jasper911

NAXJA Forum User
Location
Louisville, KY.
Newby here looking for some direction.

Having an annoying stumble off idle and jerkiness when letting off the gas...Having to compensate with clutch and would really prefer to not have to do this. Always seem to have to put more foot into the pedal than should be necessary at cruising speeds. I also notice a sag under hard acceleration and the idle could be smoother too...slight miss can be heard at tailpipe. Just replaced the wires, cap, rotor and plugs (oe type Champions...not my choice but what they had that day) as well as air and fuel filters. Made no performance difference, however the plugs were pretty worn and the wires could shock at touch.

I tested the TPS with a volt meter and could not get a good numbers that seemed to correspond with the specs so I replaced it to no benefit. I was kinda hurried, might've had the voltmeter hooked up backwards or something.



'96 4.0 5 Speed 102,000 miles ex Forest Service.

Thanks and happy holidays.

Justin
 
It was probably a couple of mms. side to side. Enough to let the rotor contact the cap.

Still have an annoying jerkiness at around 1000rpms, mostly noticeable at deceleration and enough to make shifting less smooth and easy. Something is still just not right. Need to check the tb base gasket for air leaks and the temp and map sensors too.
 
Rode around with the scanner hooked up. Only got a pending code for a #2 misfire. No other codes. Replaced new Champions with new NGKs. No difference, but I wasn't counting on any.
Like the accelerator is hair triggered either way...push down/let up. Not a smooth transition. And the spot where my foot would be gently relaxed on it for cruising isn't available.

Oh, checked the cat. and it was fine inside, nothing loose or melted over the honeycomb. And did the compression. Completely even on all cylinders at around 120psi. with the fuel pump disabled. Don't know if that actually changes the readings or not.

I always thought 96 and up was OBDII, but I was led to believe differently by the Haynes manual implying that 97 was the first year for it. I was right originally and made to look like a dummy in front of my cocky ass brother.
 
Possibly bad injector. Try swapping it out for one from the third cylinder and seeing if the missfire changes to #3.
 
I just had the injectors out and at an injection service shop where they were tested and all checked out okay.

I have seen where some injector harnesses had funky wiring, but I figured I would get a code for an injector malfunction.
 
I've had the same problem, most likely IAC or TPS. Pull your TB and clean out the passages real well. If this symptom occured only after DIST. install, re-check your distributor Cap+rotor.
 
I actually replaced the TPS to no result. Had the problem before the distributor install.

The plug wires are less than a month old and are good quality.

962, did you have any codes showing with your problems?

ALso, if I remove the IAC, can I get a replacement gasket for it?

Was kinda bummed, checked my harness today. It doesn't even come near the rear of the head or valve cover, so interference damage is not likely.

Also, took a propane torch and tried finding vacuum leaks on or around the intake etc.
 
No codes when I had the IAC issue. As far as the gasket, if the old one is undamaged reuse it. If you have to get a new one, I can;t recall if the IAC came with it or not?
 
No, it's the motor. Eventually, if unaddressed, it will be a driveline destruction problem as well. There is a miss/crossfire very evident at the tailpipe at idle and a visual "shiver" by the engine. There is a jerk at approximately 1000rpm when decelerating. Makes a smooth downshift impossible. I tried a new map sensor, iac valve and coil and nothing changed. It almost acts like a head gasket crossfire. I would hate to pull the head and do all of that only to have it go back together and still be the same. Compression is about as even as I've ever seen, the old plugs all looked the same, engine temp was 197 on the scanner.
 
I've done a lot of jiggling of the underhood wiring harnesses and can't cause any changes either. I have also pulled, checked and reconnected just about all of the underhood connectors but none have been nasty in any way.

I read a post that someone had a fuel pump not producing full pressure with some similar issues. I'm gonna check the fuel pressure in the next few days or so.

I did notice that my coolant overflow level has not changed in the 3000 miles or so I've driven.
 
Get your hands on a FSM for your year and read up on the "modes of operation" section in the "Fuel System" section.

On the Renix system the ECU does some interesting things in deceleration--including cutting off the injector pulse under the right conditions.
 
Checked the fuel pressure today and it's at a nice steady 50 psi. Listening to the tailpipe putters, I'm pretty convinced it's the head gasket allowing cross-firing. Been here, done it before with prior vehicles. Always hold out in denial though.
 
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