89 XJ will not accelerate after rebuild

Hey y'all,
Last year I rebuilt the 4.0 on my '89, but after screwing around with it I got frustrated and left it sit for the last few months. Here's the deal>

The engine starts great. Seems to idle great. Idles around 5-600ish rpm. When I give it gas and the rpms get over about 900ish, the motor starts to sputter and bog down. I've replaced the CPS, all the vacuum lines are new. I've checked and rechecked the distributor, I don't *think* I'm off a tooth. What else can I check?

Edit: The jeep will not accelerate at all, if I keep on the gas it just bogs down, sputtering and backfiring. The engine doesn't actually die, however.

Thanks,

Tony

got to be the distributor indexing.

its probably one tooth off correct timing.

Have you tested you MAP (Manifold Absolute Pressure) sensor? If they go tits up, they can produce your symptoms...

Also, make sure your TPS (Throttle Position Sensor) is adjusted correctly....

check fuel pressure for shits and giggles. i just got done putting the motor in mine and low and behold, my curse strikes again, fuel pump low output.

X2 on the TPS... If adjusting it does not work, Go get a new one, and if it does not fix it, you can take it back the same day...

92DripCherokee said:

got to be the distributor indexing.

its probably one tooth off correct timing.

Click to expand...

Triple check this... Also, double check firing order of the plugs. Stupid, I know, but i've done it times that I swore got them right, and I hadn't

OK,
last night I checked the following:

TPS: closed .2, open 4.0, reference 4.5V.

Fuel pressure; 29lbs at idle.

Distributor: Re-indexed twice, couldn't seem to match a picture found here. Got frustrated and ground off tab. Now matches picture exactly, still have the same problem. Grrr...

How can I check the MAP?

What do you adjust on the TPS?

I'll doublecheck the firing order, but it idles perfectly, so I doubt that's the problem.

The only other think I can think of is bad fuel. I can't get a hose down the fill neck to siphon it and I'm not real excited about laying under the tank while I disconnect hoses to drain it from below. I've got 3/4th of a tank, and it's old gas. Any better ideas on siphoning?

Thanks,
Tony

Does it have enough "good" gas in it? That petro will go bad sitting in the tank.

This may sound silly, but on the TPS, make sure the throttle is actually pushing the lever on the sensor down. I've seen guys in a rush not get the lever under the throttle link, so it was not working at all on the throttle side and the truck ran like poo. you can loosen the screws and rotate it to adjust. With a volt meter, measure the volts at the 4 prong connector that has only 3 wires in it. You want 5 volts from A and D , and 4.2 volts from B and D with the engine off and key on. If you cant get somewhere close to 5 volts on the first, check grounds. (mine was only 4.8 and most are lower than 5) If you can't get close to 4.2 on the second, you need a new TPS

OK,
All the gas in the tank is *ahem* aged. Is there something I can add to the tank to help it out or am I stuck with getting gas all over me, the driveway and into the nearby river while trying to drain it from below? The problem here is we're talking about 12 gallons or so (it's a 15 or 17 gallon tank, isn't it?) so I don't think just adding new gas to it would make a lot difference.

I'll check the TPS again, as I recall, there's actually two connectors on it...one is a boxy affair with I think 6 wires and one is a flat one with 3 wires. I was testing on the flat one with 3 wires. I don't know what the other one's for, I just plugged it into what I unplugged it from originally. This is a fuel injected motor.
I do get a changing voltage when testing, so I'm pretty sure the lever's connected.

Wilfite said:

OK,
All the gas in the tank is *ahem* aged. Is there something I can add to the tank to help it out or am I stuck with getting gas all over me, the driveway and into the nearby river while trying to drain it from below? The problem here is we're talking about 12 gallons or so (it's a 15 or 17 gallon tank, isn't it?) so I don't think just adding new gas to it would make a lot difference.

I'll check the TPS again, as I recall, there's actually two connectors on it...one is a boxy affair with I think 6 wires and one is a flat one with 3 wires. I was testing on the flat one with 3 wires. I don't know what the other one's for, I just plugged it into what I unplugged it from originally. This is a fuel injected motor.
I do get a changing voltage when testing, so I'm pretty sure the lever's connected.

Click to expand...

It's a 20 gallon tank, and the boxy connector is 4, with three wires in it. that's the one you want to test exactly how stated above. the connections are labeled on the plastic part, A, B, C, and D

I have let vehicles set for YEARS, and never had problems with the old gas. I doubt that is your problem.

The TPS voltage on the flat connector 3 wire set should 0.83 V at idle, not 0.20. You have a bad TPS or calibration or mounting problem.

Make sure the MAP sensor has an air tight vacuum connection to the intake manifold.

Check the grounds, rear engine head to firewall, and engine block near the oil dipstick / oil filter assy to the battery negative post. If you fix a poor ground you need to RE-calibrate the TPS.

How about the exhaust, is the exhaust clogged up?????? Busted Cat, busted baffle plate in exhaust, or a varmit :shiver: crawled up the tail pipe while you rebuilt the engine.

Tell us about the plugs and wires, cap and rotor...

The fuel pressure with engine running should be 31 psi, not 29. If you disconnect the vacuum line from the Fuel Pressure Regulator (FPR) the fuel pressure should be 39 psi. FPR could be bad, or the fuel filter cloged.

Alrighty,
Got a new TPS, calibrated, no change. I don't think there was anything wrong with the old one, really. Reference voltage is still 4.6V. No cat in the system, 2.5' exhaust. It would take a lot of critter to block it, i would think. I haven't seen anything up there. I'll take another look at the fuel pressure.
The cap, wires, plugs & rotor are all new.

Thanks,
Tony

To me it still seems like a timing issue. are you 1000% sure that your chain is not off a tooth? a tooth off would still allow the idle to be fine but would do exactly what you are saying. Try to retard the timing a bit. My experience with drag cars has been that when it is too advanced it will fall flat on its face and backfire and pop etc. kinda what you seem to be experiencing. This is my opinion based on years of building and racing VW, Porsche, Audi and MG's. This is not based on anything with a jeep but when i have had engines fall on their faces and pop it was almost always a timing related issue.

I am sure that someone here knows alot better then I do, but if your chain timing is off then your CPS would be off time, Your cam would be off your injection etc. At the very least turn the engine to TDC at the number 1 piston not the distributer and find out where your distributor is pointing. I know it is not 180 off or it wouldnt have anything but popping but i bet it is off some.

Hope this helps. If not, Sorry to have wasted your time but it would be the first thing i would be checking under the same circumstances.

Bug

anything new with this?

Sean

Hey guys,
I was out of town for a week. With a sinking feeling, I'm beginning to think it's the tooth off on the chain. I probably won't be able to do more than tinker with it for a few weeks due to other responsibilities. As i recall from when I did the rebuild, the book procedure had me counting teeth from the dot to where the chain and sprocket meet, something like 15 teeth, i think. My question is, does this mean the tooth that's actually solidly in the chain or the one that's just about to enter the link? Is there a better way to line these things up?

Thanks again,
Tony

if you line the dots up on the gears it should be fine. the distributor may be 180* out but you can take it out and re index it

OK,
It's been a busy several weeks but I finally got some work done on the Jeep last night. I'm 99.9995% certain the dizzy indexing is fine. I pulled off and re-installed the timing chain, dots match up perfectly. It's still doing the same thing, idles fine but when given gas it sputters and bogs down.

I have a couple of thoughts:
1) Will a bad stator do this? I had two dizzy's and found (quite by accident) that the one I installed had broken off the hall effect sensor on the stator. I put the other one in (it's all there) but no change. How can I test this sensor?

2) How do I test the MAP?

3) It just occurred to me that the block I rebuilt and put in was out of an older model XJ. I don't remember, it might have been an '84 or an '87. The crank and cam were sent out by the machine shop to be reman'd. With that in mind, do I need to do anything different with regards to timing setup? I'm aware of the TSB about advancing the rotor .020, and while I haven't cut a hole in a cap to check it, it looks like it's there.

Any other ideas? So far I've replaced the CPS, TPS, vacuum lines are all new, no loose connections in vacuum or ground that I can find. Fuel pressure ok. Timing chain re-installed, dots line up exactly (not sure if it really was out or not in the first place). I've tried putting the dizzy out a tooth either way and it either runs worse or won't run at all then.


I'm perplexed. This thing has gotta get running soon, I need the 4wd for winter and my pickup needs a rest.


Thanks for your help, folks.
Tony

go here for testing the sensors http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

the stator or sometime called camshaft position sensor could be bad. my understanding is that it controls when the injectors fire.

I'll have to agree with the timing. I had a Ford 3.0 go about ten degrees off in its timing. did exactly what you're describing. No power. By the time I figured out the problem I had cracked the block in six places. What a pain that was.