PapaBearXJ88

1988 Cherokee 4.0 Renix, all stock.

Ready to put this thing down if I didnt love her so much

After engine overhauled and reinstalled it idles “OK”, but will not accelerate at all (idles 600-700, but when throttle is applied stammers like there is a possum in the crankcase - no power, will barely go past 1100 rpms (and that's pushing it). Sounds like it's missing maybe? Sounds like a timing issue, but there is no indication as to anything that would cause timing issue (and it is showing ignition advance of 15-16 degrees at idle, but could surge up to 30 degrees, while still at a high idle.

Here's what's been done:
Engine removed, overhauled and reinstalled. Cylinders polished (not bored, minimal ridging, so honing was all it needed). Pistons reused, new ring set installed, valve job performed, head shaved/resurfaced, new camshaft and new lifters installed. New timing chain and gears installed. Crank shaft polished and reused. New oil pump installed. New main, cam and rod bearings. New gaskets and seals. New exhaust manifold and doughtnut. All components cleaned and reassembled (including fuel injectors, throttle body, intake manifold, EGR valve assembly, fuel rail, all others). New flexplate installed to replaced cracked one.

New TPS, new Crank Position Sensor, new O2 sensor, new distributor cap, plugs and wires, rotor previously replaced and in good .

Tested all sensors while installed, all within limits. Retested using NickInTime Designs REM II Renix Engine Monitor (Thanks Nick, awesome resource to have!), all sensors again show within limits. Just before engine died out after idling for a while, exhaust shows LEAN, O2 locks in at 4.92v (which is odd since ECU considers <2.5v from O2 sensor to be RICH?).
Short Term Fuel Trim maxes out at 255, Fuel Injector Pulse Width a little high - 11 milliseconds at idle, seems like it's starving for fuel, but again, plugs were black?)

Indexed distributor twice (from TDC#1). Removed cleaned and reinstalled plugs (had turned black fron running for approximately an hour or so).

Gas has been in tank since I started in August 2017 (about 6 months). Bad gas maybe? Checked and double checked all vacuum lines, all look good.

Did Cruiser54's tips on connector refreshing (including C101) and refreshed and beefed-up grounding (replaced braided ground wire from firewall with battery cable and eyelet, removed, stripped and replaced ring connectors on oil dipstick grounds, sanded all paint off of all sides of dipstick ground, then added ground jump wire with 12 gauge wire directly from negative battery cable connection on block to oil dipstick ground. )
Hopefully grounding should be solid.

HEEELLLP! I've spent enough man-hours on this beast that if I could pay myself, I could buy a new Jeep cash money! So close - but so far away. I'm at the end of my rope. Any help would be greatly appreciated.

cruiser54

Check your distributor indexing:

http://cruiser54.com/?p=68

Bugout4x4

It also sounds like it could be a timing chain issue. It could have been installed one tooth off. I've done it myself a few times, and they will still run but this is exactly how they act if everything else is good.

PapaBearXJ88

Thanks Cruiser and Bugout, I'll re-index with your instructions and kee the timing chain/gear in mind if I can't fix it otherwise. I was also told that sometimes new aftermarket flex plate can have the timing marks can be off. My old one was cracked, replaced with one from Advance Auto. I'm saving the mechanical things for last hoping it's electrical. Fingers crossed.

Here is a link to a video of what it is doing and the sensor readings.

PapaBearXJ88

I read the Distributor indexing link and I have a coulpe of questions:

1) I did as it said in the instructions previously, if by chance I indexed it when #1 was on exhaust stroke instead of compression, would it still run and could that be the problem I'm having?

2) Since I don't kmow if it is in the right place, I should just go by indexing with TDC as determined in Tip 12, and not worry about trying to line it back up by cutting the window in my cap, right?

PapaBearXJ88

I lined-up the harmonic balancer timing mark with the 0 on the timing chain cover. Pulled the dist cap, rotor was 180 out (pointing at #6 instead of #1). I pulled the distributor, turned it to point at #1, now it will not start at all.

I ran out of daylight before I was able to properly index using the instructions Cruiser54 sent, but plan to do so in the morning. I went ahead and pulled the plug from #1 and since it was out I probed the cylinder with my cam probe to see what was going on and the pictures in tis post show what I saw (these are of the top of the piston on #1) What could cause this? Have I messed-up my new engine!?

I'm beginning to wonder if maybe the shop misaligned my timing gears like BugOut4x4 mentioned? How else would harmonic balancer mark not line u?

cruiser54

In my write-up on indexing, there is a link to another write-up on guaranteeing you're on #1 TDC.

Bugout4x4

These are pretty blurry, but is that extra metal in there that should not be there? Is that metal around the valve and seat there?

PapaBearXJ88

I think that is the raised edge of the piston, I dont hear anything rattling around in there, I'll look closer in a minute while I'm putting it to TDC.

I was wondering about all of the burnt spots on top of the piston, any idea what would have caused that? I've been having problems with the timing, do you think those are detonations from where it was off-time? Does this cause me any problems or anything to be concerned about??

Bugout4x4

Oh yes, it could definitely be burnt spots. But if you get back in there again take a good look around the piston head above the ring groves. It was hard to tell but it looked like maybe some of it was missing on one side there. But it might have just been the lighting. Hoping I am wrong...

PapaBearXJ88

I re-indexed according to the link that you sent, - absolutely positive it was at TDC on #1, still will not run right, even worse now (will barely fire up then shuts down).

My wife covered the spark plug hole with her finger and let me know when it was being pushed off by the compression as I turned by hand. She then put a screwdriver in and let me know when it got as high as it would go, then when it started to go back down. I back it off slightly so that it stopped between those two points. Pulled distributor, put oil pump slot at 11:00 and the rotor at a solid 4:00. Lowered right into position ending at 5:00, pointed at #1 plug wire.

QUESTION - is there any way that the shop could have put the timing chain gears are on wrong, or mis-aligned the cam shaft? the balancer shows TDC to be at the the fifth mark from the bottom on timing chain cover (6-degrees BTDC accordding to the diagram I'm looking at?)

This may sound like weird questions, not sure, but we're in uncharted territory, beyond my level of skill, I just know something is not right, and I've pretty much eliminated everything electronic I think, so I'm wondering if it could be mechanical?

Bugout4x4

It's not weird at all and very possible they installed the timing set wrong. Honestly, it is easy to do on these, I had to reset and recheck mine twice before I got it right and I know what I'm doing.

"Just line up the marks with each other" Well that is not the case, they don't quite point at each other even when installed right.

If your damper is off from dead center when the piston is smack dab at the top then this could be the issue. It could be off a tooth on the chain. And like I say they will run but terrible.

Bugout4x4

One other thing to try though before you get too excited. If you think it could be bad fuel, and you now know you have it indexed correctly, You could try pouring just a "little" fresh fuel down in the intake and see if it cleans out and runs correctly while it is burning that fresh fuel.

PapaBearXJ88

Drained the remaining old fuel today and replaced the fuel filter, tried a little fresh fuel in the throttle body, but as soon as It cranked I noticed fuel filter hose pouring like a river. Seemed to crank a like easier, but could just be wishful thinking, I plan to get on it in the morning. Take a look at the attached pic - The fuel MAY not be THE problem, but this was definatly A problem!

The whtie at the bottom is the water that had separated from the old gas. Ugly.

I found this other thread where a guy had very simlar issues and tried a very similar route that I have been: https://www.cherokeeforum.com/f2/94-...g-issue-91667/

He finally fixed it by setting the distri one tooth forward I think? THoughts?

5-Speed

Hey, uhh, thats not gas anymore. Dont mess with the timing until you are sure all of, whatever that is, is gone.