YJ 4.0 turns over but won't crank
- Thread starter JMT
- Start date
OP
That is a pretty dirty intake, and you said the old plugs looked bad? Did this thing run like shit when they parked it? Cause If it was mine I would try a top end clean and some mild rev tuning. Yes, redneck but if its all gummed up from running like shit it will clear it out.
Check for vacuum leaks, Check the fuel pressure, if you have a pressure gauge available.
As far as top end cleaner, I would use sea foam.
Check for vacuum leaks, Check the fuel pressure, if you have a pressure gauge available.
As far as top end cleaner, I would use sea foam.
Oh and how old is the gasoline that's in it. I have seen vehicles like this before that have been sitting around for months and the gas is separated.
OP
Yeah, this thing ran like s**t. It’s still running like s**t. It runs smooth if I’m just coasting, but if I give it any gas it’s rough. And this was before and after cleaning the IAC and the throttlebody. It’s just crap, but it is running.
i’ve never done any of this stuff, so we’ll see, I guess I just spray sea foam over the top of the engine and rinsing it off or something like that? I don’t know what Rev tuning is, but I’ll look it up.
OP
OK, I figured out the seafoam. I’ll go fill up and get that done. I think I’ll pick up some beer 
while I’m there
while I’m there
Don't spray seafoam on the literal top of the engine. "Top Engine" cleaner means cleaning the intake manifold and upper cylinders. Seafoam is something you either add to the gas tank or suck through a vacuum hose into the intake manifold.
Try reving the be-jeezus out of it, see if it clears out. A lot of times, a heat cycle is enough to clear the cobwebs of an engine that's been sitting. Fresh gasoline helps too.
ITiming...gotta get a light and check timing. That distributor might be twisted (i.e. twisted in its mount so that the spark signal is out of sync with the crank) . Timing too advanced or retarded will definitely make it run like poo-poo. You can probably rent a timing light from Autozone. Hook the alligator clip leads up to the battery, the plug clamp to plug one wire and aim the light at the harmonic damper pulley. There should be timing marks on the water pump (driver's side) and as the plug fires, it triggers the light to flash, creating a strobe effect so you can see where the spark is timed to the crank. I don't know what the static timing should be for a 4.0L but google can tell you. You twist the distributor in its mount to adjust.
I don't know how far you want to get into this, but a compression check is probably in order too.
ITiming...gotta get a light and check timing. That distributor might be twisted (i.e. twisted in its mount so that the spark signal is out of sync with the crank) . Timing too advanced or retarded will definitely make it run like poo-poo. You can probably rent a timing light from Autozone. Hook the alligator clip leads up to the battery, the plug clamp to plug one wire and aim the light at the harmonic damper pulley. There should be timing marks on the water pump (driver's side) and as the plug fires, it triggers the light to flash, creating a strobe effect so you can see where the spark is timed to the crank. I don't know what the static timing should be for a 4.0L but google can tell you. You twist the distributor in its mount to adjust.
I don't know how far you want to get into this, but a compression check is probably in order too.
OP
No, I have not done a compression test. But I'm a noob with this stuff. You guys say it and I go google it. I appreciate the help
Still running like crap after 8 new gallons of gas and 16oz of seafoam
OP
I think there might be something with the timing. I verified placement of plugs and wires, but I may need to twist it one position or something. I 'm going to go look again. Thank you Mike. I'm struggling here with this one, It should be purring like a kitten.
I believe
This made me laugh. I think I have something like five timing lights in the garage. Back in the day, they were an essential tool.
Last edited:
OP
Well, ya got me. I moved each boot one position to the left. Wouldn’t even start. Put it back to where I had it and then one position to the right. Wouldn’t even start. Would I need to twist it an entire 180° perhaps? You know those bolts are just there there’s just two of them and you have to put it in one way or the other way. I know I got the rotor right. Thanks for any insight. @Squatch, you know all this! Sorry I did not tag you!
It needs to match exactly like in post #22. Moving the wires like you did will effectively throw everything off. Without a timing light, you can still adjust the timing "by ear", but that's kind of something you do when you're practiced at it. Changing the timing is done by loosening the clamp that's at the base of the distributor. There's a single bolt that you loosen. You can then retard or advance the timing by slightly rotating the distributor one way, or the other. Mark where you started with a scribed line, or something, so that you can easily return to that setting, if need be. If you do rotate the distributor, do so in very small increments, and be sure and snug down the clamp before test driving it. With the adjustments, you'll hear a change in the way it idles (rpms and smoothness), and it will behave differently when driving. But truly, a timing light is the better way to do all this.
*WRONG!
Well, hell...that's a '94 4.0 you're working on, and so all the above doesn't apply. I think yours has an ECU, and you can't adjust the timing like I described. Sorry, buddy. Sometimes my mind is stuck on old school ways of thinking.
Last edited:
JMT, one thing I advise is to try and do your best to diag without spending too much more money on it. Either rent or borrow for the remainder of tools. If the engine is mechanically shot, as in burnt valve or flat cam/cracked head, the owner will have a choice to make of repairing/replacing the engine.
Rent/borrow a compression tester. The timing on a 94 is still controlled by the computer. You would have to have an OBD 1 style computer to set the "base timing " on that YJ I believe.
If you have any brake cleaner you could spray it at all the vacuum connections to test for a vacuum leak.
Wear safety glasses.
If the owner likes the Jeep enough it could be time for the old V8 swap. Or a small diesel........
Rent/borrow a compression tester. The timing on a 94 is still controlled by the computer. You would have to have an OBD 1 style computer to set the "base timing " on that YJ I believe.
If you have any brake cleaner you could spray it at all the vacuum connections to test for a vacuum leak.
Wear safety glasses.
If the owner likes the Jeep enough it could be time for the old V8 swap. Or a small diesel........