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Rebuilt 4.0 cranks but won’t start!! Is mechanical Timing off?
Ok, everyone. I’m new to this board but have had many an xj. I currently have a ‘99 XJ 4.0 with ax15 manual. Motor dropped a piston skirt at 192k and I pulled it and had it rebuilt (bored .020, new pistons, machined crank, new cam, timing chain/gears, valve job etc.). When I pulled it it ran. Now that it’s been rebuilt at a dear price...it doesn’t. It only cranks and sounds like it wants to fire here and there but never does. I’ve set distributor multiple times to TDC position (on compression stroke)...every time the rotor lands just shy of 6 o’clock - almost pointing to the little boss on the distributor housing. Seems a bit advanced compared to pics I’ve seen where it’s more 5-5:30 range - but that’s the only way it goes when you pin it with a drift punch like you’re supposed to at install. i have run all the diagnostics during startup and have no circuits unaccounted for. Crank is there, Cam position etc. I have excellent spark and fuel pressure along with injector pulse. Plugs are soaked in gasoline when I take them out. Spraying ether into the intake does nothing. My question is - is it time for me to call the engine builder and question the accuracy of his mechanical timing? It seems like such a no-brainer to be able to get this right on a 4.0 if you’ve been building engines for any length of time....but I’m out of any other ideas. |
I ran into a similar problem when I did my timing. Mine turned out to be that I used the wrong timing chain set. People told me that it didn't matter but once i switched the chain and sprockets my XJ fired right up. The difference was the number of pins on the chain and the spacing between teeth on the gears. I put a 92 motor into my 94 and ordered my timing set for a 94. I had to go back and order a timing set for a 92 and bam. But also if the guy didn't line up the marks correctly when installing the timing set there may be a problem but if it was at a shop id hope that wouldn't be the case.
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Originally Posted by garran99
(Post 3529155)
t if it was at a shop id hope that wouldn't be the case.
I had a shop I once trusted, but several months ago I took my driveshaft in to have them do the u-joints (since I didn't want to deal with them), they handed me back the shaft. Immediately I noticed they'd boogered up the ends where the snap rings went into. That was infuriating since it was one of the reasons I was willing to have the shop do the job. I moved the joints and noticed that one of the joints was not rotating smoothly. I thought to myself - ok, they had trouble getting the old joints out but they wouldn't possibly hand me back the driveshaft with the u-joint installed incorrectly. Wrong. I went against my gut and installed it and took the Jeep for a test drive. About 300 feet out of the driveway the Jeep is driving wonky and as I turn around to bring it home - BANG - the driveshaft sheared off the strap bolts and the whole shaft fell out. I grabbed the shaft and put it in 4wd to get it back into the driveway and ended up replacing the u-joints myself in the end anyway. So much for the "professional shop work" on that one. I think they fired the guy shortly thereafter, but I now have doubt about that shop. I took the Jeep there for inspection last month, but if/when I need to have work done, I'm going somewhere else. Fortunately I discovered there's a 4wd specialty shop (aka a Jeep shop) about the same distance as my previously trusted shop. So hopefully between that shop, my trusted frame/welder and my trusted tire shop, I should be covered for anything that I can't or won't do myself. |
Yeah, I hope he used the right timing set. I’m going to check compression just to see if it’s below spec (as I would suspect if it’s out of time). After that it’s going to be me pulling everything back apart in my garage to get down to the chain for a visual. It really is infuriating though. The reason I spent the money to have it rebuilt in the first place was so that I wouldn’t be grappling with my own amateur-hour shenanigans (after all - I haven’t been building engines for 20 years like this guy supposedly has)....and in the end the guy might have been slapping in that cam sprocket with a fifth of gin in him. |
Check your firing order ! Check fuel pressure , check compression , check for spark ... report back ! |
Originally Posted by GreaseMonkey17
(Post 3529279)
Check your firing order ! Check fuel pressure , check compression , check for spark ... report back ! |
Originally Posted by Detroit XJ
(Post 3529277)
Yeah, I hope he used the right timing set. I’m going to check compression just to see if it’s below spec (as I would suspect if it’s out of time). After that it’s going to be me pulling everything back apart in my garage to get down to the chain for a visual. It really is infuriating though. The reason I spent the money to have it rebuilt in the first place was so that I wouldn’t be grappling with my own amateur-hour shenanigans (after all - I haven’t been building engines for 20 years like this guy supposedly has)....and in the end the guy might have been slapping in that cam sprocket with a fifth of gin in him. The only thing I'd say is that folks seem to have a hell of a time with getting the distributor indexed correctly. Apparently it's a tooth off the mark that the "spec" indicates. I've never dealt with this personally, but if I found myself in your position, I'd at a minimum be researching the hell out of that as a possibility before going to all the work of pulling the timing cover off. As I've never dealt with that sort of thing myself, I don't know if it's something that you can maybe "try and see" easily or not, but if so, it may be worth a try. Perhaps you should get yourself a fifth of gin (or whatever your beverage of choice is) for when you finally get it fired up! :) :) |
Compression report
So, as suspected....compression is way low all down the line. Even accounting for cold cranking and pistons that haven’t seated...it’s not even close on 5 out of 6 pistons. Here’s what the test showed: #1 50psi #2 82psi #3 69psi #4 63psi #5 70psi #6 105psi so....somebody’s going to either give me my money back or come and pick this vehicle up and fix it. So annoying. Wife is having major surgery in two weeks and my window to fix this is growing very small. |
Originally Posted by PatHenry
(Post 3529359)
It could be as simple as the wrong timing set, but since it "fit" he went ahead with it.
The only thing I'd say is that folks seem to have a hell of a time with getting the distributor indexed correctly. Apparently it's a tooth off the mark that the "spec" indicates. I've never dealt with this personally, but if I found myself in your position, I'd at a minimum be researching the hell out of that as a possibility before going to all the work of pulling the timing cover off. As I've never dealt with that sort of thing myself, I don't know if it's something that you can maybe "try and see" easily or not, but if so, it may be worth a try. Perhaps you should get yourself a fifth of gin (or whatever your beverage of choice is) for when you finally get it fired up! :) :) Funny you mention that. The distributor was my first subtle clue that something was rotten in the state of Denmark. It was ever so slightly misaligned to the bolt hole in the block when the cam sensor reluctor was locked to the housing in proper relationship. I even tried installing it on the next tooth back and it wouldn’t phase properly. It also looked like it would land a little in front of or a little behind where the YouTube vids show. |
I would definitely be making angry phone calls with those compression readings on a freshly rebuilt engine.
One can hope it's just a misaligned timing chain, but even if so, if the comparably simple task of lining up dots on gears was screwed up, what other things were half-assed? I know very little about engine rebuilding, but it seems like there are a lot of precision measurements that have to be correct. |
Sorry to hear that! Best of luck with the shop owning up to their bad work . |
Plug wires are in the right order?
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Originally Posted by PatHenry
(Post 3529516)
I would definitely be making angry phone calls with those compression readings on a freshly rebuilt engine.
One can hope it's just a misaligned timing chain, but even if so, if the comparably simple task of lining up dots on gears was screwed up, what other things were half-assed? I know very little about engine rebuilding, but it seems like there are a lot of precision measurements that have to be correct. This is is my thought too. Even after we get the motor running, what other snakes might be the in the woodpile from an imprecise build? The good news is that they came to my house and picked the Jeep up on a flatbed today after I spoke with one of the shop owners this afternoon. They agreed to take a look and if it’s their work that is the issue they would take care of it. So I’m cautiously optimistic. |
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