Starting troubles....

Alright, I'm back to having troubles with my '91 XJ. I got the engine swap out of my old '91 done successfully. It was running great for a few months, then just a few days ago, I stopped at the bank, and when I came back out, it wouldn't start. I towed it home with my procomp tow strap and my friends bronco (pity, a jeep being towed by a ford...), and began work. Here's a list of things I've replaced in my amateur troubleshooting attempts:
new bosch platinum quadra spark plugs
new spark plug wiring
new distributor cap and rotor
new fuel filter
new Crankshaft Positioning Sensor (CPS)
My solenoid works, my starter works, my fuel pump works, and I'm getting fuel at the rail. Me and my Hayne's manual are running out of idea, and I'm starting to get frustrated. Here's what happens; I crank the engine, and it tries to turn over, or does so successfully, but shuts off directly thereafter. If I give it gas when it turns over, it'll rev real high, then when the R's drop back to normal, it shuts off again.
PLEASE HELP
Thanks in advance guys

This is a wild guess, but have you checked the AIS and TPS? Is the TB clean? The reason for the questions is that it sounds like you can start it but it won't idle, right?
How about the MAP? is the vacuum line attached, connector good?

possible vacuum leak?

Definately sounds like either a vacuum leak or the TPS is hosed. Have you washed the engine lately? That is a kiss of death for the TPS if you are not careful.

I had experienced this same problem with my friends WJ while camping one night. The battery went dead while running 12v accessories for hours and we had to jump it, but as soon as it started it would die and if we gave it gas to keep it running the RPM's would jump by itself then it would die again. We disconnected the battery to reset the computer but it still happened. He just tried to keep it running and he was able to just drive it back while i followed him in my XJ. I suspect the battery, alternator, coil or computer. You should have the battery and alternator checked out. MOST auto part places test alternators and batteries for you at no charge. Oh and get at least a Chilton's Manual it seems to cover much more then the Hayne's and if you can a FSM would be best. I had to have all three and it all helps, believe me!

Matt

Thanks guys, I'll check through all of those probs then get back to you guys...
Until then...well...I'll keep whacking my forehead against the hood.

Alright, here's the evidence of my innate ignorance...how do I check for a vacuum leak, and if one is present, how do I fix it, and could that really be the problem keeping it from running. There, alot of annoying questions. Anyone who can answer them would be majorly appreciated.

back in '91 there were many problems with ignition coils. have you tried one?

i would rule out a vacuum leak. not likely after turning off your engine. i would also rule out any symptoms a wj had. they are two entirely different animals. when the wj batteries die for an extended peroid of time the pcm loses the idle memory and it takes a few minutes to learn. you never lost battery power anyway.

Here are some ideas you might find useful:

Have someone start it and rev it just enough to keep it running.

- Do you hear any hissing or whistling sounds? Try to locate it.

- There are only a few vacuum lines off the manifold, but some affect engine ops. Try disconnecting (engine off) and plugging each at the source (manifold), starting with the brake booster line and see if it idles again. Don't disconnect the MAP sensor line though.

- You can also take a vacuum gauge/pump and take each line, while engine off, and pump it down to about 15" of vacuum and see if it holds. MAP sensor too this time. If you can't get a line to stay down, it might be suspect. However, on one or two, like the EGR, the ECU may control it and leave the line open with engine off, so just disconnect and plug any lines you suspect with this test and try the engine on.

- While cold, but started, pour water on the manifold gasket area and see if it gets sucked in real fast at any point - a vac. leak. Also good for the throttle body base. You may have to help it 'pool' in places to see if it sucks in.

- If you suspect a leak from a line connector, like those brittle nylon/plastic vac lines, dip the connector in a bowl of water while running and see if it gets sucked dry.

- Some lines tee off to many lines after coming from the manifold. Use the vac pump test or the plug test, and if you find it's one of these lines, work your way through each branch, including the connectors to find it.

- And maybe first, do a visual check for any dangling hoses, ports onthe manifold left open, or cracked or dry hoses. Chances are, with the swap and other work, a line was pulled out some and vibration finally made it fall off.
A common vacuum leak are seems to be the vacuum reservoir, possibly behind the bumper in the 91.

- And finally, use a vacuum gauge to see if you're pulling a vacuum while cranking. It won't be as great as normal running vacuum, but if you have a mondo leak, you may show next to nothing there. If you have good cranking vacuum, and it stays while running, maybe it's something else.

- OK, one more, but this depends on if a 91 uses a mass airflow sensor. If NOT, like the pre-90 ones, I'm pretty sure that if you had a decent vacuum leak I would be able to seal off the air intake to the throttle body (board with foam pad on it) and see if it tries to run. It probably wont' be smooth, but would compensate for the leak if it was there. On a flooded engine, you can remove a large vacuum hose to let it get more air, so this is the reverse. Just make sure you seal it tight.

Another idea, if not a vac leak, would be to try the key on-off-on-off-on routine and see if there any codes for sensors. I think the 91's could flash the engine light for codes, unlike the 88-90 ones :-(