Red4Litre

91 XJ 4.0 AW4/231 190k Sorry for the long winded description, but I want it to be clear as possible

Just bought this and I'm having some problems diagnosing this. Basically it will take a bit longer to start when cold now, and when it's shut off at operating temperature it usually won't restart on it's own until It cools down or I spray starting fluid in the intake. If I use starting fluid it will run normally with one exception: If I give I give about 75% throttle or more from a standstill it will lurch as if someone turned off the key, then roar forward and take off or it will stall. This happens both hot and cold now, except when it's cold it will restart.

So long crank time when cold, usually not starting when hot (without starter fluid) It would seem like I have spark at all times since it will always run (and even continue to run) with starting fluid. I do not have someone to crank the engine over while I'm under the hood though..

What I've done:
Fuel pressure is ok
40psi during crank (when it won't start and when it will)
31 psi hot idle with FPR connected
39 psi hot idle with FPR vacuum line disconnected.
Cleaned grounds and battery terminals
Replaced CTS a week or so ago (Fan was coming on too late)

Injectors and CPS were replaced by the previous owner. Possibly used parts.

No difference in how it starts if the CPS/IAT sensors are connected or disconnected beyond the check engine light illuminating.

Any tips guys? I'm sharing this car with my girlfriend and I really don't feel so hot about letting her drive it the way it is

93gc40

I'm thinking dirty sticking injectors and a little heat soaking. Is it holding any fuel pressure when shut off? How do the plugs and cap and rotor look, good spark?

Red4Litre

Plugs have a bit of a tan color to them but nothing abnormal. It seems to hold pressure.. When I turn it off the gauge creeps up from 31 to 40..Hangs there for about ten seconds then drops back to 30 within five mins and was reading ten about 20 minutes later (I went in for a sandwhich.)

It does build pressure very nicely though. As soon as I turn the key to on its at 30, if i cycle it it will go to 40.

Doubt it will work but I'll go and run some injector cleaner through it and see if it makes a difference. Only 1/4 tank of gas left so it should be concentrated. Thanks for the response!

Edit: Will check spark as well

Red4Litre

Okay, ran some injector cleaner through and drove about 20 miles. Ran fine (i was gentle,) except it wouldn't restart when I turned it off. Restarted it with starting spray and gave it full throttle from a start and it promptly lurched forward twice then stalled. After I got it restarted I noticed I can use the skinny pedal as much as I like in reverse but not forward gears?? Can also go WOT in neutral and park without it dying.

Wouldn't restart again. So right now when it's not starting, I do have good, blue spark. Swapped fuel pump relays with the A/C for good measure, no difference. Same with the ballast resistor jumped and connected.

Ran a quick fuel test and while the engine is cranking this time I noticed the fuel pressure will intermittently quickly jump from 40-30psi. I may have just noticed it but I hadn't seen it earlier.. Is this the injectors opening and closing?

Red4Litre

A-ha! All the messing around I did with the sensors was before I disconnected the battery for about ten minutes, so any of those codes that were set should be cleared..

I just ran out and did the key on/off thing and I got a number of them..But still no CEL with engine on.
12-Battery disconnected (haha theres a code for this?)
21-Oxygen sensor or circuit (According to haynes..)
54-Distributor sync pickup (AKA cam sensor? haynes says to simply replace it?!)
55-End of code output

I may disco the battery again and see what comes back up, but the cam sensor sounds about right.. Fails when hot and isn't giving the ECM any input to run the fuel injectors? May explain the no-start when hot but not sure about why it cuts out at high throttle/high load. And why didn't any of these trigger the CEL?

Red4Litre

Reset ECM, no codes this time. Now it won't start at all without starting fluid. Runs good until you hit 3/4 throttle in a forward gear then it will quit. Won't restart under any conditions without starting fluid. Might get a few fires here and there but not enough to get it going.

I've had a cracked (or broken) flexplate for about two weeks now and just taking a look under there today I can now see the flexplate where it bolts to the crank. The lower part of it anyway.. I'm missing a few bolts by the looks of it (I can see empty holes) and my 'rod knock' is now certainly the flexplate. Since I can see it I'd assume some bellhousing bolts are missing as well.

So, this jeep is parked until I can get together enough money for a shop or expanding my tool collection. I suspect it may be moving around enough to screw with the CPS a bit, but that doesn't make sense since it will always fire up with starting fluid.

Oh yeah, the PO replaced the flexplate with a used one last year.