Crank no start?

AMFAMBLE

MEMBER
2002 JAGUAR XJ8
4.0L
V8
2WD
AUTOMATIC
175,000 MILES

Vehicle cranks but does not start. Got in vehicle one morning, it started, ran for about 5-sec, stuttered, then shut down. Started back and quickly shut down again. Wouldn't start after that. Scan tool showed DTC code for knock sensor. No other codes.

Checks:
Both camshaft sensors and crankshaft
sensor checked good via.
oscilloscope and resistance but none
had continuity.
Fuel pressure measured at 40psig via
gauge.
Visual spark from coils using spark test
light. Coil on plug design.

6 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Do this: see if it starts with starting fluid. If it does and then stalls, we know it is fuel related.

You already confirmed ignition spark. If it does start and then stalls, go to the fuel injectors. Each injector has a black wire with a red tracer. With the key in the run position, that wire should have power. If it does, we need to see if the PCM is providing a ground path,

Take a test light and connect the alligator clip to the battery positive. Probe the opposite wire and have a helper crank the engine. The test lamp should strobe on and off.

Let me know what you find.

Take care,

Joe

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Thursday, June 22nd, 2023 AT 8:31 PM

AMFAMBLE

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Injectors are firing so there is no need to perform the power/signal checks. I had already pulled the fuel rail out with the injectors and turned over the engine and validated that the injectors were indeed firing. Also tried starting fluid and the engine spit back through the intake, so no luck with that. So, I have fuel, air, spark, timing (i.E. Cam/crankshaft sensors are good via oscilloscope checks). Haven't done any checks on the exhaust system (don't see a need), engine compression or other potential timing issues (i.E. Jumped-timing chain), or security system (don't see a need). Going to check the gas quality (i.E. Contains water), do some compression checks and if those results are good, then I'm absolutely stuck! Don't know what else to do. Please help if you can!

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Friday, June 23rd, 2023 AT 8:05 AM

AMFAMBLE

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6 POSTS

Help.

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Friday, June 23rd, 2023 AT 8:06 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

For the engine to run, you need fuel, spark, compression, and timing. If you have all of them, the engine has no choice but to run. So, if we have spark and fuel, it is either compression or timing. You mentioned checking compression. I think that would be a good place to start at this point.

Here is a link that explains how it's done:

https://www.2carpros.com/articles/how-to-test-engine-compression

Do that and let me know what you find.

Joe

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Friday, June 23rd, 2023 AT 8:23 PM

AMFAMBLE

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6 POSTS

I was sick, so I just finally got back to working on the vehicle. Removed plugs from both side banks and engine appeared to have turned over smoothly with key start but I noticed that there was no "swoosh" sound of air being pumped from any of the spark plug holes. So, I thought this was weird. Now this was when I got sick, so nothing was done after this point until now. So today I attempted compression test and low-and-behold, the damn engine wouldn't rotate with the key start. It only clicked as if it was locked. It did not sound like a low battery clicking sound. So, I checked, and battery is good, also used a booster, still engine didn't rotate, only a strong click. Then I tried to hand rotate the engine with breaker bar using modest torque, but still engine didn't move. I plan to remove the valve covers and take a look. The timing chains are suspect. What do you think might cause what appears to be a locked or jammed engine? And ideas on what the problem might or could be?