98 xj8 217k. It either wont start or it will barely start and then die. Battery and spark are fine. Good fuel pressure at the rail. The injectors do not click. The noid light looks to flash correctly when I turn it over. I got the injectors bench tested and I heard them all click like they should.

I thought that if the noid light works, and the injectors bench test good, then they should work. I cant figure out why they are not clicking.

 

Any warning lights/codes?

 

No codes. When it does start, it is not at full idle. It will just stumble under 400rpm for a few seconds and then die. If I cut the fuel off by pushing the gas to the floor it does not even try to start, it just keeps turning over.

 

I know you said good fuel pressure but it sure sounds like a pressure problem. What is the psi reading both at start up and then off 5 minutes later.

 

A little over 40psi. The pressure is about the same after 5 minutes.

The injectors are not doing anything. I had 1 injector pulled out, but still hooked up to the harness. The harness for the next injector had a noid light in it. When I turn it over the noid light blinks, but the injector does not click or do anything.

But the same injectors click and function when bench tested.

 

Fuse 5 in passenger bulkhead box good? Swapped fuel injection relay?

 

Fuse 5 is good. I have swapped all of the relays a couple of times

 

You are moving into ECM failure territory. Might try disconnecting the battery and removing and reseating the ECM.

 

If I recall, the injectors have 12V at their connectors at all times, and the ECM switches to ground to open the injectors. If you are connecting the noid light ground to the engine block or some point other than the injector connector itself, could it be that the actual ground used by the ECM is corroded or otherwise interrupted? Not sure where that ground is on an X308 - on our XJ40 the ECM uses three different ground points, two on the intake manifold and one on the firewall. If no one else beats me to it I can look at the schematics later tonight.

If you're connecting your noid light to the two terminals of an injector connector and it lights okay but an injector won't fire, that is mysterious.

Cheers,

Don

 

I have disconnected the battery and done some hard resets. Don, it is mysterious to me also. The noid light was connected to the two terminals of an injector connector. If I put a multimeter on that same connector it is about 12v and drops to around 10v when cranking.

 

I would be looking at grounds at this point.

 

The voltage dropping to around 10v while cranking sounds suspicious. It might be worth jump-starting the Jag with another vehicle to see if the voltage still sags when cranking.

PM me your email address and I will send you the X308 electrical manual so we can discuss a few possibilities.

Cheers,

Don

 

Seeing a small voltage drop on an operating injector is normal due to the VOM not being able to track the rapid ground/open pulse from the ECM but battery voltage while cranking would be good information. A weak battery is capable of rotating the engine at a voltage below the level required by the electronics, about 10v.

 

Yeah, the term "voltage" refers to "potential difference". So, for the the ten volt measurement to have meaning, you must define across which two points you read the voltage. From the control lead to ground, the measurement is affected by the injector pulse width, as tespoint pointed out. If it was truly across the connector for the injector, that would indicate an injector that is motly on, which I doubt. If it was from the power connection of the injector to ground, it is probably just the cranking voltage drop. The correct tool for inspecting the injector voltage is an oscilloscope, since it is a pulse, and the measurement would be best across the two injector terminals.
In fact, the injector circuit apparently uses the supply voltage in the pulse calculation algorithm to adjust the pulse length to accont for voltage variations affecting the injector pull in time.

 

Yeah! That's what I meant.

 

I can confirm that according to the AJ16 Engine Management System Dealer Training Manual, the ECM monitors battery voltage and adjusts injector on-time/pulse width accordingly.

xkrmaxer, have you measured the voltage at the battery terminals while cranking, and if so, does it dip as low as 10-11V? That could definitely be the source of or a contributor to your issues.

Don

 

Thanks for the ideas guys. Don, I have been using the x308 electrical guide. Spark, I don't have a oscilloscope. I have been using a multimeter and a noid light, so I am a little limited.

Test point, I cleaned up the ems bulkhead ground. It looked fine before I touched it and cleaning did not make a difference. I am going to clean up the rest of the easily accessible grounds.

It will probably be a few days before I can get a second person to crank it while I take the measurements. I reread my post about the voltage, and I see I was a little unclear. The noid light was plugged into the 2 terminals of the harness, but with the multimeter I was putting the positive lead on the power terminal of the harness and I was just grounding the negative lead.

When I get a helper, I will get all of the voltage numbers with the key in the on position and while cranking. I will also remove the fuel pump relay and one of the injectors and make a video of the injector (removed but still plugged into the harness), next to a noid light plugged into the next harness while cranking.

Thanks again guys, hopefully I can have those voltage numbers by Monday.

 

the engine ground is between block and chassis to the right side and just forward of the bell housing.

I had one do this and it was parked on tall grass, the engine earth was shot because of it.

The engine sounds like it's initial startup is on residual gas.

 

Hi Sean,

Just for clarity, is the engine ground strap on the right side of the block when facing the rear of the car, or on the right side when sitting in the driver's seat?

Thanks,

Don

 

Driver's seat is the normal perspective.