93 Jeep Grand Cherokee - 5.2L
just put a new water pump on it now it cranks but won't start
- has fuel to the rail
- has spark
- 7.2V at the injectors
- 12V at the coil - weird because the the injectors and coil should have the same voltage - if you believe the wiring diagrams.
- when I jump across the ASD relay I get 12V at the injectors - still won't start

any help would be great
thanks

 

Wrong section. https://www.cherokeeforum.com/f5/

 

the big 3 are spark, fuel and air. Air is everywhere so that can be eliminated. So that leaves spark or fuel. If you spray starting fluid in the intake will it fire? if so then you have a fuel issue to address.

Max

 

It sounds like an electrical connection issue.

Check the grounds, including the one behind the coil on the bracket. It is shown below the © on the image.

 

If it was ok before the water pump, you upset something during the job.

 

thanks for the tips so far - this is more info on the situation.

5.7l engine 225k miles
water pump was installed, test run twice on 2 separate days to get the air out of the system - fired right up and ran fine. on the 3rd day cranks and won't start. could have backfired on the 3rd day crank.

what I have done:
1. verified spark- on the #2 cyl both at the spark plug wire and through the plug - so I have spark
2. at the #2 injector connector I get 12v on the first key position - 7.2v on the next - 11.5+/- when cranking - same readings on the field coils on the alternator.
3. put noid light on #2 injector connector and get blinking
4. fuel pressure in rail is around 40psi
5. engine will not fire when putting either gas or carb cleaner down throttle body when cranking
6. even when not doing #5 above - smell gas coming from engine
7. fuel pump relay and asd relay seem to work fine - even jumped the asd relay and nothing happened.
8. checked timing chain for TDC against #1 cyl. it seems to be in the right place.
9. cleaned all the grounds
10 the internal display sys does not work, and hasn't for some time.
11 the letters "ER" are on the heater/AC display
12 checked all the fuses that support the ignition system - they're good.
13 pulled the hose off the pcv valve - and I am getting suction in the intake manifold

I'm running out of things to check,
any help would be most appreciated

Thanks

 

"7.2V at the injectors
- 12V at the coil - weird because the the injectors and coil should have the same voltage - if you believe the wiring diagrams."
Make sure you have the right diagram, then believe it.

2. at the #2 injector connector I get 12v on the first key position - 7.2v on the next - 11.5+/- when cranking - same readings on the field coils on the alternator.
Lost me on that one, first key position is key on engine off, next is crank or start. Those are the two I know besides accessory. Either one you should have +12 at the alternator B+ terminal and the field connection.
Have you checked the battery and cable connections? What is the voltage at the B+ of the alternator in those two key positions?
Is 40 lbs the right pressure? My 97 calls for around 50. Is the pump getting +12 or is it also getting the 7 volts? I think the PCM wont work with less than 8 volts.

 

I've got 12v at the fuel pump.

I guess I'll check the injectors next to see if they are firing even though the voltage is there and the noid flashes.

Would the gas not ignite even with spark? Does the spark have to be of a certain heat or energy level?

 

so I have a 93 5.2 as well. It would start at times and run 30 seconds or so then just cut off. I would check spark and looked fine then I would check gas and that seemed fine. But long story short tried to get the thing to hit off of carb cleaner and nothing so even though I had spark off the coil I decided to swap it out. Now mind you the one I took off is less than two months old and the jeep ran great with it until this happened for me. So I picked up a coil from the junkyard that had just come in the one off the 4.0 works as well as it's the same one and now mine starts and runs perfectly. So all that to say I had spark as well just not enough. Pull a part sells coils for like 8 bucks and that fixed my issue.

 

I've kind of come around to that conclusion as well. If the spark was good the 5.2l should at least stumble with the carb cleaner. It doesn't. Will try a different coil and see what happens.

Thanks for all the help everyone.

I will post results.

 

It was the coil, the engine now starts.

Thanks to everyone out there.

 

Glad it worked out.

 

AWESOME!