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Crank no start..

MechanicalType

NAXJA Forum User
Location
TN
First time poster, first time XJ owner. Jeep won't start. Cranks all day, shows only code 12 and 33. Fuel pump kicks on for about 1/2 second when ignition is keyed on, Schrader valve releases decent fuel pressure. Unplugged MAP sensor, checked ASD relay, checked fuel pump relay. I understand the ASD is switched to ground.

Fuel pump relay has power to all 3 prongs, 4th prong (green/white) gets battery voltage when cranking. You can unplug the crank sensor and plug it back in w/ key on engine off and hear the pressure build in the fuel feed line. Crank the key and it's pumping fuel, distributor is getting spark.

I can get the engine running with a very small spritz of ether and it will sit and run until I shut it off. I've cranked it with the fuel line in a jug and it pumps plenty of fuel. I tried swapping out the crank sensor (compared resistance of old and new and barely any difference) installed it anyways, still no luck. spritzed a bit of ether, pedal to the floor, fired up and has been idling and revving to 3500rpm w/out any sputter or misfire.

Anyone have an idea? At first I thought it was sucking air, but it seems to have plenty of fuel w/out aeration when cranking. Possibly a MAF or tps sensor? Anyone have any idea how to test them?

Note: Ether is bad, mmkay..

Note: yes, I know ether bad, but it's was just a one time thing.. Guess I've been a diesel mechanic too long.


Thanks in advance,
Mechanicaltype
 
Specs on the vehicle would be good. Year, engine and transmission at least. There are some differences which matter.

Could this be an ignition problem? I have not played around with ether, but could it be that ether ignites more easily and gets things running where a weak spark is unable to ignite the gasoline?
 
Any chance you have a leaking injector and your starting flooded?

You say you have pressure, has it been measured after this ether start, while running, then checked for bleed down?
 
My apologies. 94 Cherokee 4.0L. Haven’t ran a fuel pressure test on the engine. Just verified fuel delivery. Occasionally it will randomly start on its own with no ether assist. But then you run it a while (not driving, just idling in driveway) and then as soon as you shut it off, won’t start next time without ether.


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Ether (starting fluid) ignites more easily than gasoline. I seem to be getting consistent spark from the coil and distributor.

Also, 4.0L auto trans 4wd.


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It sounds like your fuel isn't atomizing well enough. I would first be looking to ensure fuel pressure is at the correct pressure. Low pressure could be caused by:


1) dirty fuel filter
2) failing fuel pump
3) failing fuel regulator valve


If the pressure checks out I would start looking at the injectors.
 
Not arguing your advice, but I am curious as to why it would run perfectly after it finally gets started if the pressure was low?


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I am wondering if it could not be voltage related somehow, and the operation of the alternator is the key to its ability to run.
 
I thought the same about voltage. I charged my battery and even tried boosting it with a commercial booster (up to 250A , 6/12/24v) with no change.


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I’ll run with 4x4jeepmanthing’s injector comment and try to unplug an injector at a time to see if I get any change.


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Not arguing your advice, but I am curious as to why it would run perfectly after it finally gets started if the pressure was low?


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It may sound ok but may not be running perfectly. If the fuel isn't atomizing properly it may still be able to shoot a stream of fuel into the cylinder. When cold, the engine would simply flood but once that cylinder is heated up by the ether blast, it may be hot enough to keep running but perhaps not as efficiently. I have seen this kind of thing with a bad relief valve. The valve was holding some pressure but not enough so it was a bear to start but would seem to be ok after you got it going. Problem was that once I took it out on the road, it lacked power.



The challenge I have is that if it starts after an ether blast it doesn't make sense that it is a power issue plus you said that you have good spark. An engine needs only 3 things to start: Spark, Fuel and Compression. It wouldn't hurt to do a quick compression test to see if you have a blown head gasket but a pressure test on the fuel system is also a good idea.


FWIW, I am in the process of rebuilding a high performance engine that blew a head bolt and lost all compression on cylinder 1. Went to start it a couple of weeks ago and it was uncharacteristically tough to start but once started it "sounded normal". I crawled under the car and found the top of my head bolt.


You have spark so strike that off the list. The next step needs to be to confirm fuel and compression.


HTH
Todd
 
I’ll run a compression test. I just replaced the head gasket with a severe duty fel pro one. Followed torque spec and sequence, etc. I’ll be working on it a bit over the weekend. I’ll update you guys if I make any progress.


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Maybe a bad fuel pump ballast resistor? You can bypass it (it's only there to lower voltage to the pump because owners were complaining about fuel pump noise), and see if the no start issue returns.

I had one in my '92 until it started breaking apart due to age, at which point I inline-spliced the two wires together and threw the remains of the resistor away.
 
I’ve got to check fuel pump voltage. Got 6 or 7 other jobs going on right now ontop of the day job, I forgot to do that. Ack. I know I’m getting battery voltage on the out side of the pump relay. I’ll check for voltage drop. The pump has a super short burst upon key on engine off. Usually pumps prime for 1-2 seconds, this one primes for a half a second at most.

Thanks for the ideas guys, got a trans to tear down and I’ll hop back on the Jeep.


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I’ll run a compression test. I just replaced the head gasket with a severe duty fel pro one. Followed torque spec and sequence, etc. I’ll be working on it a bit over the weekend. I’ll update you guys if I make any progress.


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When you installed the new head gasket did you put thread sealer on that one bolt that extends into the water jacket?
 
Finally got around to this past weekend. Fuel pump is getting full battery voltage on cranking. I jumped power to the pump to help prime it on key on and it fired right up. I shut it off and it started a few times no issues, then it started taking longer and longer. I’ve realized if I pump the pedal (i.e. carb engine style) it seems to fire over on its own after a few seconds. Without touching the throttle it won’t fire at all. Flaking TPS?


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Haven't worked on the jeep in a while. Got an SRT4 so it's gotten most of my attention along with a bathroom remodel. Noticed my kick down cable was frayed badly, replaced it. Cleaned the interior up a little, test drove it and it would red line before shifting. 3rd wouldn't take until about 75-80mph which prompted the kick down cable inspection/adjustment.



Started reading and realized the TPS could be the culprit. Unplugged the TPS to take it for a drive to test this theory (as the reading wasn't far off from what it should be, voltage wise and it increased the more I opened the throttle in small increments) and I'll be damned it started up immediately.



Test drove it, no change. Plugged the old TPS back in, crank no start w/out throttle. Unplugged it, fired right up. Decided I'd throw a used TPS on it, snagged one from the junkyard, fixed the crank/no start issue AND the shifting issues. Woo!



Thanks for all the responses and suggestions. It's running great and ready to hit the trails again!
 
Could you bleed the pressure out of the line at the check valve on fuel rail after running it hot, and see if it starts better that way.....
Might help pin point the problem a bit more if it dose?
 
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