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Old 08-08-2011, 12:09 AM   #1
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Ive got a 1994 jeep cherokee w/4.0L. it was running fine and then one day i was getting on the turnpike to come home and when i stepped on it to speed up and merge it backfired and died. now it just cranks over and wont start. at first i thought it was bad gas cause my wife and i got gas at the same place at the same time and they both quit at the same time. hers is a 99 WJ. I drained all the gas outta hers and put in a new fuel filter several bottles of heat and new plugs and hers runs fine now. mine dont even try to start or run at least hers would run alittle and cut out but my dont even try to start. ive drained all the gas out and put fresh gas in it. its getting gas to the fuel rails and ive even poured gas down the intake and it wont start or even try. I thought that maybe the timing broke but every thing turns and its getting spark. i dont know if its sparking at the rite time. i out a crank position sensor from a running jeep on it and it didnt help. i dont know what else to do or were to start i dont want to throw money at new parts and that now be it. any ideas??
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Old 08-08-2011, 12:23 AM   #2
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Compression? Bad timing belt means low/no compression
IF you think you have fuel at the rails just because its squirting out the check valve, it could just be whatevers left in the line coming out. I can't remember specs, but make sure you have proper pressure coming out (hook up pressure gauge to port), fuel injection is very picky!
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Old 08-08-2011, 12:35 AM   #3
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check your CPS as well i don't know whether 94s come with one but mine as well get that out of the puzzle .i kinda had the situation you are describing on the second day i got my 99 thought it was bad gas and had spark not strong but had spark long story short ended up being a bad CPS. hope this helps
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Old 08-08-2011, 12:47 AM   #4
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+1 on the CPS, i didn't have spark after i did a dis+rotor+spark+wires, replaced CPS, golden. I was under assumption you wouldnt get spark with bad CPS.
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Old 08-08-2011, 02:48 PM   #5
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if it was the anything with the fuel it would still start when i pour fuel down the intake and i put a different CPS off another jeep that was running and it still didnt start.
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Old 08-08-2011, 03:06 PM   #6
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If you have spark, the problem is most likely not the crank sensor.

Do you have a strong, blue, snapping spark? Yellow/orange/white indicates weak spark, which may not be strong enough to start the engine. In that case, your ignition coil is suspect.

If spark is strong and blue, then test your fuel pressure with a gauge. Without approximately 31 psi at the rail, your engine won't start.

Getting a noid light to test if the injectors are firing is also a good idea.
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Old 08-08-2011, 04:20 PM   #7
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Scan for codes. If you have codes they'll point you in the right direction. You'll have a code if it's the Crank/Cam sensor (crank sensor ultimately, I've never seen a failed cam sensor). If you have no codes at all ... keep reading.

I would dare say that the bad fuel might have killed your pump in the process.

A month ago mine died just after I filled up. Started to sputter down the road, backfired when I gave it gas. I slowly went from 60 to 30 until I pulled into a gas station. It died as I was pulling in.

I replaced the fuel pump the following week.

Find someone with a fuel pressure guage. Should read 49 +/1 at the rail during operation. Keep the gauge hooked up for a few minutes and see if it bleeds outs quickly. If not, then it's not the pump and it's not your injectors stuck open.

Since it won't crank, turn the key to the "Run" position with the gauge hooked up. It should be right around the 49 mark. You should also hear a noise (if it's quiet enough) as you turn it to run for about 1 second. that's the sound of the pump priming the fuel system.

There was someone else on there that had a similar problem and it wasn't the fuel pump for them. It was just the relay.

Before you do the gauge test, swap the "Starter" and "Fuel Pump" relays in the fuse center in your engine bay. If the starter still tries to start then you know the relay works just fine. Swap them back and test it again to make sure it still tries to start.

THEN do the fuel pressure test. You should borrow one (parts stores don't rent them that I've ever been to). To buy one is 50+. If you don't mind buying it though it's a very worthwhile troubleshooting tool to have. You only need 3 things to start a vehicle. Spark and air are easy to test. Fuel requires a gauge, and I'd say at least half the time a cherokee doesn't start it's because of a fuel pressure (and by that I mean fuel pump) issue.

I think I've answered no less than 6 other threads about fuel pumps in the last month alone. I've had to go through the process 3 times now myself so I'm getting used to the symptoms and understanding how simple it is to isolate.
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Last edited by CoffeeCommando; 08-08-2011 at 04:23 PM.
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Old 08-08-2011, 05:53 PM   #8
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The fuel pressure spec for a 98 is different than a 94. For a 94, it's 31 psi, not 49 psi.
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Old 08-08-2011, 06:06 PM   #9
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Quote:
Originally Posted by tjwalker View Post
The fuel pressure spec for a 98 is different than a 94. For a 94, it's 31 psi, not 49 psi.
Oops, forgot that. I've answered too many 97 and later questions for one day.

Isn't it supposed to be 39 PSI... as I recall when I was investigating fuel pressure and injector sizing when I was building my stroker you either had the 49 PSI or 39 PSI fuel pump. As far as the pressure at operation with them goes though I am unsure, since I didn't have a 39 PSI and wasn't concerned with which injectors they used. I would imagine if it was the 39 PSI pump it shouldn't deviate far from the mark since the way injectors operate is that they simply open... while the fuel pressure itself is what causes the burst of fuel. The injectors are just little doors that open and close, staying open for longer when more throttle (and therefore more air) is introduced to the cylinders.
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Old 08-08-2011, 06:08 PM   #10
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Quote:
Originally Posted by CoffeeCommando View Post
Since it won't crank, turn the key to the "Run" position with the gauge hooked up.

If it won't even crank your starter may not be getting power.
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Old 08-08-2011, 06:21 PM   #11
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Quote:
Originally Posted by Gee oh Dee View Post
If it won't even crank your starter may not be getting power.
I meant to say start. Even though in the context of what I was saying it doesn't really matter. The important thing is that the fuel system primes and holds, or doesn't.
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Old 08-08-2011, 07:24 PM   #12
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It cranks over it just won't start. And like I've said I pour gas down the intake and it still doesn't start so I don't believe it's the fuel system. I'm thinking something with spark. I havnt checked how strong the spark is I put an inline spark check tool on it and it's getting spark but I'm thinking it's probably not getting a very good one. The bulb was pretty dim. What would cause a week spark ?
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Old 08-10-2011, 08:13 PM   #13
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Bad ignition coil can cause weak spark. Mine had me scratching my head for a while - I had spark, fuel, compression, but no start. i finally cobbled in a different coil for test, and it fired right up. New coil = perfect running.
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Old 08-11-2011, 05:01 AM   #14
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You must observe the spark.

A weak spark is most often caused by a failing ignition coil. The coil can be tested for both primary and secondary resistances with a meter and a manual outlining the procedure.
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Old 09-14-2011, 03:51 PM   #15
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What was the fix for this? I'm having exactly the same issue.
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Old 09-14-2011, 03:51 PM
 
 
 
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