(SOLVED) XJ Fuel Pressure/Injector Question - Page 2 - JeepForum.com
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post #16 of 31 Old 03-08-2017, 07:38 PM
CP30
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I figured you probably already did this but I would change out the fuel filter if you haven't already done it. Can't hurt. They're relatively cheap and you're supposed to change them out every like 30,000 miles anyway.

I think your hold pressure on your fuel is probably fine. The Haynes manual for my Ford Mustang says that the fuel pressure should not drop more than 5 PSI within five minutes after cutting off the engine. That infers that the pressure will normally drop at a certain rate after you cut the engine.Your hold pressure sounds in line with that.

I suspect things in this order:

Fuel
Fire/spark
Air
Compression/Head gasket

There are many sensors that tell the ECU how much fuel needs to be sprayed by the injectors and that control the spark timing. I wish you were actually getting a check engine light. That would at least narrow it down. BTW, have you actually checked your data terminal with a scanner yet? Maybe your CEL is burned out. (Mine is burned out on my ford pickup. Gotta replace it) When your turn your key to the ignition on position does your CEL light up briefly?

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post #17 of 31 Old 03-08-2017, 08:17 PM Thread Starter
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I wish I had a check engine light...but no, and it does work.
I have even scanned for codes and nothing pending.
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post #18 of 31 Old 03-08-2017, 08:40 PM
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I was wondering, do you have EFI or a distributer? (Got a distributer on our 96 XJ). If you have a distributer I would change out the rotor and the cap. More cheap tries. Not trying to give spam answers. Just throwing out things I would try to do if it were mine.
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post #19 of 31 Old 03-09-2017, 05:49 AM
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I don't believe the fuel pump is supposed to continue to run for more than a few seconds with the key in the "run" position if the engine is not running. I know mine won't (hence why people suggest cycling a few times if you have a check valve issue, instead of holding it there). So if leaving it there for an extended period helps, I would guess electrical issues, not fuel pressure issues.

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perfect depends on how far away you are when you look at it:D
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It's a 4.0 ... as long as there's something in the crank case that isn't coolant I'm sure it will still run forever.
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post #20 of 31 Old 03-09-2017, 08:37 AM
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Quote:
Originally Posted by Kettles View Post
I don't believe the fuel pump is supposed to continue to run for more than a few seconds with the key in the "run" position if the engine is not running. I know mine won't (hence why people suggest cycling a few times if you have a check valve issue, instead of holding it there). So if leaving it there for an extended period helps, I would guess electrical issues, not fuel pressure issues.
Unless theres a difference in behavior on the older ones it runs until it builds to operating pressure, that just usually only takes a couple of seconds

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post #21 of 31 Old 03-09-2017, 08:52 AM
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Quote:
Originally Posted by Kettles View Post
I don't believe the fuel pump is supposed to continue to run for more than a few seconds with the key in the "run" position if the engine is not running. I know mine won't (hence why people suggest cycling a few times if you have a check valve issue, instead of holding it there). So if leaving it there for an extended period helps, I would guess electrical issues, not fuel pressure issues.
I think the way to eliminate the fuel question would be to take off air intake tube from the throttle body opening, from a cold start, have someone open the throttle up and turn the key to start it and spray carb/throttle body cleaner into the throttle body opening while someone tries to start it. If it starts right up that means it wasn't getting fuel. If it still is hard to start and keeps cranking and cranking then you can eliminate fuel. It's a spark and/or air issue. And that most likely would be a bad sensor feeding bad info to the ECM. Or the ECM itself has got a problem.

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post #22 of 31 Old 03-09-2017, 09:11 AM
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Originally Posted by CP30 View Post

I think the way to eliminate the fuel question would be to take off air intake tube from the throttle body opening, from a cold start, have someone open the throttle up and turn the key to start it and spray carb/throttle body cleaner into the throttle bottle body opening while someone tries to start it. If it starts right up that means it wasn't getting fuel. If it still is hard to start and keeps cranking and cranking then you can eliminate fuel. It's a spark and/or air issue. And that most likely would be a bad sensor feeding bad info to the ECM. Or the ECM itself has got a problem.
We know from OP's pressure tests that fuel pressure isn't being maintained, a starter fluid test isn't necessary to know there's an issue there

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post #23 of 31 Old 03-09-2017, 05:14 PM
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Originally Posted by bluejunior View Post
Unless theres a difference in behavior on the older ones it runs until it builds to operating pressure, that just usually only takes a couple of seconds
The pump runs for a period of TIME. There is no fuel pressure sensor.

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post #24 of 31 Old 03-09-2017, 05:55 PM
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The pump runs for a period of TIME. There is no fuel pressure sensor.
Okay. Mine ran longer with the bad check valve. I assumed it was an overload controlled by the PCM based on the amount of current being drawn by the fuel pump to continue increasing pressure. I know there's not a dedicated fuel pressure sensor.

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post #25 of 31 Old 03-12-2017, 02:32 PM Thread Starter
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Changed the injectors Saturday and still had hard starting. One plus is when the jeep runs it runs smoother than before with the new injectors.
So next I pulled the new Bosch pump, returned it and got a new Bosch from autozone. Still long crank...maybe quicker than before but still not right. It does seem to be holding fuel pressure correctly now.
So I guess next step is to check the spark...waiting until my brother comes over and one of us will crank while the other watches the spark.

BUT...this afternoon when I was done putting the pump in I attempted to start it and my ignition switch or cylinder broke. The key spins way past the start position with no resistance.
Am I looking at replacing the cylinder or the switch? Or both?

Thanks everyone
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post #26 of 31 Old 03-15-2017, 06:36 PM Thread Starter
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It was the cylinder...swapped it out today.

Next, tackling the long start issue....I'm stumped but not ready to give up.
Will do some more testing this weekend.
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post #27 of 31 Old 03-15-2017, 06:41 PM
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It was the cylinder...swapped it out today.

Next, tackling the long start issue....I'm stumped but not ready to give up.
Will do some more testing this weekend.
Longer start is usually the check valve on the fuel pump, checked that yet?

If not, spend the extra for Bosch. Airtex (which is also repackaged as the store brand for major chains) is known to be a crap part and you'll be replacing it in a year.

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post #28 of 31 Old 03-15-2017, 06:51 PM Thread Starter
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Originally Posted by bluejunior View Post
Longer start is usually the check valve on the fuel pump, checked that yet?

If not, spend the extra for Bosch. Airtex (which is also repackaged as the store brand for major chains) is known to be a crap part and you'll be replacing it in a year.
If you remember that was the first thing I did...brand new bosch....then pulled it and exchanged with another new bosch just in case.
Still no go.
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post #29 of 31 Old 03-15-2017, 07:20 PM
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Originally Posted by dan4081 View Post

If you remember that was the first thing I did...brand new bosch....then pulled it and exchanged with another new bosch just in case.
Still no go.
Sorry, mixed up threads. I'm on a lot lol

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post #30 of 31 Old 03-15-2017, 08:20 PM Thread Starter
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Sorry, mixed up threads. I'm on a lot lol
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