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  #1  
Old 12-08-2002, 04:19 PM
will_m will_m is offline
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MPI questions.....

I asked the same thing on JU and got really no where so here is my post. Tell me your opinions:

O.k. got a YJ with an MPI kit. I think the fuel pump is going. The Jeep seems to ping and rattle a lot if I want to jump on the gas. The cat was changed less than 1,000 miles ago.

Now, I checked Hesco's site ( www.hesco.us ) and they have 2 of them. One regular replacement and one that provides higher pressure (70-90 psi.) The difference in price is $10.

Now here are my questions:

1) What is the normal pressure of and fuel pump for a 4.0L fuel pump?

2) Will using a higher pressure pump do anything bad? (This is an older engine with 130,000 + miles.)

And, on a different note:

3) What should the order of fuel delivery be?
a) fuel tank - pump - filter - engine
b) fuel tank - filter - pump - engine

Thanks for any help.
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  #2  
Old 12-08-2002, 06:43 PM
Hyperman Hyperman is offline
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Using premium?

I have the Mopar unit from HESCO on my CJ7. My initial guess is that you are not using premium. At the time the kit was designed, it was required to use 92 octane and now we can only get 91; and that with Alcohol and other weird stuff in it. Could also ping on you if you were maybe in a higher gear and lugging it. I did change to the adjustable high pressure pump from HESCO. I changed it for the couple of times I have experienced vapor lock at high elevations. This has only happened to me twice in the last four or five years I have had the kit installed and went to the pump this year. This was after an experience going up to Bristlecone Pine NF. The other time it happened was on the long pull out of Ourey to Silverton, Colorado. It could also be timing or possibly even an O2 sensor issue. As far as the pressure issue, I believe the requirement is like 31-38 psi. I think the adjustable comes from HESCO at 42 psi. I would go down to your favorite auto parts store and buy a fuel pressure gauge that hooks up to the Schrader Valve on the fuel rail.
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  #3  
Old 12-08-2002, 06:50 PM
will_m will_m is offline
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I was thinking of the of the fuel pressure gauge but will this work when the Jeep is at a standstill? The pinging happens at speed and under load.
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  #4  
Old 12-08-2002, 07:05 PM
Art Welch Art Welch is offline
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With a longer hose you can run the fuel pressure gauge into the cab and observe it as the problem occurs.
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  #5  
Old 12-09-2002, 08:07 AM
Bruce David Bruce David is offline
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Re: MPI questions.....

Quote:
Originally posted by will_m
I asked the same thing on JU and got really no where so here is my post. Tell me your opinions:

O.k. got a YJ with an MPI kit. I think the fuel pump is going. The Jeep seems to ping and rattle a lot if I want to jump on the gas. The cat was changed less than 1,000 miles ago.

You can retard the timeing 2 degrees by putting washers between the CPS braket and the oil pan.

Now, I checked Hesco's site ( www.hesco.us ) and they have 2 of them. One regular replacement and one that provides higher pressure (70-90 psi.) The difference in price is $10.

Now here are my questions:

1) What is the normal pressure of and fuel pump for a 4.0L fuel pump?

The pressure at the rail under full throttle is 40psi+

2) Will using a higher pressure pump do anything bad? (This is an older engine with 130,000 + miles.)

Don't know the answer to that one

And, on a different note:

3) What should the order of fuel delivery be?
a) fuel tank - pump - filter - engine
b) fuel tank - filter - pump - engine

fuel tank - pre filter(Nappa #18-7831) - pump - filter - engine

Thanks for any help.
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  #6  
Old 01-01-2003, 10:00 AM
will_m will_m is offline
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UPDATE

Well, I called Hesco and they said I didn't really need to add the higher pressure fuel pump as it wouldn't do much. They did suggest replacing the O2 sensor, spark plugs and fuel filter. I also had a severly bad grommet on the valve cover. All were changed. While I got a little better performance (able to hit and maintain 65MPH), I still have some sluggishness.

Should I go for the fuel pump replacement?
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  #7  
Old 01-02-2003, 11:08 AM
Cement_guy Cement_guy is offline
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I believe any pressure higher than the regulator is set forwill just route fuel back to the tank. Is the problem only during high throttle demands ie, more than half throttle on the freeway? How does it run at 35 mph? How about a flow problem due to a restricted (partially plugged) filter?
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  #8  
Old 01-02-2003, 06:31 PM
will_m will_m is offline
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It is mostly at high speed and under load (going up slight hills and under acceleration.) The fuel filter has already been changed. I am going to see if I can get a fuel pressure gauge and see what that says.

I also just found out the fan clutch has siezed so the fan spins with the engine.
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  #9  
Old 01-03-2003, 11:08 AM
Cement_guy Cement_guy is offline
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Hmm, high demand only type starve should mean there's a flow restriction somewhere...................good luck, Ken
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  #10  
Old 01-03-2003, 04:57 PM
will_m will_m is offline
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What about this....I was told by a guy at Advanced Auto Parts to look for and disconnect a knock sensor. Is there one on a 94YJ? If so I wonder where it is on the MPI kit since the kit itself is based on a 94 4.0L.
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  #11  
Old 01-08-2003, 11:00 AM
Bruce David Bruce David is offline
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No Knock Sensor on the MPI kit..
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  #12  
Old 01-28-2003, 05:25 PM
will_m will_m is offline
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O.k. slight update.

While doing a radiator flush (was freezing my lower radiator hose during the cold and lost my heating...BRRRR), I noticed the fan clutch has seized. The fan is frozen to the clutch. CVould this be causing a problem?

Also, decided to fill up with 89 octane instead of my normal 87 and it ran slightly better under hard accelaration from a standstill to highway speeds yet I still get a knock or "miss" when I push it.

When it gets warmer, I will hook up the check engine light and tach. I also got a fuel pressure gauge but haven't used it yet.
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  #13  
Old 01-31-2003, 09:21 AM
Bruce David Bruce David is offline
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91 octane is required with the MPI kit...........
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  #14  
Old 01-31-2003, 09:26 AM
will_m will_m is offline
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Quote:
Originally posted by Bruce David
91 octane is required with the MPI kit...........
I thought that too but I called Hesco and they said it did not plus it ran great for 9 months on 87 so something else has changed.
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