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Technical Forum The main forum for jeep related discussions. Mechanically Inept... |
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#1
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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. |
#2
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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
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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
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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
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Re: MPI questions.....
Quote:
__________________
Bruce Its just a sign of the times,,,,,,,,,,,, Going forward,,,in reverse,,,,,, ___________________________ ------------------------------------------- fourtreks.com |
#6
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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? |
#7
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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?
__________________
"Having a wife and children and working to keep them in comfort has ruined far more men than wine and harlots ever did" 2001 Sport, D44, NV3550, Rancho R/C, 8274 32X11.50 KM's on Canyons. |
#8
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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. |
#9
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Hmm, high demand only type starve should mean there's a flow restriction somewhere...................good luck, Ken
__________________
"Having a wife and children and working to keep them in comfort has ruined far more men than wine and harlots ever did" 2001 Sport, D44, NV3550, Rancho R/C, 8274 32X11.50 KM's on Canyons. |
#10
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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
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No Knock Sensor on the MPI kit..
__________________
Bruce Its just a sign of the times,,,,,,,,,,,, Going forward,,,in reverse,,,,,, ___________________________ ------------------------------------------- fourtreks.com |
#12
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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. |
#13
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91 octane is required with the MPI kit...........
__________________
Bruce Its just a sign of the times,,,,,,,,,,,, Going forward,,,in reverse,,,,,, ___________________________ ------------------------------------------- fourtreks.com |
#14
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Quote:
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