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fuel pump question

Performance mods and Advanced Stroker discussion.
rammit11
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Posts: 114
Joined: April 27th, 2010, 4:29 pm
Stroker Displacement: 4.6
Vehicle Year: 1998
Vehicle Make: jeep
Vehicle Model: cherokee
Location: southeastern pennsylvania

fuel pump question

Postby rammit11 » November 1st, 2017, 6:44 pm

Hi, having an interesting issue with my stroker (4.6 , 9.2 compression , 62 mm throttle body,ford 24lb injectors,colder range ngk plugs ,190 tstat) . I have a 1998 cherokee that when fuel tank is full runs very well, but when around 1/2 tank or lower seems run a bit off has a detonation/ping going to half to 3/4 throttle under medium load at 2000 rpm. Afr is in the 14-15 range at this point(still in closed loop and when in open loop runs around 13) . I am wondering if the fuel pump is not meeting the requirements of the injectors. I replaced the pump when I installed the engine and the pinging issue has been present in some form from the beginning on 89 fuel and I have found it goes away for the most part when using 92 or higher fuel. I had to change the pump out twice as the first one I bought was no good because it did not hold pressure , makes me wonder if this one is going the same route. I am planning on doing a fuel pressure check this weekend to see if anything shows up. I am looking for feedback on the possibility of changing to a higher volume pump as I have seen one on Morris 4x4 site.

lazyxj
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Joined: April 28th, 2017, 10:24 pm
Stroker Displacement: 4.6
Vehicle Year: 2001
Vehicle Make: Jeep
Vehicle Model: XJ

Re: fuel pump question

Postby lazyxj » November 29th, 2017, 8:28 am

Have you checked the fuel pressure? It should be around 49-psi, all the time, especially while under acceleration.
https://www.harborfreight.com/fuel-inje ... 62623.html

If the pressure drop-off under full throttle, I would suspect he pump assembly is not pumping adequate fuel volume.
It could be cause by a weak pump, badly plugged filter or a defective pressure regulator .
Also check the fuel supply line, making sure sure it has not been bent or crushed.

LRSimons
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Vehicle Year: 1995
Vehicle Make: Jeep
Vehicle Model: XJ

Re: fuel pump question

Postby LRSimons » November 29th, 2017, 2:55 pm

Maybe I read something wrong, but as I understood your issue:

I'm confused as to how a underperforming fuel pump could not deliver enough fuel under medium load and medium revs while delivering plenty in open loop. When you say open loop, I'm assuming WOT conditions. Does it run properly then? Are the 13ish AFRs throughout the rev range? If they are stable throughout there's no way it could be the fuel pump.


How are you measuring the AFR?

Fuel pressure check is a good idea regardless.


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