XJ40 ( XJ81 ) 1986 - 1994

Fuel pressure issues?

Old 05-02-2019, 09:41 AM
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Join Date: Mar 2018
Location: murrieta ca
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Default Fuel pressure issues?

So my car will lose power and sounds to be backfiring in the intake area. My fuel pressure at idle is 35 PSI, and with the regulator vacuum removed it goes up to about 44 PSI.
However, when driving and putting the engine under load, the PSI drops at times to near 20 PSI. This drop seems to correspond with the backfiring and lack of power.

I haven't been able to find data related to what the PSI should be while the engine is under load. Could the drop in pressure be related to the backfiring and lack of power?

Old 05-02-2019, 11:20 AM
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Join Date: Jul 2013
Location: North Hollywood CA
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Sounds like it is starving for fuel under load should be higher not lower. You may have a weak pump or bad check valve in the module. Does the pressure hold after you cycle the pump on and off?


Here is a manual for the car. Beginning of chapter 4 will have all the values you are looking for. Best of luck.
The following 2 users liked this post by nunger1330:
Don B (05-04-2019), Lawrence (05-02-2019)
Old 05-02-2019, 10:28 PM
Thread Starter
Join Date: Mar 2018
Location: murrieta ca
Posts: 37
Received 4 Likes on 3 Posts

Thanks for responding. It was the pump. There was sand or rust particles and what looked like deteriorated fuel line pieces at the inlet,,, yes it made it pass the pump strainer!! And this pump is only 2 yrs old!!

Runs strong now...
The following 2 users liked this post by 91calijag:
Don B (05-04-2019), nunger1330 (05-03-2019)
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