Need advice I’ve been having misfire codes such as PO304 and PO 3000 and P1316. Car runs and drives but Has a hard start on cold start and even when the engine is hot. The goes into restricted performance and is cutting power/ Hard hesitation at wide-open throttle. As soon as I clear the codes the car seems to run better then after about 2030 minutes car kicks into restricted performance with the same code.

Today I decided to rent out a fuel pressure tester and a compression tester. I did the fuel pressure test and for some reason the fuel Pressure was at zero it wasn’t reading at all, at first I thought I didn’t have it hooked up correctly but it was.

at the moment I am very confused it might be that the fuel pressure is so low it can’t be read on the gauge itself. I might have a stuck open injector we can fuel in this old head, but I don’t know because I think I will be smelling fuel or smoke coming at tail pipe or much worse idk

Also I know the car has two fuel pumps can one of them be bad ?
I’m
would anybody be able to assist me and guide me the right direction

 

If the car starts then you have some sort of fuel pressure. At the back of the fuel rail on the right hand side is the schrader valve for checking fuel pressure. Try a different pressure tester or maybe try screwing it on further. The valve also may be stuck. Another classic test is to push in the valve and see if fuel shoots out (be careful not to start a fire or get it in your eyes). You can repeat that test after the car has sat overnight to see if the fuel rail is leaking pressure. If your fuel pressure is low, I would try changing the filter first before going crazy with the fuel pumps (they're a bit difficult to get at).

That's about the limits of my knowledge. When you get around to testing compression, inspect each of the spark plugs. Also try moving the spark plug and coil pack from cylinder 4 to a different cylinder and see if the code changes positions as well.

 

How did you check the fuel pressure - with the engine running or only at the ignition "on"?

 

I have replaced all 8 spark plugs and ignition coils twice with brand new. And tried depressing the valve and it shot a small amount fuel out no high pressure land there was no more pressure in the rail after that. This was with the car off btw.

I have a 98 xjr and the valve is on the driver side front btw

I also tested the fuel pressure gauge and it works on my other car. I will try again tomorrow thanks for the helpful response keep you posted

 

I tested with key in ignition in second position no pressure at all. But I will try again tomorrow

 

You are getting "some" fuel pressure, or the car would not start at all. Low fuel pressure could be caused
by a number of things. The indication that the fuel pump has been replaced (twice) would seem to indicate
this problem has surfaced before, There may be some sort of restriction or "kink" in the lines coming from
fuel pump. I would test the pump output first and go from there.

 

It "runs better" (actually, worse) because you've also cleared (unset) the OBD monitors (used for smog etc) and so the car is defaulting lots of things (and can't flag faults).

You could do with more clues. See which OBD monitors (if any) have not re-set (set again) when the code(s) flag.

Also, have a look at fuel trims (hot engine, parked, at idle & again at about 2500rpm).

BTW I'm guessing you mean P0304 & P0300

 

Yes and no...

The second pump only kicks in at higher power levels, so that can be dead & the car will run. If the primary pump is dead the car won't start.

Mine had a dead secondary pump when I got it & didn't trigger any codes that I remember but once I got the pumps replaced (it's 6hrs labour to get the tank out to do them so might as well do both) it went a lot quicker when pushed.

I diagnosed mine with a bit of wire. The relays for both fuel pumps are in the boot, if you bridge the right two contacts (I can't recall which, but they are normal 4-pin relays so easy to figure out) you'll hear the pumps run in the tank. I was actually looking for the cause of a hesitation that turned out to the be the MAF when I found the dead pump.

 

The # 1 fuel pump will run for 3 seconds only with key rotation

This initial fuel pressure should be trapped and held for days

It will come on again for the duration of your drive by seeing engine rotation at the CKPS , safety design

You can jumper the fuel pumps at the trunk relays between socket 3 ( power source ) to 5

This will eventually drain the battery with the keys in your pocket

Notice the control fuse # 16 / 10 amp left heelboard fuse box for both pumps

In order that this fuse to be powered the left heelboard fuse box relay must close

This is referred to as the 2nd ignition positive relay

If you place your finger on it it will click closed with key rotation , if it does click it can still have burnt power contacts inside the relay

For a one-person check put the key in the run position , remove the relay and it should click back open or relaxed , replace it and should click again closed

As a fuel pump is failing it will burn the power contacts inside the trunk fuel pump relay ( s ) and burn the sockets on the fuel pump motor connector

Always a good idea to refresh the trunk relays on pump motor replacement

 

This suggests that your Pump #2 is faulty as it is this pump that is activated for ~3 sec. at ignition "on" to prime the fuel system. Then, when you start cranking the engine, Pump #1 will run and continue providing fuel while the engine is running. At higher fuel demands, Pump #2 will join Pump #1 and run while the higher demand is present.

If Pump #2 is faulty, you will not have fuel pressure at ign. "on" and the engine will enter the "limp home" mode which limits the engine to, I think, 3000 rpm. As suggested, test each pump by jumping the pump relays and listening for the pump sound. You do not need to have the ignition "on" for this test.

 

There was something about if the car fails to start it will turn on the other pump in the starting sequence and call that one the primary fuel pump

I stole your relay pic and used it many times for others

 

Yes, during cranking, the Pump #1 is activated by the ECM and it is supposed to provide fuel for the engine start-up and running. If Pump #1 happens to be faulty (there will be no start), the ECM will switch to Pump #2 and run the engine on it but it will be in the "limp" mode.

 

Thanks all for all the helpful information really came in handy. I went ahead and jumped fuel pump number two with a wire. And heard no fuel pump. Looks like was running of the primary fuel pump the whole time. I replaced both fuel pumps and car runs much better then before. The car dose seem to crank for about 2 seconds when engine is hot, don’t know if that’s normal but issue seems to be some what resolved. Today my brother took the car on a test drive and restricted performance came on and the was hesitating again. When he came home I let the car cool down for awhile and disconnected the battery and reconnected. No check engine light after a hard test drive or hesitation at all. Could it be bad injectors from the faulty secondary fuel pump. It also might be computer might have been confused not sure.

Any form of advice would be great! Thanks