Hey guys, Im having trouble with my xjr not restarting after about 15 mins of being parked. Runs fine but If i want to restart it I have to unplug the fuel pump relays and them plug them back in as soon as it starts. Temp sensor is accurate, maf measures 5 g/s at idle and rail pressure is about 50psi. pulled all the plugs to check for a leaky injector and no standing fluid. I did find cylinders 1,2,5 and 8 to have fairly clean piston head while the others were fairly carboned up. Also car is constantly starting at 10 advance and doesn't seem to change for temp. This is kind of a weird one so I thought I would jump on before i started diving deap. Thanks in advance.

 

Sounds as if you are suffering from "heat soak". Most likely the auxiliary water pump is not operating. Try turning the the key to the ON position and with the hood open you should hear the pump running. If it is then time to troubleshoot. First unplug and using a multi-meter you have voltage going to the pump. If you have voltage and the pump isn't running then it is time for a new one.

 

That was one of my first thoughts. However I have monitored intake temps at around 70* while its no starting. I know the pump is on its way out because it doesn't sound good. I would imagine it bases fuel on intake vs coolant temp. Seems to start very rich when it does start. My second thought is that the ecm doesn't wanna learn a warm start. Ive tried 2 hard resets with no change.

 

Watch OBD values very closely and compare:
1. when it's good
2. when it's bad

with luck you'll see what's wrong.

 

The intake temperature reading is sent to the ECM and is probably correct at 70 degrees. The problem is the AIT air inlet temperature is upstream of the supercharger and isn't reading the temperature of the inlet air in the supercharger. The ECM sees 70 degrees and fuels appropriately, "heat soak" has the supercharger at a considerably higher temp and the result is the ECM is actually over fueling for the temp seen in the supercharger. Pulling the pump relays and cranking allows evacuation of the excess fuel and initial restoration of the relays allows it to start before over fueling kicks in again.

 

That makes sense.I would imagine the supercharger temp is pass side in the back of the manifold. I wonder if I may also have a bad sensor. I cant seem to find a reading for it on torque. Either way ill start hunting down a Mercedes aux pump.

 

Replaced the worn out pump with the bosch high flow supercharger pump. No change. Actually it failed to start this morning at about 65*. Had to hold my foot to the floor. Kind of lost now. My guess is its fuel related. I get a nice puff of black smoke when it does fire.

 

You said that your fuel rail pressure is about 50 psi which is a bit high and may cause rich condition. While the engine is running, the correct fuel pressures should be ~38 psi and should increase to ~44 psi when the vacuum hose to the pressure regulator disconnected. The pressure regulator vacuum hose is connected to the vacuum port on the supercharger, just below the coolant filler plug. Check whether the vacuum hose has, perhaps, detached from the port. If it is connected, you can use this connection point to test the fuel pressure when connected and when disconnected.

Another thing that can cause rich running, i.e. difficult start when hot, is a faulty coolant temperature sensor or its connector so have a look at this as well. The resistance values of the CPS should be as follows:

 

The car has an after market fuel pressure regulator, so i dialed that in. Thanks for the temp resistance chart. Its reading accurate through the obd but ill double check it. Im wondering if perhaps my charge intake temp sensor is faulty. I cant seem to find a pid for it on sdd or through torque. Any ideas? My only other thought is idle control through the throttle body is faulty? I notice that after I pull the fuel pump relays and get the car started, once I put the primary back in the car bogs for a second, then runs fine.

 

A couple other things to mention is that the car has a next gen Eaton out of the x350 along with a smaller pulley and bosch upgraded supercharger cooling pump. Also im told 340lph pumps from PO.This issue is a new development. The car runs fine with the exception of pinging under hard throttle around 3300 rpm which I attribute to needing either a tune or tunable MAF.

 

Set the fuel pressure to 38 at idle. Seems to be getting worse. After a cold start today it was hunting for idle until it finally evened out.

 

Anyone know what the bleed down time for the fuel rail should be?

 

What do you refer to bleed time? You can bleed the system by pushing in the schrader valve at the front left side of the engine on the fuel rail. Or unplug both fuel pump relays and crank the engine for a few seconds.

I would think this is a fuel-related issue. Maybe your primary pump is going out. The second pump supplies more fuel at around 3000 rpm. My hypothesis is that if it's not getting enough fuel at that engine speed, then the energy absorbed by the mixture from compression goes into heating a leaner mixture (energy required to heat up air is less than the energy require to heat up gasoline), and thus the in-cylinder temperature increases and causes pre-ignition.

What do your fuel trims look like at idle, when cruising, under light acceleration, under hard acceleration? What is the degree of timing advance under those conditions as well?

Try putting gas from either Chevron or Shell, as well.

 

I had a Porsche 944 that would do this. It turned out the ground strap from the engine to the body was corroding from the inside out and wasn't making a good connection. I replaced the ground strap and no more issues.

 

I think I may be onto it. It was mentioned earlier. I had it running today and disconnected the cam sensor which had no affect. Perhaps I have a bad cam sensor. Problem is I dont have a pid through sdd to find out for sure. Should it show resistance across the pins?

 

Yes, it should show about 2 Kohm. Otherwise, the engine will run without the Cam Sensor because the ECU will, as a fail-over, use the signal from the Crank Sensor and calculate the cam position from it. I know that, if the Cam Sensor is disconnected or bad, the engine will still start (if you keep the key in the "ignition on" position for some 40 sec. before cranking) and will run fine but I do not know whether, if you disconnect the Cam Sensor while the engine is running, the engine continues running fine because of the mentioned fail-over feature or because the sensor was bad to start with. If you can start the engine easily, i.e. without having to wait in the "ignition on" position, then your Cam Sensor is probably good. Anyway, test it with a multimeter.

 

340 lph pumps !? (each I guess). Fuel pumps rarely have more than 200 lph and that is for more special applications (like racing engines). The standard X308 pump has probably no more than some 100 lph. This may actually be your problem - at 340 lph, the pump may be overwhelming the FPR which then can no longer control the fuel pressure. And then, when the second pump comes on (hard acceleration), another 340 lph are added which may be the reason for your pinging (way too rich mixture). There is no point in using a very high flow fuel pump when the engine never takes so much. It will just force the FPR to send a lot of fuel into the return line back to the tank. Since the return line is rather long and fairly small diameter, plus it has an inline check valve, at too high flow it can cause serious back-pressure messing up the FPR operation.

 

The ignition for 40 seconds trick didnt really make a different, plus I have a cam sensor fault after unplugging it which doesn't bode well for a bad cam sensor. I can feel it; This is going to be something stupid and simple which is going to **** me off. The rail pressure is at 38 so im good there. Even with the overkill pumps 38lbs is 38lbs. Also the car has been starting fine for about a year with these pumps. My gut tells me the pcm isnt learning a warm start or isn't seeing a warm start signal but I don't see how that could be the case. I might throw some plugs at it, maybe they are fouled?

 

When you mentioned in the OP that it won't start, what do you mean? Does it not crank over? Does it crank but not fully start?

 

It cranks but does not fully start. The exceptions are that sometime if I pin the throttle it will eventually rumble to life very rich, or if I crank it, then remove both fuel pump relays it will fire right up and run long enough for me to reinstall the relays and then runs just fine. On cold starts it will usually fire right up and sometimes if I stop and restart it will fire back up.