Hi all, our 1996 x300 4.0 has begun stalling out. It runs for several minutes then the engine dies. It restarts, then dies again after a few minutes. I want to determine if this is a fuel or ignition problem. When the ignition is switched on we can hear the fuel pump run, then stop when it reaches pressure. There are no error codes. It has a mechanical fuel pressure regulator that's original, so I thought I'd start by checking the fuel pressure. I can rent a test kit for this, but don't know if it'll have the proper fittings in the kit.
Has anybody had any experience with this that can pass along some advice?

Thanks!

Bobby

 

Sometimes just a bad tank of gas at the last fill can be the problem

You can also jumper the fuel pump relay to determine if the relay has a control issue

You can use a short heavy wire with blade type connector to make better contact in the relay base sockets being the forward most and aft most sockets of the 4 sockets in the base

The auto parts stores often have a toy box to assist you in building this jumper

 

Hi Bobby,
There are many posts which may relate better to the symptoms you are seeing.
When the car is running, do you notice any idle problems or rough running before the stall? This could help determine the cause.
You could be looking at chasing down an electrical fault, but here's a few potential failures to check for first.

Engine Coolant Temperature Sensor (caused mine to run for a while then rough before a stall)
Intake Air Temperature Sensor (could affect running, but maybe not stall)
Crankshaft Position Sensor (can cause poor running and idle)
Idle Air Control Valve (can cause poor idle and stall)
Coils & Spark Plugs (can cause poor running)
Fuel Pump & Pressure Regulator (can cause poor running or stall)

These seem to be the main problem areas I have experience of. Hope it helps.

 

You can add a blocked fuel filter
Bad TPS.

Start with the cheap and easy. Coolant Temp Sensor is about $20 and should take you less than 5 minutes to replace.

Next, the fuel filter. Probably original to the car, right? About $20 and an hour of your time.

Does it run better when the engine is cold? That would indicate that one of the sensors it ignores until it reaches operating temperature is bad. (that coolant temp sensor is not ignored, cold or hot, btw)

 

Thanks all, I'll be checking everything suggested. The fuel filter was replaced by me about 2 years ago when we replaced the injectors. However the old filter had thick sludge inside and so it's very possible it's clogged again. It's also possible water got in the tank. Pump relay and electrical are also in play. I thought id start with the fuel since I have had the filter out before and so I'm firmiliar with it. I only hesitate because whomever replaced it earlier closs threaded one end. I was moments away from cutting the steel line and putting on a new end when we got it tightened to where it no longer leaked (installing the new one). So I cringe at taking it out again. But I suppose replacing it and letting the pump empty the tank is the only way to eliminate clogged filter and water in gas from the list. I'll also try the water temperature sensor. As we eliminate them one by one we'll move on to the other suggestions.

Thanks all!

Bobby

 

Also, I wasn't present when the engine stallef, but my son did say it started to sputter first. By the time he pulled off the road it died. It restarted an hour later and stalled again after maybe 5 minutes.

Quick questions. We recently replaced the thermostat. Could that be causing it? Would an overtemp shut down the engine?

Thanks

 

The spluttering before it dies is a good clue, and likely points at fuel, as you have already surmised. There would be no harm and minimal cost in replacing the filter, and it is likely that any thread damage will be on the softer filter rather than the pipe fitting, so a new filter should solve. Remember the little O rings on the pipe ends!
I wouldnt think the thermostat would be contributing to the problem, and an overheat would manifest itself pretty clearly. I do not believe that there is any overtemp protection as such.

 

Thank you for the reply. I'm ordering a new filter now so we'll have it in hand Monday (my next day off). To empty the tank I guess we'll need to jumper the fuel pump relay? If I remember correctly the pump will automatocally shut off when there is no pressure building up?

Thanks.

Bobby

 

just siphon it there’s nothing stopping you

 

Thanks all. We pulled the filter and while it had some dirt it wasn't bad. Nowhere near what i pulled out 2 years ago. We installed the new filter but the engine still sputters. Tonight we rented a fuel pressure test kit. Unfortunayely it dosen't have the proper fittings, so we're going shopping for adapters tomorrow. Does anybody know what the proper pressure should be? And would it change when the car is moving?

Thanks!

Bobby

 

Ooh….where are you adding the test port? I tried putting together a Frankenstein assembly to add a schrader valve, but it leaked….badly. I’d recommend cutting that return hose and sticking something in there with barbs.

I recall a fuel pressure of 40psi, but please check me on that. I think that’s what the fuel pressure regulator is set at.

 

Thank You Vee, yeah, my first version of an adapter failed and there was fuel spraying out of the input of the pressure regulator. We had an old rusty fuel rail laying around so I ended up cutting off the return pipe from that to create a good fitting back to the regulator. I don't like destroying even old used parts, but we needed an answer. It worked well though.




The pressure hovered between 38-40 lbs when running, but jumped near 480 when we opened the throttle. It this normal? It's here we also noticed an issue that appears to be associated with our overall problem. If I opened the throttle slowly, all was good. If I opened it quickly, the engine hesitated and shook for a brief moment before catching up. No new error codes logged. Video clip below.

Opening the throttle with fuel pressure gauge nearby.

Any ideas what might be causing this?

Thanks,

Bobby

 

I fixed a vacuum leak this weekend and noticed I have a similar response on mine. Very slight hesitation before revving on quick bursts and steady revs on steady bursts.
I am thinking Fuel Pressure Regulator or Fuel Pump.
I am assuming that since you see steady pressure without revving the engine, that it could be the regulator. Although I did read on other posts that the pressure should be 43si at the regulator.
Can anyone confirm or advise?

 

My understanding of how the fuel supply is supposed to work is that the pump is constantly running when the engine is running, producing sufficient fuel flow to sustain the engine at maximum revs. The ECU controls the injector timing and duration to meet the needs of the engine having regard to throttle position, load etc etc. . When the engine is not at full throttle, excess fuel is being supplied by the pump which builds pressure in the fuel rail until the fuel pressure regulator opens to release the excess pressure into the fuel return line. In a perfect world, the pressure in the rail would be absolutely steady, but given that the fuel pressure regulator is essentially just a diaphragm and a spring, it will tend to fluctuate somewhat within a range particularly when engine demand is changing rapidly and markedly, such as when it is being revved at idle. You will see that there is a vacuum connection to the regulator which helps to dampen such fluctuations, and which may explain why fixing a vacuum leak made a difference.( By the way, if your car is an auto, I would avoid revving beyond 2000rpm in neutral).
My take on your results is that they look ok. The hesitation you show doesnt seem excessive given the throttle was snapped open so quickly.

 

Thanks for the info countyjag. It's good to know to expect that slight fluster before stomping the pedal. This is good, since I rarely push things from a standing start.
Going back to Bobby's spluttering issue, I guess that confirms his fuel pressure is roughly where it should be.
So that leaves remaining usual suspects
Coolant Temperature Sensor
Idle Air Control Valve
Coils
Crankshaft Position Sensor

 

Thanks all. I'm starting to take an accounting of the possible sensors. Starting with the lowest cost first. Regarding the coolant temp sensor, I should be looking at the sensor on the thermostat housing with the two prong connector, correct? The single prong connector is for the gauge, is that correct? I measured the temperature with an IR thermometer and the thermostat housing hovers around 180° F when running.

Bobby

 

HI Bobby,
That's the one just by the thermostat with the 2-pin connector.
If you have a multimeter you can check the resistance of the current sensor and see if it is in the right ball park.
You could also check the live data with an OBD2 reader.

Here's the location and expected resistance/temperature readings

 

The IR thermometer reading is almost irrelevant. What is relevant is what the sensor is telling the ECU.

A LTFT reading would be great.

I can't tell what is causing the stall? At idle only? While driving only? Both? Something else? The fact that this happens whether the engine is cold or warm narrows it down to (1) MAF (2) TPS (3) Coolant Temp Sensor (4) Crankshaft Position Sensor and (5) the always possible, crappy coils.

 

History would suggest that unless it has been replaced recently, the crankshaft position sensor is always a good place to start with an X300.

 

Hi all. We've gotten a bit more information regarding this issue. The stalling doesn't happen until the engine heats up. For the first 5 minutes or so when cold the engine runs and accelerates without any issues. After that we notice a slight sputter, then after 10 minutes of run time it sputters a lot. We realized that this then is the same issue as when we first got the car (car would stall after 20 minutes of running), and replacing the coils fixed it at that time. So I've ordered new coils and plugs (the Champion plugs mentioned so often here). We've also ordered and received a new crank shaft position sensor, 4 new o2 sensors and an idle air flow sensor (think that's what it's called. Mounted on the throttle body). I ordered a new coolant temperature sensor, but it was the wrong one. However the readings on the existing sensor (purchased last year) seem to be within range. 1743 ohms when cold (90 degrees F, 280 ohms when at 180 degrees F). Because of the cost we're holding off on a new MAFS and TPS. I did manage to get the TPS IDLE voltage at 0.54VDC, but did not yet get a full open throttle voltage. We're hoping the new coils do the trick though. If not, once we have all the other new sensors in place maybe we can get some better information from the ECU on what's going on. Also, about 18 months ago my son hit a speed bump too quick and it destroyed the exhaust piping, so we had to have it replaced. The upside to this is that it came with two new forward cats.

Right now the starter motor quit, so all this is on hold till that's completed.

Thanks everybody for the help!!

Bobby