Stumped

[conkeytonk]

I bought this excellent vehicle new in 2001 equipped with the 5.4L engine and the rather expensive tow package. With 59K on the odometer she has been trouble free until now. I mostly only drive it when towing the toys.

It started when she would not start after being driven until it cooled down. When she runs she purrs perfectly. Then the engine began shutting down while driving and now won’t start at all.

I replaced the IAC and checked the operation of the inertia switch (good, I even bypassed it once). All fluids are fine and she was not overheating. My OBD II did not detect any trouble codes from the computer so I am stumped.

Can any of you experts out there advise me where to start troubleshooting? I promise to be a loyal member of this forum as they have helped me greatly with my flock of vehicles and I enjoy helping others when I can.

 

[outkast]

the start would be to figure out what is missing, fuel, or spark. First, turn the key on, you should hear the pump run near the left rear tire...a slight humm is what your looking for.

next, see if you can spray some starting fluid in the air intake. If it starts, then you are missing fuel, if it doesn't then you are missing spark.

try that and report back...

 

[conkeytonk]

Thanks Outcast, I'll try and let you know. I have suspected the fuel. I should have also mentioned that I replaced the fuel pump relay but it did not help. Just a gut feeling though. I'll check spark too like you recommend.

 

[conkeytonk]

Okay, I have a feeling this one is going to be tough to diagnose. There is a hum from the fuel pump when the ignition is turned on. Then I tried to start it and she fired right up and ran perfectly for some time. This is after replacing the IAC but she would not start immediately after replacing it a few days ago. So she is getting fuel and spark (at least some times).

I just can’t trust her until I find what is making her shut down all of a sudden. Any suggestions out there?

 

[conkeytonk]

After reading some of these posts and talking around I’m beginning to think the problem is the crankshaft angle sensor. I suppose the CAS would not send a trouble code to the computer when beginning to fail since I’m not picking any up. Since it dose not cost too much I think I’ll go ahead and replace. I heard it stated that it is a PITA to get to. Why? I would guess it is underneath the harmonic balancer which is probably both hard to get off and in a tight spot. Right?

 

[outkast]

I would most certainly think you would get a code even if it was starting to go bad. As soon as the parameters are not met, a code is thrown. With a fuel problem, you have a much higher chance of no CEL because there is not many sensors on the fuel side. Do a fuel pressure test and see what you get, also if you did not already, replace your fuel filter.

 

[outkast]

also, next time it wont start, try holding the gas pedal to the floor to see if it starts.

 

[conkeytonk]

Thanks Outkast, I was just about to purchase the CAS but will now invest in tools to measure the fuel pressure instead. As I said earlier, the OBD II does not pull any codes. I’ve checked many times. I need a fuel pressure gauge in my chest anyway as I have what I suspect is a fuel problem on one of my other project cars. What sort of device would you recommend I purchase to measure the fuel pressure?

And is it possible for the fuel pump to work intermittently ‘cause that would certainly explain my problem.

I have tried holding the pedal to the metal when she would not start and guess what? It still wouldn’t start.

Man, spring comes early here in Florida so I need to get this beast back on the road dependably soon so I can haul the boat to the gulf!

 

[outkast]

the reason I mentioned flooring it is because that puts it in clear flood mode. Since that didnt work, it rules out ofer fueling or flooding.

Usually, a fuel pump either works or it doesn't...usually. I am newish to these trucks, so hopefully someone with more technical experiance chimes in, but the fuel pump should just pump its a$$ off. A fuel filter could intermitantly clog causing a no start, or the fuel pressure reg, could be malfunctioning. Your symptons are remininsent of old school vaporlocking, which could be caused by low fuel pressure.

any fuel pressure gauge will be good. if you can find one with a long enough hose to see it while you drive (provided you can stick it somewhere and get the hood closed) would be better.

you may also want to invest in a shop manual for your truck, about 30$ from autozoo or whatever. It should list inside what your idle pressure should be.

 

[conkeytonk]

Okay, thanks once again Outkast. I meant to mention that I replaced the fuel filter about 10K miles ago as regular maintenance but will do it again now.

I’ll go out and get both a pressure gauge and manual this weekend and begin troubleshooting. I’m a fan of manuals and have one for my other three cars (and boat motor) but the Expy has been so dependable up until now that I have neglected to purchase one.

I’ll report back when I find something and thanks to this forum for anything it may do. I’ll keep an eye on the posts going forward and help where I can.