Fuel pump, FPR or something else?

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sprocket

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My '96 is occasionally starting hard and it is clear that it is not getting any fuel. Turning the key on and off a few times doesn't help. I can clearly hear the pump solenoid working. Tonight it wouldn't start at all for about six tries. Then all of the sudden it starts like nothing was ever wrong. It's not flooded and the RPM doesn't go up like it is clearing excess fuel. It just starts perfectly normal.

Once it's running, it runs fine. I might start it 6 times in a row with no issues and then it might act up the next three times.

I haven't checked the fuel pressure yet. I would think if it was the FPR the problem would be consistent. There is no rhyme or reason based on how long it sits either.

I'm guessing the fuel pump might be on its last legs.

Am I right or could it be something else?

Thanks for any help!
 
Define starting hard. As in nothing besides cranking or its tries and sputters.

Cam position sensor is responsible for injectors firing. Crank positing for spark and starting. The crank position sensor is a common issue. Sometimes unpluging it and pluggin it back in will cause the car to fire up on the next try.
 
unity said:
Define starting hard. As in nothing besides cranking or its tries and sputters.

Cam position sensor is responsible for injectors firing. Crank positing for spark and starting. The crank position sensor is a common issue. Sometimes unpluging it and pluggin it back in will cause the car to fire up on the next try.
Click to expand...

It does nothing but crank. No sputtering at all.
 
Like unity said good chance its a crank shaft position sensor.
Also the wire harness right there can go bad.
Both can be had on rock auto.
 
The fuel filter has been changed. Is there any tests I should do to rule out other things? It doesn't look like it is too big of a deal to change it once I slide the A/C pump out of the way. Hey, I put the engine in this car from the top so compared to that, anything is easy.
 
Spray it up good with electrical cleaner and move the connection wiring around a little and retry the start before you start ripping stuff apart.
 
Could be crank position sensor, fuel pressure, or any number of spark or fuel issues. Hard to diagnose over the web but give us updates and check the common problem areas and we can go from there.
 
It never stalls while running. I've cleaned the connector last year when I was under there for something else. It looks fine. I'll have more data this weekend.
 
chris2523 said:
this does not fit with a bad crank sensor in my experiences.
Click to expand...

I was going to ask why but now I went and read the symptoms of a failing crank sensor. It doesn't fit the symptoms. I will check fuel pressure and pull codes.
 
If pressure is good, then move onto cam sensor if you think crank sensor is fine. The cam sensor is only used on startup as far as I know. So if the cam sensor is problematic, it will not fire injectors and thus not start. But once started, a bad sensor is not an issue.
 
Fuel pressure key on, engine off is 35lbs and takes a few on/off turns of they key to build pressure. Perhaps that is because the fuel system depressurized when connecting to the schrader valve. With the engine running the fuel pressure is 32lbs. I tried two gauges with the same result. Revving the engine does not increase or decrease fuel pressure. There is no fuel present at the vacuum line to the FPR. Disconnecting the vacuum line to the FPR with the engine running results in the pressure increasing to 40lbs. The pressure bleeds down less than 5lbs in 10 minutes after the engine is turned off. After that, key on, engine off returns the pressure to about 35lbs.

So the fuel pump is weak and should be replaced. That being said, I can't see it causing the car to not start. Perhaps I should replace the cam sensor now and see if the starting issue goes away. I had no trouble starting the car today. I can then replace the fuel pump when I have the time to do it.

I know I can look it up, but what is the most popular pump and where can I find instructions on the easiest way to change it?
 
unity said:
If pressure is good, then move onto cam sensor if you think crank sensor is fine. The cam sensor is only used on startup as far as I know. So if the cam sensor is problematic, it will not fire injectors and thus not start. But once started, a bad sensor is not an issue.
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The cam sensor is not used on start up. The car will run without it, its used for fine tuning.
His problem is coming from the ckp sensor more than likely.
I guarantee if you unplugged the cmp sensor on a good running mark it will start.
 
slowmkviii said:
The cam sensor is not used on start up. The car will run without it, its used for fine tuning.
His problem is coming from the ckp sensor more than likely.
I guarantee if you unplugged the cmp sensor on a good running mark it will start.
Click to expand...

I agree, the crank sensor seems to cause the issue hence my original thought. But others seemed to think not. As far as I know the cam sensor is indeed used on startup to determine cam position. Either the tech book was wrong or its an OSBI versus II thing. I would love for someone to try it out though and see what happens, then we know for sure.
 
unity said:
I agree, the crank sensor seems to cause the issue hence my original thought. But others seemed to think not. As far as I know the cam sensor is indeed used on startup to determine cam position. Either the tech book was wrong or its an OSBI versus II thing. I would love for someone to try it out though and see what happens, then we know for sure.
Click to expand...
I have run an obd 1 car with out a cam sensor
But have not tried it on a obd 2 car
 
I cleaned the contacts on the crank sensor and the plug. They were dirty. I must have been remembering the D.A. when I said I had already cleaned them. I have had no starting issues in the last five or so starts.

I'm wondering if the 32lbs of fuel pressure at idle might be normal? I don't have enough hose to stick the gauge under the wipers while driving. I'm guessing the fuel pressure probably does get into range under load.
 
unity said:
I agree, the crank sensor seems to cause the issue hence my original thought. But others seemed to think not. As far as I know the cam sensor is indeed used on startup to determine cam position. Either the tech book was wrong or its an OSBI versus II thing. I would love for someone to try it out though and see what happens, then we know for sure.
Click to expand...

slowmkviii said:
I have run an obd 1 car with out a cam sensor
But have not tried it on a obd 2 car
Click to expand...

im gonna go try right now on a 93 and a 96. brb.

sprocket said:
I'm wondering if the 32lbs of fuel pressure at idle might be normal? I don't have enough hose to stick the gauge under the wipers while driving. I'm guessing the fuel pressure probably does get into range under load.
Click to expand...

32 psi at idle is normal. should be a little over 40 at full load, wot, no vacuum, etc.
 
i forgot the 97 was here too. so i added it to my test.
on each car, i unplugged the cam sensor and went to start the car.

all 3 cars started first try. and i observed no CELs on all 3 cars.

my conclusion is that the cam sensor is not used on startup.
 
The cam sensor is used when cranking to start to determine which stroke of the piston to inject fuel. If it is unplugged or fails, the PCM simply defaults to a 'guess' which is based off the crank sensor and it has a 50/50 shot of guessing right. If wrong, it fires the injectors on the wrong stroke of the piston and will not start. Once the engine is running, the cam sensor is basically ignored since the PCM has the proper sequence.
 
driller said:
The cam sensor is used when cranking to start to determine which stroke of the piston to inject fuel. If it is unplugged or fails, the PCM simply defaults to a 'guess' which is based off the crank sensor and it has a 50/50 shot of guessing right. If wrong, it fires the injectors on the wrong stroke of the piston and will not start. Once the engine is running, the cam sensor is basically ignored since the PCM has the proper sequence.
Click to expand...

well i unhooked the cam sensor on 3 cars, and got first try starts 3 times. and i did it several times on the 93. so am i just really lucky?

and why wont the engine start if the fuel injector is timed wrong? wont the fuel just sit in the intake for a little bit until the intake valve opens? or??? wasn't a problem with batch fire injection, they would launch a whole side at once.
 
Probably should've said "may" not start.

I'm just saying how it works... you can read into it what you want. LOL
 
Update: The Mark VIII will not start at all now. It is not getting fuel. If I spray starting fluid into the air intake it will start for a few seconds. I checked the fuse. I swapped relays. I checked the cutoff switch in the trunk. I depressed the schrader valve and there is no fuel pressure at the rail.

So, could the problem still be the crank sensor or is it for sure the fuel pump? Is there a way to confirm it is one or the other? Are there still other possibilities? It is at about 200,000 miles now.

Thanks for any help!
 
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