Random starting problem - fuel related

[5Toes]

Hello all.

So my car starts fine nearly evertime. 2nd or 3rd crank usually. The revs really jump up though when it is started, to about 1600/1700 or so.

Either way, sometimes my car has an intermittent starting problem. It only happens after car has been running.

What happens is that the car will crank and crank and crank, with no signs of starting. To get the damn m20 to start I actually have to push the throttle to the floor and crank. It then starts up 3rd crank or so and IDLES FINE.

The issue is not a big deal, but it just sort of bothers me. I believe it is a fuel issue, sure sounds like one to me.

I have replaced the fuel filter, just an fyi

Any ideas?

[matt0300]

Cps going bad maybe. That's the first place id look.

[5Toes]

Cps?

[bernzpeed]

tap the fuel sender with your fist, underneath the rear passenger seats.

that happened to me then chitty banged on the sender with his fist and starts right up. every time my engine dies i do that and it starts right up. but i've replaced it since then.

[5Toes]

CPS... duh crank position sensor. Alrighty. Thanks Bernzspeed, Ill try it.

Whats your real name by the way?

[Sagaris]

I have read that some 7-series cars had issues with the check valve in the fuel pump going bad for which the cheap fix is to install an inline check valve BMW part # 16 14 9 068 988, rather than the whole pump. It is supposed to keep fuel from draining back into the tank and creating air pockets in the fuel lines. I bought one because my car had 3 or 4 long-crank episodes that started the week after I pulled it out of the garage from its winter hibernation. I didn't end up installing it because the problem cleared up on its own. This may not be your problem, it may not have been mine, but it is a cheap and easy way to rule out a possible bad check valve.

I agree with the crank position sensor suggestion, you should also check the toothed wheel on the crank pulley to make sure it isn't wobbling out of range of the sensor. If you want to do a little more diagnostic work, be ready with a spark plug socket when it is doing the no-start condition, pull a plug, ground it to the car (rest it on a good conductive surface) and check for spark. No spark would indicate a bad crank position sensor or point you in the right direction as to diagnosing other spark related issues rather than fueling issues.

I agree with the idea of tapping the fuel pump under the rear seat cushion. For diagnostic purposes you could try listening to the pump with the cushion off to see if it is running while trying to crank. I have a very hard time hearing the fuel pump in my car. If it was noisy like a Ford fuel pump then it would be incredibly easy :P

Another thing to consider would be leaky fuel injectors which would explain why you have to hold the throttle open while starting the car.

It is never a bad idea to check the idle switch on the throttle position sensor to make sure the ECU is reading the idle maps instead of trying to figure out a part throttle map for 300-500 rpm

[jlevie]

The "fix" of holding the throttle all the way open sounds like the engine could be flooding. Which in turn could be caused by leaking injectors.

[5Toes]

^ Levie. I never touch the throttle when cranking. After car has been sitting for Id say over 6 hours, it starts up fine. Just turn key and go.

If I turn the key and it cranks, and cranks with nothing. I stop THEN put the pedal on the floor and crank.

It cant possibly be flooding if I just crank without foot on throttle.

[5Toes]

I have read that some 7-series cars had issues with the check valve in the fuel pump going bad for which the cheap fix is to install an inline check valve BMW part # 16 14 9 068 988, rather than the whole pump. It is supposed to keep fuel from draining back into the tank and creating air pockets in the fuel lines. I bought one because my car had 3 or 4 long-crank episodes that started the week after I pulled it out of the garage from its winter hibernation. I didn't end up installing it because the problem cleared up on its own. This may not be your problem, it may not have been mine, but it is a cheap and easy way to rule out a possible bad check valve.

I agree with the crank position sensor suggestion, you should also check the toothed wheel on the crank pulley to make sure it isn't wobbling out of range of the sensor. If you want to do a little more diagnostic work, be ready with a spark plug socket when it is doing the no-start condition, pull a plug, ground it to the car (rest it on a good conductive surface) and check for spark. No spark would indicate a bad crank position sensor or point you in the right direction as to diagnosing other spark related issues rather than fueling issues.

I agree with the idea of tapping the fuel pump under the rear seat cushion. For diagnostic purposes you could try listening to the pump with the cushion off to see if it is running while trying to crank. I have a very hard time hearing the fuel pump in my car. If it was noisy like a Ford fuel pump then it would be incredibly easy :P

Another thing to consider would be leaky fuel injectors which would explain why you have to hold the throttle open while starting the car.

It is never a bad idea to check the idle switch on the throttle position sensor to make sure the ECU is reading the idle maps instead of trying to figure out a part throttle map for 300-500 rpm

Yeah I have a very hard time hearing my fuel pump. That was my first thought of the cause.

Spark plug wise, I dont see why I would not be getting spark. Or maybe my plugs are weak? Im doing plugs... possibly today. Ill take pics of the ones I pull and label them. Ill be going with NGK plugs. And Oreilly has a rebate on them now... Bosch too. Hmm.

CPS could be causing problem because it cant read the crank's position? Thats weird though, that after car warms up it does that.

Ill replace spark plugs, and report back. But it may take a few days for me get this "condition" again.

Off to Oreillys

[5Toes]

NGK ZGR5A's ordered from Oreilly. Yippee

[Sagaris]

O O O O Reillyyyyy :blowup:

[5Toes]

I pulled my #2 plug. Or #5. Second from the front on the engine.

It was SHOT. Def. need new ones.

[jlevie]

^ Levie. I never touch the throttle when cranking. After car has been sitting for Id say over 6 hours, it starts up fine. Just turn key and go.

If I turn the key and it cranks, and cranks with nothing. I stop THEN put the pedal on the floor and crank.

It cant possibly be flooding if I just crank without foot on throttle.

It can be flooded if the injectors are leaking. When the car sits those leaks flood the engine. If it sits long enough most of fuel will evaporate and/or drain past the rings. But on a hot start there can be enough fuel in the cylinders to require a wide open throttle to clear.

[blocke]

It can be flooded if the injectors are leaking. When the car sits those leaks flood the engine. If it sits long enough most of fuel will evaporate and/or drain past the rings. But on a hot start there can be enough fuel in the cylinders to require a wide open throttle to clear.

I'm experiencing a very similar issue, and I've also suspected the injectors. Thinking along those lines, would a leaky or sticking injector also cause horrible mileage? I have noticed that my gas mileage has gone down the shitter, and I do all highway, 100 miles a day.
I noticed it right after getting a new cat installed, so I wasn't sure if it might be the cat, or maybe the injectors.

[jlevie]

I'm experiencing a very similar issue, and I've also suspected the injectors. Thinking along those lines, would a leaky or sticking injector also cause horrible mileage? I have noticed that my gas mileage has gone down the shitter, and I do all highway, 100 miles a day.
I noticed it right after getting a new cat installed, so I wasn't sure if it might be the cat, or maybe the injectors.

Unless undersized, a new catalytic converter would improve fuel mileage as it would have less restriction on the exhaust flow.

Leaking or dirty injectors will decrease gas mileage. But there are other possible causes. Like intake leaks, incorrect rail pressure, a bad ECT, a bad AFM, bad ignition wires/plugs, misadjusted valves, a cold running engine, or an aged O2 sensor.