318is runs fine, then won't start when hot

[ras_austin]

I've got a '91 318is (M42 engine) that starts fine when cold; can be run for a little while, stopped, and restarted fine a few times. However, drive it for about a half-hour in the heat (Austin TX = 95 degrees), whether in traffic or on highway, and if you stop the engine and try to immediately restart the engine won't start. (It will half-fire a second or two like it's starving for gas, then immediately die).
Diagnosis so far: Fuel Pump relay, fuse block, all check ok. Voltage recorded at fuel pump. Haven't pulled the fuel pump, but this problem will happen at either full or empty, so didn't think fuel pump overheats (fuel pump is 1 year old). There is fuel pressure at fuel filter, but fuel pump doesn't run for a second when key is turned to "on" before starting (like it does when cold).

Is there a second fuel pump on the M42, or would a pressure regulator getting hot cause this? Remember, this car is running great before you turn the key off. Then nothing.

 

[Rukus]

maybe its vapor locking somehow.

 

[Lowen]

Does it actually turn over or no?

 

[ras_austin]

If by turn over, you mean the engine turns when the starter is engaged, yes. It might actually ignite on one or two cylynders then die.

Footnote: usually around 8-10 hours later (at night, when it's cooler) the car starts on the first try. But in between that interval, nada.

Thanks for the help!

 

[ras_austin]

one more thing: I have also checked the airflow meter and the only code the Motronic gave me was for the oxygen sensor.

About 6 months ago, I had a rough idling problem when cold, which was related to a cracked bellows between the airflow meter and the intake butterfly. Patched that up and she ran like a champ.

143K miles, btw.

 

[junglestylz]

Hey Lowen, could this be a thermo time switch problem¿

 

[Rukus]

A thermo time switch controls the cold start injector, which is understandably used for cold starts. What it does it tells the injector to either allow more fuel throught that ONE cold start injector or to not allow more fuel for cold starting. So whether this is working or not would not affect a thing.

If that thermo time switch was not working, it would only affect starts when the engine was cold, and not when it was warm.

i would try manually hooking the fuel pump up at the relay block.
If you don't know how to do this, ask Lowen, because i forget, and don't want to tell you the wrong thing. You said your afm was cracked at some time so what it could be is the switch in the afm that tells the pump to work or not, could not be functioning properly. Warped or cracked AFM's are due to backfiring.

 

[ras_austin]

I have jumpered the fuel relay (terminals 85 & 40 - if I remember right; 86 & 87 are the teminals that apply voltage to pull the relay shut, yes?) and that did not work. (Voltage did get all the way to the fuel pump)

Update: After getting the car towed & impounded b/c it died in a Sonic parking lot & the Sonic night manager was an a**hole, went to start it in impound lot with no luck. Got out of car, talked with the tow guy for about a minute, got back in car, for some reason I pumped the accelerator once & held clutch in, turned key and it started right up.

!@#$%^&*

 

[Lowen]

Well my first guess was that the starter of cylinoid was acting up when getting hot. With tighter tolerances as things heat up (including the slight compression increase), it's quite common to have higher compression motors have hot starting issues. But since you said it turns over, thast not it....

2nd guess was the fuel relay since you said your fuel pump is ok. But your last post exhausted that idea aswell....

A few other things;

Check your fuel relay when the car gets hot (it still may be this as it may be relative to only when the cars been running).

Check your main relay. When it dosn't start give it a tap (orange relay on the 318is) with the end of a screwdriver (or like). If than it starts you've narrowed it down to it being the main relay. For some reason I think that it may be this...but thats just a hunch.

Also check the breather tube from the intake manifold to the afm boot.

Any thought on it being ignition related....?

 

[ras_austin]

I thought about the ignition in the back of my mind during all this - but I haven't smelled gas when trying to start it (of course I haven't pulled the plugs to see if they were wet) - so I haven't gone down that path yet.

I also wasn't thinking ignition b/c it was running well before shutoff. But the main relay... that's a thought. If this one of the three on the firewall, (Fuel pump is in the middle) they all are getting pretty warm in there.

 

[dsobering47]

hey lowen......why did you get banned from all the other BMW forums.......

hmmm.......................

 

[ras_austin]

Problem solved. The fuel pump finally seized up. This was a replacement for the factory original, which had lasted 10 years. The aftermarket pump lasted 1 year 3 months. Is this typical?

Speaking of the original factory pump, I found some old pics I took of the OEM fuel pump when I replaced it last year.
Notice the burn marks around the terminals. Was this a ticking timebomb or what? Anybody else seen this kind of overheating?

Thanks for your help.

 

[Rukus]

the reason that a submersible pump DOES NOT ignite on fire, heat up etc., is becuase it is TYPICALLY submersed in fuel.
The fact that it is always in fuel, starves it from oxygen (crucial to combustion) and also is supposed to keep it from overheating. WHY this happenend to your pump is puzzling.