Long cranking when engine is warm (M20)

[Dan in NZ]

Whenever I try to restart the engine after it's been off after short time and already warmed up, it cranks for ages before starting. Starter runs for about 2-4 seconds before I have to tap the gas to make it start. When cold, the engine starts instantly with no gas. Could it be a thermo-time switch or something, that could also explain high gas usage??

[john 1989 525i]

Whenever I try to restart the engine after it's been off after short time and already warmed up, it cranks for ages before starting. Starter runs for about 2-4 seconds before I have to tap the gas to make it start. When cold, the engine starts instantly with no gas. Could it be a thermo-time switch or something, that could also explain high gas usage??
I was wondering if it might be the fuel pressure regulator.

[Dan in NZ]

I was wondering if it might be the fuel pressure regulator.

Hopefully someone can shed some light... It's kind of embarassing to get in your car, start it, then have it crank for ages and having to pump the gas.

[ryan roopnarine]

if you suddenly have higher gas usage (decreased k/litre if i understand you correctly) and holding the pedal down, it sounds like you have a leaking fuel injector(s). i'd sniff the exhaust when its running and see if it smells of "lawnmower".

ps.....this link might be helpful
http://minimopar.knizefamily.net/fuelsystem.html
though it doesn't specifically deal with bmws, it might be helpful.

if you were in the US, you could go to autozone and rent a vacuum pump and test the FPR for vacuum....but as you aren't, that isn't helpful. perhaps you have a tool loan place you could use there.



Whenever I try to restart the engine after it's been off after short time and already warmed up, it cranks for ages before starting. Starter runs for about 2-4 seconds before I have to tap the gas to make it start. When cold, the engine starts instantly with no gas. Could it be a thermo-time switch or something, that could also explain high gas usage??

[gale]

Could also be the check valve in the fuel pump doesn't seal completely & lets the pressure bleed down, leading to a vaporlock-like condition in the fuel rail, taking that much longer to fill up & purge itself when you go to start it again.

It probably behaves properly when cold when the vapor has recondensed to liquid. There is a simple fix for this, I think originally for the e38 m60, is an external check valve that splices into the fuel line near the filter, p/n 16 14 9 068 988, about $5 US.

The leaky injector theory that Ryan suggested could also cause the same vaporlock behaviour.

[Oleg©]

M20 here too 1989 263,000

new injectors, new fuel pump and long cranking times exactly as you describe
my theory is moisture condensation inside the rotor cap which may be caused by bad gasket or a tiny crack, no spark no engine start;
this condensation can occur only when the engine warm and started to cool off just a little bit temperature gradient and there it goes; before and after this moment this moisture is gone...


have you ever replaced the idle control valve or AFM?

[Tiger]

Definitely the Fuel Pump Checkvalve... the first thing I would change. Get the E39 checkvalve kit and install it on fuel hose.

[john 1989 525i]

Could also be the check valve in the fuel pump doesn't seal completely & lets the pressure bleed down, leading to a vaporlock-like condition in the fuel rail, taking that much longer to fill up & purge itself when you go to start it again.

It probably behaves properly when cold when the vapor has recondensed to liquid. There is a simple fix for this, I think originally for the e38 m60, is an external check valve that splices into the fuel line near the filter, p/n 16 14 9 068 988, about $5 US.

The leaky injector theory that Ryan suggested could also cause the same vaporlock behaviour.

so I`m sure you`ve nailed it.Thanks for the quick cheap fix.

[henryw525i]

1989 M20 525i Manual

I have had this problem for 3 years. My engine has been completly rebuilt new ICV and MAF completly tested.

And yep same symptoms. If the car has been sitting for a day and is dead cold it will fire INSTANTLY. But if its been left for anytime less than this it takes ages to crank. And yes my car is a lovely car in every way but it looks like a POS when it takes ages to crank:( When it cranks you can tell its getting closer and closer to firing coz the sound changes...then vrooom shes off. Its also strange becase I have no problems with power up the top of the rev range.

Symptoms I had with the car have been really screwed up stumbling acceleration. And strangely enough when i replaced the fuel lines in the engine bay the problem went away for 9months. Then it came back again..... Then I got the engine rebuilt and *touch wood* its gone away again. Therefore I figure it MUST have something to do with the fuel system i would think.

Anyway its done 210,000kms and has never had the fuel pump replaced...so I am going to get one from the dealer this week and put it in. I am going to do this becase even if its not the problem...its about the time fuel pumps die and I would rather replace it before it dies on me when I am miles from no where.


The idea of some problem with the rotor and spark system has crossed my mind and if the new fuel pump doesnt work that will be my next port of call. I dont understand how it could be the injectors when it fires instantly when its cold....it would be the otherway around if you had leaking injectors becase they would have to be leaking BADLY if it got the cylnder flooded if you only have the car off for 2mins....

anyway i'll post up what happens with the new fuel pump

-henry

[henryw525i]

Definitely the Fuel Pump Checkvalve... the first thing I would change. Get the E39 checkvalve kit and install it on fuel hose.

Your still going to have the problem with the existing fuel pump check valve arnt you?....so how does this new check valve fix the problem if the problem is started already up the line on the existing fuel pump?


pardon my ignorance? it sounds like a FANTASTIC idea if it works! :)

[Tiger]

E39 checkvalve is way cheaper way to fix it... Our E34 checkvalve is inside the fuel pump.... where E39 is outside the fuel pump but next to the fuel pump. The critical heat area is above the engine where you can create vapor lock.

So with the checkvalve by the fuel pump... you actually fixed the problem in a much easier way... 15 minutes job compared to 2 hour job.