P36 BMW Diesel hot start..

shaunm41 · May 17, 2009

I have a p38 with the 2.5 BMW engine, 92000 miles, currently having gearbox repaired.. But Ive been thinking if im spending all this money having it put right it may as well be totally right..

Its had on when i bought it one of the hot start fix things fitted (just looks like a small black box with wires going in and out), not sure what it does but i was told it helps it start when hot.. It seemed ok if you let the pre heat work even when hot but before it went in for the gearbox doing it just seemed to crank over for ages and ages before it would even try fire up..

Any ideas that could sort this if i took that black box off (as im guessing if it was ment to have that it would be fitted as standard right?)

Im a HGV driver and I had that problem with my truck, only it cranked over for ages when cold before it would fire up when hot fine.. Problem sorted with a set of new injectors.. but would that benefit my Range rover?

Thanks
Shaun

gavbriggs · May 17, 2009

i'm not sure its the same kinda problem as yer truck, i think its a fuel issue ecu issue as opposed to poor condition of injectors but new injectors wont hurt!

Datatek · May 17, 2009

shaunm41 said:
I have a p38 with the 2.5 BMW engine, 92000 miles, currently having gearbox repaired.. But Ive been thinking if im spending all this money having it put right it may as well be totally right..

Its had on when i bought it one of the hot start fix things fitted (just looks like a small black box with wires going in and out), not sure what it does but i was told it helps it start when hot.. It seemed ok if you let the pre heat work even when hot but before it went in for the gearbox doing it just seemed to crank over for ages and ages before it would even try fire up..

Any ideas that could sort this if i took that black box off (as im guessing if it was ment to have that it would be fitted as standard right?)

Im a HGV driver and I had that problem with my truck, only it cranked over for ages when cold before it would fire up when hot fine.. Problem sorted with a set of new injectors.. but would that benefit my Range rover?

Thanks
Shaun

Unlikely to be injectors, more likely to be glowplugs, glowplug relay or injector leakoff pipes leaking or finally fuel flowing back to the tank, look for air bubbles in the clear plastic tube from the fuel filter

Best leave the hot start fix alone as you might just confuse the issue by introducing another fault!

gavbriggs · May 17, 2009

i'm sure its a common problem on these engines, not sure of the fix tho!!

shaunm41 · May 17, 2009

ummm.. I think it might be a bit of trial and error then.. the hot start fix seemed ok till i jet washed the engine.. haha.. its a bit annoying if you stall at lights though as you have to wait till pre heat light goes off then give a further 3 seconds, otherwise you get endless cranking...

gavbriggs · May 17, 2009

have you tried the preheat twice in a row?

really, diesel should start once hot without glow plugs shouldnt it???

shaunm41 · May 17, 2009

Yeah I tried that, but i agree with what you said about a diesel starting without glow plugs when hot, I thought that the glow plugs only heated the diesel so it would start from cold, all other diesels I know fire up right away on the 1st turn when hot with no preheat..

gavbriggs · May 17, 2009

all the old diesels used to run forever and you had to stall em to stop the engine!

eightinavee · May 17, 2009

The hot start fix kit is fitted to cover up for a worn injector pump,when they wear they dont supply a sufficent start quantity because of internal leakage.The balck box links in a 2.5k ohm resistor in place of the coolant temp sensor every time you switch on.This puts the glow plugs on and gives more pump advance - the combination should be enough to start the engine.When the coolant temp goes over 60c the engine ecu does not put the glows on and uses less advance.
So if your engine will start from cold there are 2 probabilities,first the hot start kit is not working properly,second the pump is so shot there still is not enough fuel to fire it up.Try squirting a cold hose pipe onto the injector pump for 5 mins when the engine is hot.If it fires up quickly you know the pump is worn.

shaunm41 · May 17, 2009

eightinavee said:
The hot start fix kit is fitted to cover up for a worn injector pump,when they wear they dont supply a sufficent start quantity because of internal leakage.The balck box links in a 2.5k ohm resistor in place of the coolant temp sensor every time you switch on.This puts the glow plugs on and gives more pump advance - the combination should be enough to start the engine.When the coolant temp goes over 60c the engine ecu does not put the glows on and uses less advance.
So if your engine will start from cold there are 2 probabilities,first the hot start kit is not working properly,second the pump is so shot there still is not enough fuel to fire it up.Try squirting a cold hose pipe onto the injector pump for 5 mins when the engine is hot.If it fires up quickly you know the pump is worn.

Nice one thanks fot that.. I will give that a try.. Is the pump easy to replace?

nathan5346 · May 17, 2009

ive got the hot start box on mine, ive stalled it a couple of times when i restart i floor the accelerator when i turn the key and it starts fine dunno if that helps.

gavbriggs · May 17, 2009

mm, i have seen this issue on another diesel and the ecu had logged faults for something inside the fuel pump, dunno what as i lost interest when he said diesel pump!!! lol!!!

is the pump the same on the omega engines too?

i was told it wasnt an easy job and required locking tools???

Dr W · May 17, 2009

I've seen a few threads about it being quite pricey. I think I saw £1,200 for a new one and £700 for a s/h one.

SpudH · May 18, 2009

There is a different ECU fuel map for cold and hot.

Do a search on here under hot starting and you will find some very good info from around the time the hot start fix was developed.

There is a down side to having the hot start fix, I can't quite remember what it was. I think maybe the first fixes did not have a timer to switch the diode back out again after a few seconds and the cars ran on the cold fuel map and timing all the time doing damage to the engine. Just make sure your one has a timer in it.

It is generally accepted that the problem is caused as described above by a worn fuel pump and the only real cure is a replacement which requires special tools to get the pump timing right.

lanmjdun · May 20, 2009

Try www.dieselbob.com, that's where I'll go when my injection pump packs up...

I bought one of his bobbox devices and it does what it says on the tin, though that isn't relevant to this post.

chromiumuk · May 20, 2009

shaunm41 said:
Nice one thanks fot that.. I will give that a try.. Is the pump easy to replace?

It's a specialist job I believe, & if you are going for a secondhand pump, make sure it's the same part number.

zzr1200 · May 20, 2009

shaunm41 said:
ummm.. I think it might be a bit of trial and error then.. the hot start fix seemed ok till i jet washed the engine.. haha.. its a bit annoying if you stall at lights though as you have to wait till pre heat light goes off then give a further 3 seconds, otherwise you get endless cranking...

I'd be inclined to replace the hot start fix, its fairly cheap (25 quid-ish) as you have stated "the hot start fix seemed ok till i jet washed the engine..".

A little box with electronics inside probably not tested against a stream cleaner, theres a chance you've fecked it...

wantaquad · May 21, 2009

Hi Gents,
I have looked into the hot start problem at some length.
replacing the pump with anything other than a brand new item is unlikely to have much effect because..
BMW in there infinite wisdom programmed the ecu so that when the engine is warm it gets no preheat, no timing advance, and minimal throttle,
once you get a decent mileage and a little wear under the belt of your range rover, bmw 5 series or vauxhall omega Hot starting can become a bit of a problem.
Fit or make up the box - it works every time.
By the way - running cold water onto the pump only tricks the fuel temperature sensor (in the top of the pump) to believe the fuel temperature is very low and basically does the same as the hot start fix - if your pump is worn you will loose performance, and get lots of black smoke from unburned fuel because the injection timing will be late.

shaunm41 · May 22, 2009

zzr1200 said:
I'd be inclined to replace the hot start fix, its fairly cheap (25 quid-ish) as you have stated "the hot start fix seemed ok till i jet washed the engine..".

A little box with electronics inside probably not tested against a stream cleaner, theres a chance you've fecked it...

Yea i must admit, I didnt think the little box would be all too happy about having a bath, but i didnt think about it till after id done it lol..

shaunm41 · May 22, 2009

wantaquad said:
Hi Gents,
I have looked into the hot start problem at some length.
replacing the pump with anything other than a brand new item is unlikely to have much effect because..
BMW in there infinite wisdom programmed the ecu so that when the engine is warm it gets no preheat, no timing advance, and minimal throttle,
once you get a decent mileage and a little wear under the belt of your range rover, bmw 5 series or vauxhall omega Hot starting can become a bit of a problem.
Fit or make up the box - it works every time.
By the way - running cold water onto the pump only tricks the fuel temperature sensor (in the top of the pump) to believe the fuel temperature is very low and basically does the same as the hot start fix - if your pump is worn you will loose performance, and get lots of black smoke from unburned fuel because the injection timing will be late.

Ummmm well its either repair the black box, or buy a new pump.. I think it may have to be the box for now..

P36 BMW Diesel hot start..

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