Todays big brain teaser!!!!!!

[turbopete]

As many of you are aware, i have a problem with air being sucked into the fuel when the engine is revved up ie when driving and often seems reluctant to start when facing downhill. this fact may or may not be relavant to this query.

on 3 occasions (so far) since ive had the car its failed to start, and been reluctant to the point of almost not starting on more occasions than i care to think about! this scenario of difficult/non start always occurs when the engine temp reads in the area of 80 or more on the guage. if i realise this fact before i flatten the battery too much, leave it to cool to 60 or 70 degrees it starts as normal (for my car that is, not normal for an e300td)

also over the last couple of days or so, it seems to have been running cooler than normal. this, again, may or may not be related. its always sat at around 80 on a run, slightly hotter with air con in use. lately ive used aircon every day and now its running at 70 degrees (on the guage) however the starting problem (my main concern) has been there since ive had the car!! can anyone shed any light on the problem? i cant afford to spend much as work is very limited, and what jobs i do get i need the car to be reliable to get me to them!

 

[Number_Cruncher]

Have you tested to make sure the cut off valve on the injecotr pump is being opened while you're cranking?

It would be short, simple, and cheap, work to rig up some speaker wire a resistor, and an LED which you could watch from insode the car to make sure that this valve is actually being commanded to open properly.

If you were to find the cut-off valve not being commanded to open, then, it would become a stronger possibility that the crank angle or TDC sensor is failing, which might also explain the temperature dependence.

 

[ALFIEBEARD]

Have you tested to make sure the cut off valve on the injecotr pump is being opened while you're cranking?

It would be short, simple, and cheap, work to rig up some speaker wire a resistor, and an LED which you could watch from insode the car to make sure that this valve is actually being commanded to open properly.

If you were to find the cut-off valve not being commanded to open, then, it would become a stronger possibility that the crank angle or TDC sensor is failing, which might also explain the temperature dependence.

That sounds feasible, I have known many electronic sensor
fail when hot, its usually caused by a tolerence change within the sensor itself, I work within the electronics trade and find that many components nowadays are very temperature sensitive, we use freezer spray and hair dryers in fault finding.
when it fails you could always try using freezer spray (available from CPC preston) or from me if you,re stuck peteand spray the sensors and see if they recover,
Regards
Alfie B

 

[jberks]

The incline issue - problem in the tank causing fuel starvation ?
Is the tank full?
As for temp - if air is getting in, it will expand at higher temps. bubbles that are close to causing an issue normally become large enough to make themselves known?

 

[turbopete]

the car does this whether the tank is full of otherwise. the cut off unit was replaced a few weeks ago when i changed the seal behind it as it started leaking after i discovered some bodging had been done and thought that this may have been the cause of my air ingress. i wondered about the air bubbles expanding. getting really annoyed with it now as ive changed everything in front of the fuel heater (clear pipes, seals etc) and air is visible running through all of them when the engine is running, changed the tank strainer and seal, so all thats original are the pipes/hoses from tank to fuel heater and the heater itself!!! as for the crank sensor, i wasnt aware these old generation diesels had them! would this possibly make it sluggish to start generally too? you may remember it misfires a little after standing a long time, eg overnight. not sure whats related and whats not!

 

[turbopete]

That sounds feasible, I have known many electronic sensor
fail when hot, its usually caused by a tolerence change within the sensor itself, I work within the electronics trade and find that many components nowadays are very temperature sensitive, we use freezer spray and hair dryers in fault finding.
when it fails you could always try using freezer spray (available from CPC preston) or from me if you,re stuck peteand spray the sensors and see if they recover,
Regards
Alfie B

i may have to take you up on that, especially if it gives up when im in your area!!!:lol::lol:

 

[wireman]

The crank sensor is I believe a hall effect device similar to the ones in early electronic distributor ignition systems (these were a known fail on hot device) several of which I have found to be at fault. On the one dodgy unit I managed to unpot I found that the wires from its internal circuit were badly attached and only held by the potting medium, so I suspect that (in this one case) this was the root of the temp dependent nature of the frequent fail to start when hot problem. If there is no electronic intervention on your fuel pump then this is I suspect a blind alley - dont go there unless your tacho is also playing up.

I agree with jberks about the vapour lock possibility with high under bonnet temperatures. Try opening the bonnet to see if it cools down any faster.

A partly crushed (or blocked) fuel pipe from the tank could be the culprit for your air in fuel problem, along with tired (hardened or splitting) flexi fuel hoses that the clips are not sufficiently sealing to their pipe ends. The increased vacuum from the fuel lift pump whilst reving the engine will try and draw air in through any hole it can.

If your temp gauge has started to read lower than it used to its either a temp gauge fault or (in my opinion most likely) a dying engine thermostat which should be changed.

 

[Number_Cruncher]

>>If there is no electronic intervention on your fuel pump then this is I suspect a blind alley - dont go there unless your tacho is also playing up.

The pump is under electronic control - there is an electrical shut off valve, and the rack position, hence fuelling amount, is controlled by a solenoid under ECU control.

I suggested this line of enquiry as Pete has been fiddling about with bubbles in the pipes for so long, (despite it being the work of moments to rig up a local supply from a tin) he might be becoming blinkered to other possibilities. It's also cheap, quick, and simple to test, and so can easily be tested and "eliminated from the enquiry".

I don't know if MB implemented this, but in the early to mid 90's when Euro II emissions came in, one way that truck manufacturers drastically reduced their enine's emissions was to prevent fuel being injected until the engine had done a certain number of turns under the starter motor, to get more heat from compression into the cylinders.

 

[turbopete]

the reason i wondered about whether or not there was a crank sensor was the fact that this is never a problem when its running, only on a hot start. the reason i never tried running the car on a seperate fuel supply is plainly because due to lack of income, i dont want to have to cut any newly replaced pipes if at all avoidable and as far as i can tell, theres no other way to attach a new feed to the fuel system except for at the tank side of the fuel heater which on first appearances seems to need the manifold off to access it, however i may be forced to do this if time allows this weekend. the car is used most days a number of times a day etc. as regards the tacho, its always worked fine, but then again, so does the engine as long as i dont try to start it above 80degrees. its really messing with my head now!

 

[ALFIEBEARD]

i may have to take you up on that, especially if it gives up when im in your area!!!:lol::lol:

Hey Pete,
You are more than welcome mate, we use the stuff all the time so will always have some in and you could give it a quick squirt and see if it helps, we are in Lowry Hill its RETEL ELECTRONIC SERVICING, pop in anytime.

Alfie B

 

[Number_Cruncher]

>>i dont want to have to cut any newly replaced pipes

You wouldn't necessarily need to.

 

[turbopete]

anyone know if the wiring is easily accessible to the crank sensor so i can test its resistance if it fails on a hot start? or if its difficult to start when hot?

 

[turbopete]

any takers?

 

[turbopete]

also, which wires on the 4 pin plug on the fuel cut off switch are for the shut off valve and which are for the fuel temp sensor im told that is part of it?

 

[turbopete]

anyone advise on the best place to start with this? ive got prices for fuel heater and crank sensor. £40-odd each. should i replace 1 or both? if just 1, which should i try 1st?

 

[ALFIEBEARD]

COME ON LADS REPLY TO THE BLOKE!!!.
WHERE,S TELEVISION WHEN YOU NEED HIM PETE

WISH I KNEW PETE BUT I DONT.
Alfie B

 

[turbopete]

no worries Alfie, i may end up just replacing everything i can buy at this rate!!!! besides im getting used to no response with this one now! i need the car too often to mess about. i dont do huge mileages as a rule but i do use the car a lot and due to family illness i need it to be 100% reliable, or as near as possible!

 

[boschbrakes]

I have a 99 ML430 that wont start hot. I found the ECU blower inop. It was very random but ultimately realized it was the heat. My truck runs the ECU fan as soon as the key is turned on and then for several minutes after the key is turned off. The ECU and Cruise computers sure do get hot. I am thinking of adding another blower to the box to give it extra cooling. I live in a hot environment. It took a while to come to this conclusion as it was so random. Hope this helps. Good luck.

 

[turbopete]

I have a 99 ML430 that wont start hot. I found the ECU blower inop. It was very random but ultimately realized it was the heat. My truck runs the ECU fan as soon as the key is turned on and then for several minutes after the key is turned off. The ECU and Cruise computers sure do get hot. I am thinking of adding another blower to the box to give it extra cooling. I live in a hot environment. It took a while to come to this conclusion as it was so random. Hope this helps. Good luck.

thanks for the pointer. living in the uk, the temp never gets too hot really! however, in this instance it seems to be engine temp related as opposed to ambient air temp related. once temp guage reads above 80c it gets harder to start. the higher it goes, the worse the problem is. its failed to start 3 times now, and in each case the temp has been reading approx 90c. summer, winter, makes no difference. if the engine temp is up, it wont start. leave it an hour or so and it starts ok. not as it should, perhaps but it will at least start! i must have a friday afternoon car! or a hungover on a monday morning car! cant decide which!