Diesel Engine Start-up, Revs High Briefly Then Ok

[BrianAll]

Hi, tonight after a 50 mile trip and a short break I started the engine of 90 BHP Diesel and the revs went up quite high when I started as if I'd put my foot hard on accelerator (say up to 3-4,000 revs) then ticked over fine i.e. just the one quick burst of high revs when turned over first time. Once started journey if felt very sluggish going up through the gears and was almost flooring it to get up to 70 mph. Feels as if the turbo is not helping out in the normal way. Haven't been driving it hard or heard any bangs/noises, etc. Have you got any ideas please ? Thanks, Brian p.s. just clocked over the 120,000 miles mark today during the trip. Coincidence ? Celestine Prophecy ? ;)

[Sher]

When I had problems with my Mass Air Flow meter (115bhp 1.9TDi) the engine would not rev over 3000rpm and it was way down on power. I was towing a caravan at the time.

 

I banged the MAF with the heal of my hand and immediately I drove away I knew the problem was solved.

 

I now carry a new MAF awaiting the time it goes faulty in a more permenant way

[Willie Krashitt]

Coolant temperature switch failed? Been covered a few times here. 3000rpm seems a bit high though - most reach around 2000. Does your temp gauge read normal? If it is the sensor (Vagcom or WDS will tell you) make sure you replace the sensor with one of the same colour, or it won't work properly. Been there, done that.

George.

[BrianAll]

Thanks Sher and Willie. I went to FAQ's after you suggested the MAF, then unplugged as suggested, and went for a spin. No change while driving, so sounds like MAF. The revving at start-up wasn't happening once MAF was disconnected, giving me more faith that it is the MAF. Now I will do the rounds with the local Ford and VW dealers and motor factors to see how cheap I can buy a new MAF for. Thanks for your help. Will post after I've replaced it to confirm outcome. I'm looking forward to my 90 BHP Diesel suddenly start to 'perform like a ferrari' when the MAF is changed, as suggested by another form poster elsewhere. I hope that doesn't mean 'spend loads of time in Ferrari garage being repaired'. Cheers, Brian

[mumof4]

Hold up........If you suspect the MAF, and you unplug it..if the car is worse then it isnt the MAF, if it performs marginally better then it is the MAF..but you say no change in the performance?..but it doesnt high rev when the MAF is disconnected?

 

 

Umm..i believe it twas me that made the ferrari comment....:lol:

[NikpV]

Hold up........If you suspect the MAF, and you unplug it..if the car is worse then it isnt the MAF,

 

 

not true - ours was worse when unplugged but sooooooooo much better with a new MAF

[mumof4]

Ahh..i stand corrected.

[gio]

Actually in the vast amount of typical MAF faults, mumof4 is indeed correct, but electronics being what they are,there will always be a few spanners in the works.Indeed you could add that many have changed their MAFs,believing that to be the problem and for a time it has indeed improved the running performance.Only for a loss of performance to return a few months latter and turn out to be another faulty sensor[not maf] bloody electronics.

[big_kev]

Agree with Gio on this, if you unplug the MAF and theres no difference ( or its better ) then your MAF has a problem.

 

If its worse then your MAF is probably ok but it might still have a problem....could be on the way out but not totally gone yet.

 

 

 

p.s. You been on holiday Gio....not heard from you for a couple of weeks....anywhere nice ?

[NikpV]

Actually in the vast amount of typical MAF faults, mumof4 is indeed correct, but electronics being what they are,there will always be a few spanners in the works.Indeed you could add that many have changed their MAFs,believing that to be the problem and for a time it has indeed improved the running performance.Only for a loss of performance to return a few months latter and turn out to be another faulty sensor[not maf] bloody electronics.

 

 

thick-film sensors sometimes degrade over time they don't always fail if you search here you will find a thread with acceleration and speed timings ...

 

oh btw it still has no performance problems 30k later be careful of making generalisations B)

[gio]

Agree with Gio on this, if you unplug the MAF and theres no difference ( or its better ) then your MAF has a problem.

 

If its worse then your MAF is probably ok but it might still have a problem....could be on the way out but not totally gone yet.

 

 

 

p.s. You been on holiday Gio....not heard from you for a couple of weeks....anywhere nice ?

 

 

 

Short break away in the caravan. but have been going through this sites threads A hell of a lot to read ! but a hell of a lot of good practical info too.

 

Right back to those threads,now where was i, yes bloody aircon problems! specifics, high pressure on low side, low pressure on high side!

[BrianAll]

Hello, thanks for replies. I purchased new Bosch MAF from local VW dealer for

[Sher]

Willie Krashitt Posted Oct 4 2007, 07:46:14

Coolant temperature switch failed? Been covered a few times here.

 

I've searched for "coolant temp switch" but cannot find another post.

 

Anyway to BrianAll use a multimeter to test the resistance when cold and hot, it should tell you it is a switch if the resistance goes between about zero and infinity.(open circuit).

 

I would NOT recommend shorting it unless you are sure it is a switch!

 

Perhaps just disconnecting it will help.

 

If it is not a switch but a thermistor, as I suspect, the resistance will change from a high to a low value when it is hot.

 

Values I do not know. Maybe someone else has the data?