Misfire on idle, goes away when throttle applied?

[NTHPL888]

Hi all,

I’m hoping for some help diagnosing a misfire on idle that goes away as soon as you apply the throttle.

Story goes - I recently put the car in the with the Indy for a service, MOT, check a possible fuel line leak and replace glow plugs. The car ran sweets as a nut beforehand although slightly down on power, perhaps due to minor fuel seepage.

Indy snapped a glow plug and couldn’t remove, called in a specialist to remove but that didn’t work and they had to remove the Head to remove the snapped glow plug.

Also had to replace the fuel pump, EGR valve and one fuel injector.

I got the car back and it’s got a misfire on idle, cars shakes all over the place but as soon as you apply the throttle it smooths out and drives fine, slow down and get near 1000rpm and it starts to shudder again.

Low compression has been identified, but all cylinders are fairly equal around 280psi.

Indy thinks it needs a full engine rebuild but as it was fine beforehand I’m unconvinced.

Any help or suggestions as to the cause of the misfire would be greatly appreciated - it’s taken a couple of months to get to this stage!

Thanks in advance.

 

[classiccarzone]

280 is not great compression but not fatal once all the cylinders are near to equal. It is amazing that a vehicle that was running perfectly, apart from being slightly underpowered, suddenly needed a fuel pump, an egr valve and an injector.

Assuming that the repair was carried out properly it would appear to be more like an engine mounting. A less pronounced fluctuation could be the fuel sensor at the rear of the fuel rail.

 

[DSM10000]

Your "Specialist" broke it, it is down to them to fix it. Was the injector the correct type? did it need calibrating?

Perhaps agree with the first one that another local MB mechanic could inspect it and give an impartial view?

 

[E55BOF]

The car was running well; the indie 'fixes' it; now it runs badly. In other words, there's a fault that wasn't there before it was 'fixed'. At very least, that casts some doubt on the competence of the repairer. Is he MB-registered, with a STAR, in which case the service he has just done will be recorded on the MB maintenance record for the car? If he isn't, I'd find another indie.

The slight loss of power could well be explained by the low compressions. I'm no expert on diesels, but if the compressions are all low, that suggests the engine is worn; how low they could drop on that engine, yet it would still run sweetly, would presumably give some indication of how worn it might be. It certainly didn't suddenly become worn to the point of not running properly while it was standing in the garage. Was the fuel pump changed because the delivery pressure was checked, and found to be too low, or just because "it's probably the fuel pump"? That's diagnosis by substitution, not by using the proper kit.

An engine rebuild would undoubtedly restore performance, and I suspect allow the indie to sort out whatever the current problem is, without the OP being any the wiser, but certainly a lot poorer. If it had spark plugs I'd look there, but since it hasn't, the 'new' injector would be my first port of call, followed by the 'new' EGR (or perhaps the other way around; as I said, I'm no diesel expert).

NTHPLL88, I'd go back to the repairer, politely tell him that you don't understand how the repair that he has done has led to a fault that was not there before, and ask him to explain to you how this could have occurred. If he's any good, he should be able to do so. If it's BS, there are experts on here that will spot it a mile off...

If he's a duffer, you may get nowhere, but it's worth a try. Let us know how you get on.