Forum:
Hi folks, I've got a persistant misfire on my 2.8 non turbo.
Having checked valve clearance and replaced the injectors I've done a compression test before I go and start investigating a possible new Injector pump.
The tech spec on this website says that the compression should be 32 bar.
I've got 30, 30, 32, 34.
Are these figures ok or should they be closer to tech spec.
Your help would be grealy appreciated.
Many Thanks,
Chris.
Plus or minus 10%
These figures seem OK.
Normally for measurements such as this, an accuracy of +/- 10% is pretty good, and you're well within that.
Is the misfire evident at tickover? If so, try to locate the offending cylinder by undoing each injector feed in turn. Yes, the injection pressure is something like 2500 psi, but the quantity is small, so if you undo the injector feed nut smartly, all that will happen is that diesel will dribble out of the joint.
If you stop the injection on a good cylinder, the engine will tickover noticeably more unevenly, but if you stop the injection on a duff cylinder, there won't be much difference.
The next thing to check is to swap the injectors between the duff cylinder and a good cylinder to see if the fault moves with the injector (which it shouldn't because your injectors are new, or are they the same ones merely re-conditioned ???).
One silly thing springs to mind ... the glow plugs run red hot with the heat of combustion and provide a convenient ignition site to ignite the charge reliably. If the plugs haven't been touched for years, one might have eroded away to nothing and be failing to do it's secondary job. OK, the beast will tend to start on 3 cylinders, but you might just associate this with an old diesel banging and clanging on normal startup.
I have no experience of injector pumps dying, so I can't help any further on this. I'd be interested to find out what the problem is in the end.
I've tried swapping the injec
I've tried swapping the injectors about just in case one of them is a dud but it's made no difference. The misfire is'nt prominent enough to notice on idle, It's more noticable between 1200 - 2000rpm (where you drive most of the time) I'm certainly going to examine the glow plugs to see what they are like, If one of them is eroded that might explain a little drop in compression too. However there are 2 cylinders which are both down 2bar (30) and they are next to each other. I'm considering the possibility that maybe the head gasket could be slightly leaking between these two cylinders.
I'll check the glow plugs, See what happens ..........
Thanks for the reply.
Glow plug test
Hi, I've checked all the glow plugs (and swapped them around) and they are all fine. It's made no difference. I guess it's time for a headgasket check unless anyone else has any other ideas?
Thanks for reading. Chris .
Hmmm bit of a head-scratcher.
Yes, I thought I would suggest something easy to do before the heavy-duty stuff like whipping off cylinder heads.
It's no joke when you find that you have taken off the head (and paid £40 for a gasket from Milners) for something that was fixable without.
Working on the idea of minimum cost, I guess the head gasket check is the better thing to do, because an injection pump (the other thing you were thinking about) is certainly going to cost more than a head gasket. The other thing is that I've rarely heard of injection pumps going wrong .... can't say the same for head gaskets though.
The other thing I thought about was the possibility of burnt exhaust valves, but you will have to take the head off to check these too.
Sorry I haven't been too much help so far.