Hey guys,

There was an inital miss in the A-bank.

I just went through the old girl and replaced the injectors, new distributor cap and rotor, new leads.

Thinking that 'd fix it!! Well it seems to have worsened. (I think it may just be more noticable because its all running better now).

I'm hoping its not that she's dropped a valve. Maybe timing?

Any ideas of where to look next?

Cheers

 

Steve,

PreHE are not known for seat dropping.

With it running, lift the injector plug clear of the injector, one at a time, and when you find the one that makes NO difference to the oddity of the engine, you have found one. Now work out, is it spark, spark plug, lead, injector, injector voltage issues.

My PreHE's ALL fouled spark plugs with the greatest of ease. Sooooo, when you find one, remove the spark plug, bet its sooty, clean it, replace it, start the engine again, and continue with the diagnosis. I know they are new, but that negates nothing, they foul plugs, especially if started and shut down prior to reaching operating temp, which is normal when first bringing one back to life.

Check the firing order, and that the leads are in the correct hole, it is easy to get it wrong.

Timing generally does not cause a drop of cylinders.

 

Cheers.

But mine is an '88' so is HE.

And I tried pretty much what you suggested but disconnected the leads one at a time and found no change. Which struck me as very odd.

I'm pretty confused right now. I may just sit down and go through it all again. Plugs out and cleaned. Leads checked. (Got to admit I hated doing the plugs!! Lol)

 

Bugga,

Yep I forgot AGAIN.

HE, still foul plugs, and make sure you are gapped at 0.025", or they run crappy, especially at idle.

The HE also is soooooo easy to crack a plug when installing them. I remove more than most when changing plugs, just to be sure.

Misfiring has to be either plugs or injectors. OK, some other stuff comes into play, but basically those 2 items are the prime cause.

General rough running is many, many items.

ECU fuel pot adjustment
TPS split voltage out of idle range.
Throttle plates incorrectly set.
Timing to a certain point.
Vac leaks, of which there may be many
The module inside the ignition amp may be getting hissy.
Engine earth straps, not completing the earth path.
Coil, or coils playing up.
Over run valves in the front of each inlet manifold are leaking, if you still got them.
PCV system gone AWOL. The valve sometimes get replaced with Holden, or Ford valves, they will not do the job.

 

Mmmmm, reading some more about that oddity when disconnecting the leads, that is odd, you should feel a distinct engine change.

Maybe the injection loom in the bottom of the V is shorting. This is soooo common. Old age, oil cooking the loom, and the rest is history.

 

I would be very suspicious of the injector harness, yes. If it was the root cause of the initial misfire (which is certainly plausible) then changing the plugs, wires, and injectors may have put it over-the-edge (just from jiggling the crispy wires around a bit) and thus the problem is now worse.

Cheers
DD

 

So how would I test this? Where can I get a new loom from? And how pricey are they?

 

A rudimentary test would be to jiggle the injector wiring a bit with the engine running. If the engine reacts to the jiggle test, you've hit paydirt. However, lack of engine reaction doesn't prove the harness is good.

The other choice is to remove the harness and for inspection. I can all but promise that you'll find many areas where the insulation is cracked open, exposing bare wire which can ground out against the engine.

New harnesses are available...about $600 I think. Most everyone makes their won for a fraction of that amount. Not hard to do, really.

Cheers
DD

 

Testing, no idea. I have heard of a "noid light" that mimics an injector pulse,a nd I suggest one, or more, that is not doing the right thing would be clearly visible.

Basically if I suspect an EFI loom issue, and that is most, I undo it from the bottom of the "V", and carefully lift it out, and carefully strip back the layers of insulation, and molten stuff. This generally exposes bare wires and even broken wires.

I located (long time ago) some injector plugs/terminal in kit form that fit our VL Commodore (Nissan EB30 engine), and they fit the HE injector clamp oddity perfectly. Bosch make EFI plug/terminal/boot as a kit, and that would be the way these days I reckon. Some "modification" of the plug may be required for our injector clamp, basically cutting a small section off to clear that plate, not rocket science.

I then purchased some decent 3mm wire (Narva brand), and sat down one wire at a time and made my own. I made it so as to have the loom up under the inlet manifolds, basically on top of the camcovers, and wrapped the finished product in "header wrap tape". The first was not to my liking, so a second followed the next day, and that is on the car still.

That was 14 years ago.

I did heaps of loom/wiring alterations at the same time, but that may confuse too many people, so I will not elaborate.

I have seen looms on "&bay" at times, but no idea of quality or anything else. Maybe Jagdaim, or H&H spares have looms, never asked.

They are NOT hard to make, time consuming, YES. Understanding of soldering iron proper use is a must.

 

So I fiddled around with the loom front to back and started to get a miss in the b bank not nearly as bad but I think I may have to look at that now...maybe make a replacement over xmas

 

If it were me I would be more inclined to first find out which of the injectors is misfiring.

A while back I had a V-12 that had this mysterious miss fire and I went the whole route of removing all the wires and inspecting them. A lot of work to find nothing.

So I started all over again but this time starting at the other end, with the injectors themselves. Using a mechanics stethoscope fitted with a probe (a long screwdriver will also work) I listened to each injector to make sure they were all clicking. Found the one that was misfiring and on removal simply found it to be plugged.

While pulling everything it to replace it, I grabbed the opportunity to install all new soft pliable fuel injector hoses between the fuel rail and all the injectors. The old brittle ones are a definite fire hazard on the V-12 which makes them way too dangerous to ignore.

 

My previous post most probably would have made more sense had I added that I had allready changed all the injectors on my car to find that it had only made the misfire worse. So I started hunting.

 

I have already changed them...but hey anything's worth a shot.

Something else for everyone:

I let the old girl sit for a full day without tinkering started her up. And there was no miss..the second the engine got a bit of heat in it (ie the exhaust gasses started to blow hot) the miss came back!!

Any further thoughts?

 

OK, I am reading that a few times, and I know yours is a HE, but here goes.

One of our PreHE's did very similar, and I thought I had done all possible and would have to live with a 11.5cyl V12.

For some reason I put my timing light on each spark plug lead, and observed the "flash", and noticed 5A was erratic as the engine got hotter. This stuff was all new, as with yours. I thought in the direction of a sooted spark plug would also give that status, coz a "non-firing" plug will do that. Pulled the plug, good as, so found a grubby old lead, fitted that, all good.

The HE did give some grief once, and I listened to the injectors "click" and 6B was not as "clicky" as the rest. Took a small tack hammer (it was handy), and "smacked" the injector, it came good, miss gone, and still untouched today.

Another thought is the ECU idle fuel pot adjustment, just wondering if it needs "tweaking" a tad to alter the mixture to eliminate the "miss".

i will keep thinking as a sample a new Canadian Club, mmmmm.

 

Only problem with running a V-12 with a miss is that you will eventually kill the catalytic convertor. That of course only applies if you have them fitted the cars down

 

Hey guys,

Its been a while I know, just never seem to have the time I think I will. But such is life.

So I have Figured out it is cylinder 6A that is the culprit.

Checked the lead it works.
Checked the plug. (besides being slightly fuel fouled had a fairly strong spark)
Did the screw driver on the injector trick. (prior to removing the plug)

So where to next?
Compression test I guess?

Any ideas?

Once again guys I really appreciate the help

 

BUGGA.

Compression test is now a #1.

Screw in tester only, just in case, as 200+ is normal on a HE.

The fact it got air/fuel/spark, but no "fire" really only leaves compression, or lack of, big time.

I will keep thinking as I sort a MB Diesel that has a wicked vibration, box of matches me thinks, cheaper all round haha.