P38 '95 4.6 misfire

Checked leads / plugs, misfire on No. 2 cyl. RH side looking from rad. Tested another coil pack but same problem, no spark. Multimeter on coil pack showed all OK apart from that connecting to No.2 lead which was dead. Understand that if it starts OK (which it does) then the ECU is OK.

Any ideas please?

Sorry, think its a Gems coil ~ the straight one. Just wondered what course of action to take having studied other posts / threads. Should I go for a compression test or get a very expensive auto electrician involved? Is it likely to be the lead from the ECU to the coil?
(I have had a lot of water leaks into the footwell ~ a new windscreen sorted that).
I think the auto electrician might be better as he will come to me and I don't want to burn-out the cats going anywhere else.

Any response will be gratefully received 'cause I'm scratching my head, not knowing what to do.

maelstrompat said:

Checked leads / plugs, misfire on No. 2 cyl. RH side looking from rad. Tested another coil pack but same problem, no spark. Multimeter on coil pack showed all OK apart from that connecting to No.2 lead which was dead. Understand that if it starts OK (which it does) then the ECU is OK.

Any ideas please?

Click to expand...

No response.....have I posted this in the wrong section?

83 views and no replies............nobody likes me?!

Perhaps I need a lesson on 'How To Win Friends And Influence People'

Tried to keep things to the point but perhaps that was wrong.......maybe I should gone into great detail about the idiots who have 'worked' on my Rangie to date and what it has cost but I thought that may be wrong as you've heard it all before!

Oh Well........no help here.......I'll keep scratching my head.

There dozens of possibles, too many for posting.

Have you tried a substitute lead set? Does it have a distributor or is it 'lost spark' ignition?

If it has lost spark ignition as per the Thor 4.0, there is no distributor and each coil has a plug at each end and is not grounded, the pair of plugs fire at the same time, but only one is on a firing stroke. Causes occasional burping on the overrun if you have a leaky LPG valve that lets gas in when it shouldn't!

So, you need to check the lead for the bad cylinder AND the lead for the opposing opposing plug. The pairs are: 1+4, 7+6, 5+2, 3+8.

If you have a distributor, ignore that.

Peter

So the spark plug is not sparking? or is it sparking, if so the cylinder has no compression? try sticking a spark plug into the lead and earth it out on the exhaust manifold, and see if you get a spark. No spark=electrical fault. Good spark=compression fault. easy.

listerdiesel said:

There dozens of possibles, too many for posting.

Have you tried a substitute lead set? Does it have a distributor or is it 'lost spark' ignition?

If it has lost spark ignition as per the Thor 4.0, there is no distributor and each coil has a plug at each end and is not grounded, the pair of plugs fire at the same time, but only one is on a firing stroke. Causes occasional burping on the overrun if you have a leaky LPG valve that lets gas in when it shouldn't!

So, you need to check the lead for the bad cylinder AND the lead for the opposing opposing plug. The pairs are: 1+4, 7+6, 5+2, 3+8.

If you have a distributor, ignore that.

Peter

Click to expand...

Many thanks for your reply.
No LPG.
Wasted Spark technique. Direct Ignition System.
No distributor.
Eliminated the lead as a problem by removing existing and trying a new lead, same result ~ no arc to the plug. This, having rigged up another coil pack and plugging in with the existing pack in place, as removing the existing pack (close to the bulkhead) is not straightforward. Then scoped the coil socket and found no voltage, so the problem seems to be either in the ECM (?) or in the wiring to the coil pack. I have had problems with relays and I wondered if the ignition relay would affect the coil pack. As I say, my knowledge is limited.
Cheers
Pat

v8hotrodboy said:

So the spark plug is not sparking? or is it sparking, if so the cylinder has no compression? try sticking a spark plug into the lead and earth it out on the exhaust manifold, and see if you get a spark. No spark=electrical fault. Good spark=compression fault. easy.

Click to expand...

Thanks for your response. has to be an electrical fault ~ no power to the one of the coils (rest OK)
Cheers,
Pat

maelstrompat said:

Many thanks for your reply.
No LPG.
Wasted Spark technique. Direct Ignition System.
No distributor.
Eliminated the lead as a problem by removing existing and trying a new lead, same result ~ no arc to the plug. This, having rigged up another coil pack and plugging in with the existing pack in place, as removing the existing pack (close to the bulkhead) is not straightforward. Then scoped the coil socket and found no voltage, so the problem seems to be either in the ECM (?) or in the wiring to the coil pack. I have had problems with relays and I wondered if the ignition relay would affect the coil pack. As I say, my knowledge is limited.
Cheers
Pat

Click to expand...

Did you check the opposing plug and lead?

You can check the coils easily enough by flashing them with 12V across the centre and one outside pin of the 3-pin connector.

There are/were two big suppression capacitors in the loom, if one of those has gone faulty that would affect things. They are taped into the loom round the back of the heads.

Peter

Short answer is no. As mentioned earlier, work to date was done by a local garage who did not have a clue, paid them, tried to drive out and things were a damn sight worse, drove back in and told them to sort the leads which they had mis-connected, they had to download a diagram as they had got totally confused. They gave me a phone number of a mobile auto-electrician (who did not want to know, saying he did not have the dianostic equipment), he then gave me another contact a few miles away, spoke to him and he's looking at it next Tuesday. Told him I was concerned over driving it to him due to the cats and he advised dis-connecting the injector on number 2 cyl as it wasn't firing anyway.

Any advice you can give will be printed out and I'll take it next Tuesday.

My thoughts on the relay ~ is that a possible cause?

Complete bloody mess at the moment..........

Where are you based?

The cats are possibly cooked now anyway, you've been playing around for a while now.

Peter

If No 2 has a misfire then am I right in thinking that no 3 (corresponding cylinder) should also have a problem and those two receive the same spark (wasted spark system).

listerdiesel said:

Where are you based?

The cats are possibly cooked now anyway, you've been playing around for a while now.

Peter

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Exeter, Devon

Quite agree re cats and can't work out how to unclip the injector leads anyway!

MattMatt said:

If No 2 has a misfire then am I right in thinking that no 3 (corresponding cylinder) should also have a problem and those two receive the same spark (wasted spark system).

Click to expand...

This what listerdiesel said earlier:
"So, you need to check the lead for the bad cylinder AND the lead for the opposing plug. The pairs are: 1+4, 7+6, 5+2, 3+8. "

So, is it not 5 & not 3? Or am I confusing matters (again!)
Thanks fpr responding Matt

Pat

From RAVE: (up to 99my)
QUOTE:
The electronic ignition system uses four double ended coils. The ignition coils are mounted on a bracket fitted to the rear of the engine. The circuit to each coil is completed by switching within the ECM, allowing each coil to charge. When the ECM determines the correct ignition point, it switches off current supply to the coil which in turn causes the magnetic field around the coil's primary winding to collapse, inducing HT voltage in the secondary winding and in the iron core of the coil. High tension voltage, of different polarities, is produced at either end of the coil's core and is transmitted to two cylinders similtaneously, one on compression stroke, the other on exhaust stroke. This is called the wasted spark principle.
Note that coil 1 feeds cylinders 1 & 6, coil 2 feeds cylinders 5 & 8, coil 3 feeds cylinders 4 & 7 and coil 4 feeds cylinders 2 & 3. The resistance of the spark plug in the compression cylinder is higher than that in the exhaust cylinder and hence more spark energy is dissipated in the compression cylinder. Coil failure will result in a lack of ignition, resulting in a misfire in the related cylinders.

unquote.

Therefore I assume that Matt Matt is correct in saying that:

Quote:
"If No 2 has a misfire then am I right in thinking that no 3 (corresponding cylinder) should also have a problem and those two receive the same spark (wasted spark system)."
unquote.

Pat

I was looking at the Thor engine coil connections, sounds like the early P38's are different in how they arrange the coils, apologies.

Peter

Peter

No problem, I am very grateful for your input.

Pat

So if no3 is ok could I suggest the injector. I have a light tester that plugs into the injector wiring to make sure it working - not the injector itself but the wiring. It showed up an intermittent problem on mine that turned out to be a connector. I can't remember what it was called but dead cheap. Been in my tool box ever since.

Oh and the other thing. I had a misfire on no2 but ( the shame) I had a spark leads mixed up

MattMatt said:

So if no3 is ok could I suggest the injector. I have a light tester that plugs into the injector wiring to make sure it working - not the injector itself but the wiring. It showed up an intermittent problem on mine that turned out to be a connector. I can't remember what it was called but dead cheap. Been in my tool box ever since.

Oh and the other thing. I had a misfire on no2 but ( the shame) I had a spark leads mixed up

Click to expand...

Mat

Now that's a thought ~ will check the injector lead on Tuesday (Before if I can get the light tester) . Know the feeling re leads mixed up !

Could you tell me how to unclip the injector leads, I know its basic stuff but I can see there's a metal clip involved but not sure if you squeeze it of have to use pliers or if you just pull it ~ forgive my lack of skill please!

Pat

You are best carefully removing the retaining clip first, as the plug won't normally pull straight off the injector.

The clips are 'aerobatic', they will spring away and get lost very easily, so be careful, and also remember which way they go on and replace as soon as the plug is off the injector.

The injector wiring on the D2 is not easy to get wrong as the leads are not long enough to get out of sequence, don't know about the earlier GEMS engine.

Peter