Classic Misfiring at 2-3000rpm

ukadamwest said:

not solved..

misfiring again.

and the P38 is misfiring too.
can someone tell me why we like these cars ?

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The challenge and satisfaction when they're running correctly!

now strangely, when I took for a run down the road yesterday after doing the fuel pressure regulator it was running fine, this morning it was back to misfiring.

to replace the regulator I pulled the MAF, the plenum chamber, plenum trumpets and fuel rail with the injectors on after which it ran fine down the road and back, after sittting overnight its back with the misfire.

What are the wires to the injectors like? Brittle?

Grrrrrr said:

What are the wires to the injectors like? Brittle?

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No not at all.

I'm wondering if the removal of the fuel rail emptied out the residual fuel hence it ran ok immediately after but in the morning back to a misfire once the pressure had built up again.. with a blocked fuel return causing the overfuel.

ukadamwest said:

No not at all.

I'm wondering if the removal of the fuel rail emptied out the residual fuel hence it ran ok immediately after but in the morning back to a misfire once the pressure had built up again.. with a blocked fuel return causing the overfuel.

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Good thought!

See told you it was the ecu...
Bet it just kicked in to life triggerd by the MAF change obviously

Is there any way of measuring the fuel pressure while it's running? A gauge in the cabin, check the pressure on a run, allow to settle overnight and see what changes, if anything? Don't these have a fuel temperature sensor? What is it's purpose? It senses the change in fuel temp and adjusts the injector pulsing according to temp. It's likely it's causing it to over fuel, but at the wrong temperature....

Update...

Having had a discussion with Saint.V8 the only thing we could work out was the change in RPM having been through everything else was the distributor.

Pulled the distributor a few weeks back as there was a lot of slack in it.

So brand new distributor put it in static timed it. Then dynamic timed it taxed it took it for a run...

Big difference. However it does misfire still at 2000rpm but back off and re accelerate and it gets past the misfire.

And to add insult to injury... the water pump has just started leaking.

Edit to add: just running it in the garage.. tweaking the throttle it's quick and responsive with no misfire. Yay !

I still have a curious misfire with George (2000 V8 THOR) starts & idles perfect hot or cold. But between say 900rpm and 1500rpm there is a hesitation that's getting worse. BUT... It doesn't happen all the time. Perfect when cold and warming up. Pull away from stop and she almost stalls, popping from the exhaust, then 1500rpm and she's off like a scalded whale!

I was waiting for a mate the other evening, revved the tits off her next to a Mustang (well, be rude not to...after all, George sounded MUCH better ). So mate arrived and we set off, I said watch this.... NOTHING! No hesitation, no miss, no pop just perfect behaviour The fuq??

Doo said:

I still have a curious misfire with George (2000 V8 THOR) starts & idles perfect hot or cold. But between say 900rpm and 1500rpm there is a hesitation that's getting worse. BUT... It doesn't happen all the time. Perfect when cold and warming up. Pull away from stop and she almost stalls, popping from the exhaust, then 1500rpm and she's off like a scalded whale!

I was waiting for a mate the other evening, revved the tits off her next to a Mustang (well, be rude not to...after all, George sounded MUCH better ). So mate arrived and we set off, I said watch this.... NOTHING! No hesitation, no miss, no pop just perfect behaviour The fuq??

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When did you last change your spark plugs? And if you open the bonnet in the dark on a damp night, can you see little blue sparks anywhere?

Brand new plugs & leads 8k miles ago. At 1st, I thought it was due to the hose blowing coolant all over the place. But it was dried by the time I replaced the hose. Then I blamed the throttle body dripping onto three leads on the left bank, but again all fixed, no more leak, but misfire slightly worse. There are no discernible sparks... However, the leads do seem a little bit tight for my liking, but they are grey and allegedly for this engine. I wonder if they need replaced with original parts?? I'll visit Hamish Monday because it's driving me nuts. Funny how it sometimes doesn't do it at all though!!

Doo said:

Brand new plugs & leads 8k miles ago. At 1st, I thought it was due to the hose blowing coolant all over the place. But it was dried by the time I replaced the hose. Then I blamed the throttle body dripping onto three leads on the left bank, but again all fixed, no more leak, but misfire slightly worse. There are no discernible sparks... However, the leads do seem a little bit tight for my liking, but they are grey and allegedly for this engine. I wonder if they need replaced with original parts?? I'll visit Hamish Monday because it's driving me nuts. Funny how it sometimes doesn't do it at all though!!

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I would try new plugs and leads as a first port of call.

With all the technical experience behind the advice on here my own contribution will be insignificant, but when you use the term 'miss-fire' do you mean a regular miss (like one or more cylinders not firing) or more of a 'splutter/back-fire' scenario ? As for the 'nearly new coil' I'd still try a known good one for elimination, the same applies to the AFM & ECU if you have access to them. I'm know I'm asking for flack here (head protection WILL be worn) but I've never used anything other than Champion plugs on a standard engine.

Could be your MAF starting to fail doo if you have a laptop and an odbII cable I can give you a link to my Dropbox with a good generic software that allows you to see run data like MAF readings and O2 sensors and resetting basic codes.

No OBD cable, but Hamish is a decent bloke so I could ask him to do a quick check. I'll try unplugging the MAF and see if it makes any difference.

It definitely feels like sparks, but she runs so sweet otherwise

Doo said:

I still have a curious misfire with George (2000 V8 THOR) starts & idles perfect hot or cold. But between say 900rpm and 1500rpm there is a hesitation that's getting worse. BUT... It doesn't happen all the time. Perfect when cold and warming up. Pull away from stop and she almost stalls, popping from the exhaust, then 1500rpm and she's off like a scalded whale!

I was waiting for a mate the other evening, revved the tits off her next to a Mustang (well, be rude not to...after all, George sounded MUCH better ). So mate arrived and we set off, I said watch this.... NOTHING! No hesitation, no miss, no pop just perfect behaviour The fuq??

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If it's automatic, don't rev it too much out of gear, kills the box apparently.

Wazzajnr said:

If it's automatic, don't rev it too much out of gear, kills the box apparently.

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True, I've seen this advice from ZF in the distant past.

Wazzajnr said:

If it's automatic, don't rev it too much out of gear, kills the box apparently.

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Can see it causing damage in Park but even in neutral?

Grrrrrr said:

Can see it causing damage in Park but even in neutral?

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Park and neutral are the same condition, only the park pin is engaged in park on the output shaft.
I seem to remember that it's something to do with lack of clearance to the brake bands when they're not controlled and they can grab and strip the lining, I may be totally wrong on that though.
I do know that they aren't supposed to be reved much in park or neutral though.

I wasn't quite right, it's a problem with the pressure not being bled off from the first clutch pack after a gear has been selected. So, if you do want to rev it, the recommendation is to switch off the engine for 60 seconds then it's safe to rev to 2000rpm for up to 90 seconds providing no gear has been selected.
Applies to park and neutral.