Stuttering and backfiring

OK so after I bought a new set of leads to help with the erratic idle and was waiting for them to come, it's developed another problem. Anything more than very gentle application of the throttle and it stutters then starts to backfire if you push down any harder. Fitted the new Magnecor leads, no difference. It's drivable in 1st to 3rd gear but chronic when it drops into 4th.

My immediate thoughts are crank or cam sensor or MAF. Hoping it's not cam sensor having just seen the price.

1996 4.0 so chassis code TA.

It's nigh on undriveable, does it on petrol and gas and I have to switch it over to petrol to just about limp it up hills on the motorway.

Don't think me completely mad but would a head gasket blown to atmosphere cause it?. Last week I discovered it had lost 4 1/2 litres of coolant without a visible leak. All blown back as far as I could see through the header tank overflow. Discovered a dead thermostat so changed that. No blow back of air into the tank whilst running, no water on the dipstick, some mayonnaise inside the filler cap and left bank breather but the weather's been a bit chilly so not necessarily a surprise. Have cleaned it out and am monitoring.

Getting a bit desperate as the other car's also off the road.

Anthony

Do a compression test, you may have a cross blow between two cylinders that has compromised the water jacket.

Thanks.

Would that cause the stuttering too?

ajsphead said:

Thanks.

Would that cause the stuttering too?

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Oh Yes....

ajsphead said:

Thanks.

Would that cause the stuttering too?

Click to expand...

It certainly would.

Oh bollocks. Looks like it's time for an uprated cam and lifters then. Will do the test tomorrow when (if) I get home from work and then we'll see.

ajsphead said:

Oh bollocks. Looks like it's time for an uprated cam and lifters then. Will do the test tomorrow when (if) I get home from work and then we'll see.

Click to expand...

It may not be that, but compression test is a place to start if you have a misfire and back fire. If the compressions are ok look for something else.

Try cleaning your maf sensor.mine done this ,it was like loading up and the more you pressed the accelerator the worse it got and would then backfire,I cleaned mine by spraying brake cleaner in and blowing out with an airline,don't know if this is best way to do it .but worked on mine and still ok.

Did a compression test. 7 cyls showing a lovely 180psi,1 showing 145psi. A bit of scratching around has also foubnd the cause I think. 7 spark plugs showing a nice brown deposit, 1 looks almost new. First thing I did when i bought it last year was to change the plugs. 7 came out normally, 1 did not. Took it to my local specialist who shifted it after 1 1/2 hrs with a breaker bar. Popped new plug in and things improved. The old one was completely burnt out and had been there for goodness knows how long. Didn't worry too much as it was running better. But when I took a look yesterday, the new plug was not seated all the way into the cylinder head and judging by the lack of deposits, had not been firing properly into the mixture or sealing properly. The thread in the head is f****d.

So we have a reason and an explanation. Thanks for your help. As luck would have it, a mate has just picked up a breaker with a good working engine, not sure if 4 or 4.6 so there's a replacement head ready to go and maybe some other bits too.

Next, time to find a good uprated road cam to help overcome the GEMS flat spot.

ajsphead said:

Did a compression test. 7 cyls showing a lovely 180psi,1 showing 145psi. A bit of scratching around has also foubnd the cause I think. 7 spark plugs showing a nice brown deposit, 1 looks almost new. First thing I did when i bought it last year was to change the plugs. 7 came out normally, 1 did not. Took it to my local specialist who shifted it after 1 1/2 hrs with a breaker bar. Popped new plug in and things improved. The old one was completely burnt out and had been there for goodness knows how long. Didn't worry too much as it was running better. But when I took a look yesterday, the new plug was not seated all the way into the cylinder head and judging by the lack of deposits, had not been firing properly into the mixture or sealing properly. The thread in the head is f****d.

So we have a reason and an explanation. Thanks for your help. As luck would have it, a mate has just picked up a breaker with a good working engine, not sure if 4 or 4.6 so there's a replacement head ready to go and maybe some other bits too.

Next, time to find a good uprated road cam to help overcome the GEMS flat spot.

Click to expand...

There you go. Bit of good old mechanicing and you found the cause.

Am a bit nervous about the complexity of P38s compared to the other stuff I have (SD1 & Classic Saab 900), so prefer to ask before assuming I know then creating an expensive cock up.

ajsphead said:

Am a bit nervous about the complexity of P38s compared to the other stuff I have (SD1 & Classic Saab 900), so prefer to ask before assuming I know then creating an expensive cock up.

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The engines mechanics arn't complex at all, pretty standard stuff. It's all the electricary that's a pain in the arse.

The thread in the head may be able to repaired with a Helicoil and depending how easy the access is maybe done in situ
[ame="http://www.youtube.com/watch?v=RFYa6sjhh_E"]How to Repair Threads With A Heli-Coil Insert - YouTube[/ame]

ajsphead said:

Did a compression test. 7 cyls showing a lovely 180psi,1 showing 145psi. A bit of scratching around has also foubnd the cause I think. 7 spark plugs showing a nice brown deposit, 1 looks almost new. First thing I did when i bought it last year was to change the plugs. 7 came out normally, 1 did not. Took it to my local specialist who shifted it after 1 1/2 hrs with a breaker bar. Popped new plug in and things improved. The old one was completely burnt out and had been there for goodness knows how long. Didn't worry too much as it was running better. But when I took a look yesterday, the new plug was not seated all the way into the cylinder head and judging by the lack of deposits, had not been firing properly into the mixture or sealing properly. The thread in the head is f****d.

So we have a reason and an explanation. Thanks for your help. As luck would have it, a mate has just picked up a breaker with a good working engine, not sure if 4 or 4.6 so there's a replacement head ready to go and maybe some other bits too.

Next, time to find a good uprated road cam to help overcome the GEMS flat spot.

Click to expand...

I had similar with my disco, i retapped the thread

It's been a while, but I finally got the old engine out ready to put the rebuilt one in. I knew it wasn't going to be good and I'm glad the old engine is going for scrap. Exhaust valves not seated properly, lots a resin deposits and nasty orange stuff in the combustion chamber which I think is caused by an additive in cheap petrol (which I don't use). Everything looked and smelt cooked under the valley gasket, 3 slipped liners and the oil on the end of the head studs smelt more like paraffin.

RIP