V8i 4.0 Auto "Misfire"

The saga of getting my V8i Auto 4.0 (D2/2000) running properly continues. Over last 2 months have replaced front exhaust section (aftermarket cat section, but refitted old llambdas), identified failed cylinder head bolt and consequent failed gasket (repair involved helicoil / new gasket etc), replaced both coils and all HT leads to cure subsequent misfire on all cylinders, all spark plugs also new.

Before work on block/head, but also with new front exhaust section, engine ran rough (unsurprisingly given failed gasket - cylinder 5 issue) but certainly was able to rev all the way. After work done, however, new problem is whilst engine runs V8 smooth at idle and on revving in N, when in D will only run smoothly up to about 2000 revs / 50 mph. Then simply "misfires / stalls" and refuses to go any higher / faster. Kickdown will not work at this point.

Dealer workshop staff seem stumped: they did a fuel pressure test and swapped in/out new fule pump but no joy on that angle. I've read all the posts I can find on this site on the subject but have seen nothing that is quite like this. Have played around myself with running in all gears (1 / 2 / 3): first gear seems to allow revving all the way up to 4000 plus, but under load even that fails (kickdown on steep hill); 2nd / 3rd bring back the problem even more readily. Also tried switching in the cruise control and then using that to increase speed - while it sat happily at 50mph/2000rpm, all hell broke loose when tried to increase, and it took a few minutes after turning it off to return to earlier conditions. Have also looked at air filter - not an issue.

Ideas welcomed. I've spent a fortune on the engine etc over past 2 years and this is getting to be nearly the last straw! In particular, not sure why it will apparently allow full revs in N but not when moving. All comments welcomed!

How much you wanting for it?

Not so fast, my friend!

Since its Sunday, I've invested a few more hours reading: have disconnected MAF sensor - and low and behold an immediate improvement. Not perfect (still hunting up and down), but can now get full revs in D and kick-down operates.

Any further thoughts, anyone - other than taking advantage of this poor reader?

Duff spark plug? Might be new, but you can get duff ones out the box!

Also something I just though of, get the dealer to do an adaptive reset on it and get a new MAF meter, I'm not sure if there is a way to do the adaptive reset without going to a dealer (maybe take battery off?), someone will know mind you!

This is Def a MAF related issue. Replace would be the easiest option. Not sure if the V8 maf is a "hot wire"?

Encouraging to have someone who knows what he's doing give a clear prognosis!

Will try cleaning first, plus try my best to check the harness.

Not many Discos locally, to try and blag a quick cross-test using a good MAF sensor, but will do my best. Are these sensors ubiquitous - or unique to each model? Presumably if Bosch also make them then they fit may makes / models.

Success! At least holding up well initially. Thanks for the tip about MAF - plenty of advice and comment on this site on symptoms, cleaning, etc.

Gave it a good blast of Carb Cleaner; disconnected nattery for a couple of hours to see if would help adaptive reset; and now drives like new.

Will be having a word with the LR Wkshop that it has sat in for last 4 weeks .........

Thanks GFD and Briggsy.

Redman said:

Success! At least holding up well initially. Thanks for the tip about MAF - plenty of advice and comment on this site on symptoms, cleaning, etc.

Gave it a good blast of Carb Cleaner; disconnected nattery for a couple of hours to see if would help adaptive reset; and now drives like new.

Will be having a word with the LR Wkshop that it has sat in for last 4 weeks .........

Thanks GFD and Briggsy.

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where are you based , if someone has a hawkeye with the V5 software then they can clear your fault codes and reset your adaptions

Andy