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[demonicwillow]

Jheeps been running high exhaust temps since it catastophically broke down a few years ago its also down on pulling power, on its own its not so bad but pulling the caravan or trailer it really struggles on the hills, my mondeo pulls the van like a train with no issues so its not the van.

Ignition and fuelling appear to be fine so im left with burnt exhaust valves, a timing chain thas jumped a tooth or the chain has stretched or both causing the fuel to ignite in the pipes or a dodgy CPS but I think thas ok.

Any idea what the ecu controls the basic igniton timing at ?? maybe able to check it with me strobe.

And if the chain had jumped a tooth how bad would the engine run, im wondering if the ecu is correcting the timing enough for it to run sort of ok.

[Mike Pavelin]

Partially blocked exhaust?

[demonicwillow]

Exhaust is completely clear, had it all off today to gut the Cat, the silencer is the straight thru type so no baffles inside to get bunged up, took it round the block, seems a bit better but not brilliant, my guess is some sort of valve issue, another leak down test tomorrow maybe I think.

[eastryjeep]

First principles would say to do a nice cheap compression test and see if anything obvious shows itself.

[demonicwillow]

Compression test shows about 110 to 120 across all 6 but I did do it cold  Ill have another go tomorrow with a warm engine, must admit I took it out just now and its going better with the cat gutted out, I could see daylight right thru all the honeycomb crap but its possible it was blocking up when extremely ridiculously hot.

[eastryjeep]

Ok, compression test will only show peak values achieved, but wont show if valve overlap has been compromised somehow. Now that it seems to have cooled down it might be a good idea to get the emissions tested for unburnt hydrocarbons, the cat might have been getting clogged by unburnt fuel and now youve gutted it the engine will still be carrying the same problem, it's just that youve temporarily removed the symptom.

[demonicwillow]

It passed its mot friday and flew through the emissions test as clean as clean can be, im still putting my money on the valve timing, either jumped a tooth or stretched chain, and the fuel is firing off down the tubes, as I need the truck for some towing jobs over the next couple weeks im loathed to pull the rocker cover off yet to check when the valves are on the rock, will do it soon tho as its bugging me now.

[Delk]

The 4.0 has steel gears and unless it was put together wrong the cam will be close. Everyone worries about it skipping a tooth but this does not happen. They either work or break. They can get a bit slack from streaching or some makers usea plastic covered gear that can break away.

What was the failure?

[Bubba]

had a 360 v8 skip but never an in line six

[Delk]

Out of all the engines I have never seen it and still don't believe it. The chain would have to skip on the smaller gear. That would still leave about a dozen teeth to jump at one time. That's an extremely loose chain since it would have to be stretched alot.

I have had several really high mile engines break chains. But these all made so much noise there was no suprise when it happened.

[Bubba]

i remember it well so does my wife ...........we were on honeymoon in our 79 fsj

[demonicwillow]

The 4.0 has steel gears and unless it was put together wrong the cam will be close. Everyone worries about it skipping a tooth but this does not happen. They either work or break. They can get a bit slack from streaching or some makers usea plastic covered gear that can break away.

What was the failure?

Whilst negotiating telegraph hill in devon one very snowy wintery day whilst on cruise control a few yers back and me not thinking proper, as it began to slow down from 80 it changed down as one would expect but went straight to first gear  engine over revved itself into submission for a split second or so until I hit the brake pedal to cancel the cruise but too late, a loud pop and it died, got it to the side of the road and had a look under the bonnet, there was bits of airbox everywhere, shrapnel, to cut a long story short the over revs caused the distributor to seize, the shaft was forced upwards into its own body the dizzy shaft helical gears were stripped nicely, no damage to the cams helical gears, the repair was straight forward enough, popped another distributor in and started first time, then found the top of the oil pressure sender had burst open due to the over revs ...

help 



being recovered, and I was absolutely frozen by then



dizzy



Due to the distributor seizing but the engine still turning it fired off a spark to an open cylinder igniting the lpg vapour within the manifold, blowing the airbox to bits, all in all it was a shite just before Christmas day, went back down to Mum n dads after xmas and fixed it but its never been the same since, this is the reason why Im thinking some sort of valve timing issue, wont know till I open it up tho I guess.

[Delk]

At high revs the 4.0 cam flexes because it does not have enough support. That's why you ate the dizzy drive and also the reason the engine has a low rpm limiter. I am not sure if cam flex is permanent or not or what issues it causes.

I know of some swamp racing guys that add extra bearings and support to the cam. They raise the rev limit to around 7 or 8 grand. But this is huge money and the engine starts to look really messy with small external oil lines feeding the extra bearings and special cam.

Timing is set by the flywheel and ecu. You can move the distributor a good amount and it will not change the timing. Inside you only have the sensor to show the cam position so the correct cylinder fires.

The cam gears also fail if you are running high volume oil pumps. It puts more stress on the gear then its designed for. Lucky enough it happened less then 100 yards from my house.

[demonicwillow]

Since I gutted out the cat it seems to pull much better on its own, may do a dummy caravan run n see if there is any improvement when under load, the pipes are still running very hot tho, compression and leakdown checks arent showing anything drastic, dont have anything to check the fuel trims as its obd1, is it possible to do this if I obtain the correct diagnostic connector and summat that will read the info ??