4.7 V8 running rough

[Anjam]

Guys,

I have a year 2000 4.7 Petrol/LPG Amazon which was serviced/MOT'ed a few weeks ago. On the way back from the service/MOT the car started running very rough right through the RPM range including idle. I took it back to the service garage and asked them to have a look and they say they can see nothing wrong other than a leaking exhaust manifold and this will be causing the engine to run rough. The manifold has been leaking for nearly two years and other then a ticking sound when cold I have not noticed any other issue with the car running. I don't want to spend the £500 or so in changing the manifold if the cause is something else.

The car runs rough on petrol and lpg so it is not the lpg system. Could the crack suddenly have caused the engine to run rough? Is changing the manifold my only option? The garage seem to think so. It is taking a couple of extra cranks to fire up so I am thinking it maybe fuel related.

Any ideas?

 

[BRE Fabrications LTD]

Does it run rough right through the rev range?

If so could it be a misfire? Check all the plugs to the spark plugs and coil packs.

Also would be worth checking all your vacuum lines, if a hose has accidentally been pulled off it could cause rough running. Seen it on a carb motor before...

If the "roughness" clears at higher revs you could be experiencing a flooding condition in one of your cylinders. Possibly damage or a short to the injector cable. With your lpg conversion your injector wires would have been tapped into for a signal to control the lpg injectors. If these were not well insulated and possibly disturbed at all during the service that could cause a petrol injector to open even when running on lpg. If you check your spark plugs and find one thats all sooted up that would be an indication of too much fuel...

Just a few guesses based on my experiences with my petrol/LPG 80 series so far.

 

[Anjam]

Thanks for your input, it does run rough though the rev range. I will get the mechanic to check the vacuum lines before investing in the Manifold. Can the coil packs be visually inspected or only through diagnostics? The mechanic did say that that he hooked it up and could find no fault codes, there are no dashboard indicators either that highlight a fault that the ECU can detect.

Any Landcruiser experts in the Berkshire area?

 

[Gav Peter]

Check out ZuesV8's thread on this problem for some potential hints & tips AJ...

 

[Anjam]

Thanks, I also changed my battery. How does leaving the ignition on for six minutes help?

 

[Gav Peter]

Fraid I have no practical experiences to offer man... Yet...

 

[karl webster]

Maybe something to do with the ecu`s keeping contact with each other?????

 

[Zeusv8]

I had a similar problem too, must be v8 versus LPG thing. I had to have the base idle reset and the lpg recalibrated which seemed to work but I still have an intermittent problem in traffic where the revs drop slightly then jump a bit so that the needle is almost bouncing but no roughness. Might be worth having a diagnostic done on LPG system to rule it out. I had a dodgy live wire which was causing four cylinders to fire irregular. The 6 mins thing is for the Ecu/ immobiliser and other wizardry to wake up and talk to each other!
Oh and I never had a fault code or check light!

 

[Gav Peter]

Thanks for chiming in Jim...

Update that sig line whenever you see fit ;-)

 

[Zeusv8]

Still hate the bastard and love it and hate it

 

[Anjam]

Thanks for the help.

I will try the 6 minute re-sync. Mine is rough all through the rev range, like it is running on half the cylinders. Does the same when LPG is switched off, could it still be the base idle and LPG calibration? Can we rule the Manifold out? The manifold has been ticking for over a year, I would have expected a gradual increase of noise and deterioration of performance, this was just sudden after the MOT/Service.

Can anyone recommend a decent LPG diagnostic shop in Berkshire?

 

[Dark Dude]

BTW: What make and type of LPG system are you running on your truck? The best recommendation I can give you is Neil at Medway DualFuel but maybe it's best you take it back to where the conversion was originally done.

John

 

[chugga90]

Morning,

Several answers from my experience.
The battery disconnect matter, when reconnected both of my cars I have had needed the ignition left on after conection to recognise the chip in the key I am lead to believe.
The rough running, does it feel like a vibration when going along and need a lot of pressure on the loud pedal to get it to shift along? If it is this my first car had this and it was the coil packs. These did not show up on diagnostic tests on the 98 R plate and were found by swapping out a good one for each one until found. Do buy good quality replacements as the cheap ones do not last long at all.
I think one of the members Warrenpro has a diagnostic machine and he is berkshire?
If it is running the same on both fuels then would think it is not the LPG that is the issue, have used Oxford Autogas, based near Thame oxfordshire, they are good at problem solving but are usually busy.
Just had both manifolds off of mine and new gaskets done, this has solved the cold start up ticking which was the gasket material rattling, but the amount of work to get at them was more than the cost you indicate!
Hope this helps?

 

[Anjam]

It feels exactly how you describe, car vibrates and takes a lot of effort to get along.

Many thanks for the feedback, I will pass on to my mechanic and get him to check the coil packs too.

 

[chugga90]

Not sure what mileage your car has done, but the ones I had trouble with had done 115 to 120k miles and I think were originals.
When it did it the first time I thought I had a flat tyre because it vibrated so much!

Good luck

 

[Anjam]

The fault was down to failed coil pack, I hadn't changed and the car was perfect for a few weeks and then another failed which I changed. Another one went today. What could be causing them to go suddenly? None of the replaced ones have failed yet.

 

[Jon Wildsmith]

They do tend to go in batches, all the old ones being the same age, so that's probably all it is.

 

[chugga90]

I agree with Jon, its age that has caused them to expire. When mine started I changed all the ones in one bank of cylinders, working out which were good and saving for a spare in case of later issues.
I was told that if you are running with failed coil packs it put extra load on the others and caused them to fail, but not sure if this is true of Toyota parts department trying to sell more of them!!!!!!!!!!!!!!!

 

[prav]

I had mine 4.7V8 converted in 2011 at AUTO GAS 2000 at Carlton Miniott Thirsk North Yorkshire tel 01845 523213 speak to John real honest yorkshireman will tell you what he can do and won't rip you off. So far my brother and I have had conversions done and he drives a Lexus LX300 and runs really well like mine. Its a long way up north but could be well worth it..