I have a 98 disco w/150k. The engine runs rough though no codes have been thrown. I had the mechanic do a compression test and #4 has 130lbs and #6 has 160lbs the rest are normal. Mechanic said it runs fine though he hears lifter nois and thinks a lifter is going out. My question is whether lifters would cause low comperssion or something else like the common issue of exhaust valves? Any expert advice would help before I pay for a top end rebuild($3500)
Thanks

 

I would first say that the one low cylinder is not real bad for a Rover, especially if it is carboning up. So that being said, It is time for a serious decarboning and a engine flush, pretty cheap to do and may correct your problem.
PM me with your tele.# and I'll call you and walk you thru it.
Mike

 

The compression values you gave lead me to think you may have a carbon and gummy deposit issue. When was the last time to added a good quality fuel injection cleaner product to the gas tank?. Like Chevron Techron or SeaFoam?

I run a bottle of Techron in the tank every four fill-ups. My Range Rover Classic is approaching 140K miles and is smooth and quiet.

I would change the oil and filter, add a quart of Rislone during that oil change (Of course that means using one less quart of oil than normal to allow for the Rislone), buy a couple of bottles of SeaFoam and follow the instructions to the letter. Then drive it for a week or so and do another compression test. I think you will be surprised at the result.

As far as the lifter noise, yes this happens with some frequency on the Disco at that mileage. The rocker arms themselves wear on the pivot bore that fits over the rocker shaft. And there was a situation with these engines of sticking valves. But do the engine clean and go from there.

Read my tech info sections at eurotekapg.com for more tips.

Regards,
Geoman

 

Thanks for the quick response. So far I have run 1 1/2 bottles of seafoam, engine cleaner and injector cleaner. Some difference but not much. If I have the mechanic do lifters & heads, do I need to do the cam as well? Will a bad lifter lower compression? If not my hope is I may need reman heads, rocker etc... and try to avoid paying the extra $1300 for cam and lifter. If I do need new lifters, do I need to do the cam as well? The mechanic says yes

Thanks
Davek

 

You can fit new lifters with the existing Cam, but never the other way around (new Cam with old lifters). Hydraulic lifters only really fail by "collapsing" which means they do not maintain pump up pressure. This results in an audible clicking -- and that valve does not achieve maximum opening. I've never heard of one lowering compression, which would mean that it would have to fail by locking up solid and not allowing the valve to settle on its seat at each cycle.

Geoman
www.eurotekapg.com

 

I would still do the engine flush as well as a good induction cleaning to help your engine out and possibly minimize unnecessary cash flow on your part.
Mike

 

What is the normal compression for a 4.0 L disco engine anyway?

 

9.35:1 = 170 to 180 lbf/in sq