Thanks guys, I appreciate your recommendations.

The scope test did not show any dead cylinders, all cylinders are firing. The spike on #8, at hot idle, is a little lower that the rest of the cylinders, but if you rev-up the engine, to 1500, everything looks perfectly normal. I am hoping the valves are not burned and that I have found this fuel starvation problem before the valves get burned.

No leak down test done.

The valve seals have been done at 207K KM. All plugs looked the same, slightly dark grey dusty. The plugs had been gapped to .032 inches but were re-gapped to 1MM, about .040 inches to get a bigger spark. I know the book says .032.

Unfortunately, I have been unable to find Chevron Techron up here in Canada. I added Canadian Tire (CT) Ultra fuel system treatment (C$14) just before filling the tank yesterday, and 200 km ago I added a bottle of Duralube advanced fuel system treatment (C$16). So now the full tank has about 1.5 bottles of the expensive cleaners. Both of these expensive cleaners say the bottle treats up to 70 litres of gas, the tank contains 90 litres. I bought 4 more bottles of CT brand normal injector cleaner (C$4) and I also have 2 bottles of STP injector cleaner(C$4). I wonder if the more expensive stuff works better than the lower price stuff?

I'll be taking her for a 500 KM run later this week. I didn't want to over do it with the cleaner. What is the maximum number of bottles recommended for a 1/2 tank fill-up? The cleaners never say what is the minimum amount of gas the bottle should be used in, they only say the maximum amount of gas it will treat.


I am now hunting for a used FD, estimated cost C$500. Estimated cost for a new one C$1,500, ouch!!

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1989 420 SEL