Did not ground Merc 200 xri plugs while checking compression

[bill200xri]

The Merc manual warns that I should ground the plug wires while cranking during a compression check. I did not notice this warning until I was done.

What components do I risk damaging?

I'm having high rpm issues, and wonder if I fried something.....

 

[Faztbullet]

Re: Did not ground Merc 200 xri plugs while checking compression

It is for safety so you dont get shocked and to keep any fuel exiting other cylinders when cranking from possibly igniting. You did not hurt anything . What type of issues you having?

 

[bill200xri]

Re: Did not ground Merc 200 xri plugs while checking compression

Thanks forthe response, Faztbullet

I have a top end problem...cannot accellerate over 3500 rpm. The motor starts to chug and the timing bounces around at that speed.

I plan to run test over the next day or so to complete DVA tests on coil input volts, switch box bias test, spark strength, etc.

I did stator and trigger resistance tests, and they are good. I did not warm them as part of my checks, however. I seem to be honing in on the switch boxes, but I was worried that I may have damaged the coils by not grounding the plugs.

Got any tips? I suppose I should monitor high pressure fuel pump pressure as I ramp up speed?

 

[sschefer]

Re: Did not ground Merc 200 xri plugs while checking compression

The Merc manual warns that I should ground the plug wires while cranking during a compression check. I did not notice this warning until I was done.

What components do I risk damaging?

I'm having high rpm issues, and wonder if I fried something.....

Technically the warning is about everything that's been said but it also helps eliminate noise with induction type timining lights.

 

[4JawChuck]

Re: Did not ground Merc 200 xri plugs while checking compression

If you do not ground the plugs while cranking you are essentially do a hi-pot test on the coil windings, the coils internal insulation can be damaged by not grounding the plug shell...its not wise to do on a regular basis.

It is extremely unlikely you destroyed/damaged the coils during a short cranking interval however if they were marginal before (from overheating or weak insulation) you can certainly do them in for good. Yes, I have done it accidently while testing. The good thing is if the coil(s) die while your cranking ungrounded they were probably bad to begin with...thats what I tell myself when it happens it makes me feel better.:redface:

It is very easy to test a coil and it can be done while installed with the factory specs in hand, if you are worried test them with an ohmeter to rule it out as a problem.