Compression test with weak starter

[The Warden]

Hello!

Due to concerns over water injestion, I'm preparing to run a compression check on my truck. Only problem is, I found out today that my starter's on its way out. It's spinning the engine fast enough to light off, but the starter's definitely revving slower than before. I think this was me trying to start it without any glow plugs or ether last week and not letting it cool off between cranking as much as I thought I had.

The good news is, it looks like my starter's on a lifetime warranty, so it won't cost me any $$ to replace it. Given the abuse it's seen, I'm surprised it did as well as it did.

So, my real question here is, will the slower-spinning starter throw compression numbers off? I want to make sure I've got the numbers right, but it'd be nice to not overwork the new starter too much...so, unless the numbers will be off, I'd like to run the check with the old starter.

Thanks!

 

[F350camper]

I'm without a doubt not an expert in this area, but it would seem to me that if you had all the GPs out, and the compression tester hooked up to one gp hole, the lack of compression on the other cyls would allow the starter to spin fast enough to get a good reading.

Just my free advice, but you get what you pay for.

 

[argve]

Me as well not expert but isn't it still pulling in the same amount of air and trying to shove it into the same small space just slower so wouldn't the end pressure still be the same? Just gets there slower... Don't know but to me it seems you would/should get the same numbers.

 

[The Warden]

I'm thinking the same thing myself...

I'll just run the test as-is, and if the numbers come out low, I'll put the new starter in and see if that makes a difference. I've got compression numbers from before last summer, so I have somewhat of a basis of comparison...

Thanks again

 

[WPineF]

with a slower starter the numbers might be lower but you should still be able to pick out a low cylinder as being different from or lower than the others.
just my 2 cents

Dave