Low compression?? - Diesel Forum

ericjack · 07-04-2009, 03:33 PM

I did my head studs and a couple of "delete" things to my '05 back in March. I had the heads surfaced and several valve guides replaced. I've put approx 2,000 miles on it and now when I crank it, it sounds like it has low compression on one cylinder.

When it spins over, about every 2 seconds it sounds like the starter hits a "weak" spot....like one cylinder has low compression. It does'nt take long to crank so it's hard to catch it. Once it cranks it runs perfect....no miss or skip.

My local Ford Dealer says he can hear it, but has no clue what it is. One tech said a valve guide is wore, and once it starts the valve "centers up"...whatever that means, and closes up the compression leak.

It now has 45K miles on it. I did the stud job because of pushing coolant from the bottle. The heads were warped badly. Now I have NO coolant issues. All is good except for this sound when starting.

Should I ignore it or what??? Thanks for the info in advance.

nitrogen · 07-04-2009, 08:20 PM

doesn't make a lot of sense for a guide to be that bad if you just finished replacing the bad ones. unless whoever did them missed changing one he should have done or screwed up one he put in. is there any possibility what you are hearing is a slightly damaged tooth on the ring gear for the starter. if one tooth was cracked off you might hear a pause as it comes past the starter

ericjack · 07-04-2009, 09:43 PM

I took the heads to a Carquest Machine shop. He has a long history doing work for my local Ford dealer.

I don't think it is a ring gear problem. Have you ever heard a mechanical diesel trying to start after changing a fuel filter...and it's got air in the lines...and it's hitting on some and not the other? That's what it sounds like...like there's one hole with no compression, and when it comes to the top, there's no resistance and the starter changes tone.

My dealer says they can run a virtual compression test, whatever that means. Like I said it runs fine with no misses or skips

ericjack · 07-05-2009, 08:18 PM

Just an update...my truck had these three codes. P0231, P2614, and P2617. The 0231 is a fuel pump code. I think this popped up when I pulled the fuel pump fuse out to try spinning the engine over to hear the issue I'm having. The 2614 and 2617 are crank and cam sensor codes. Maybe this is the problem? Any help is needed.

Gofasterdammit · 07-05-2009, 09:14 PM

The P2614 and P2617 occurred because the PCM saw the engine cranking but did not start. You set those DTC's, I'd assume your CMP and CKP sensors are operating normally. Have the dealer do a relative compression test using the IDS. The test takes 10 seconds and will tell you if any cylinders are low. If the test indicates any cylinders have a concern, a manual compression test using a gauge will verify that. If there is a 0% leak down on all cylinders (according to relative compression test) then I wouldn't worry about it and keep driving it.