Anomalous leakdown test result?

Jerome74911S · 09-23-2016, 11:57 AM

My 2.7 pulled a head stud. Before addressing that issue, a leakdown test was performed on the engine. All cylinders were from 2%, to 3+%, excellent - except one, that was 15% (and that one was not the one with the pulled stud). The curious part is that the leakage comes from the intake. At the same time, that intake track is clean as a whistle, with no oil or any other issue evident.

What could this be, and what should I look for?

strictly · 09-23-2016, 12:26 PM

If you havent pulled the heads off, you could do a leak down on the one with the pulled stud, and use some leak detector spray between the head and the cylinder. It seems odd that that one isn't leaking at that point - how did you know you had a pulled stud?

The one at 15%, are you sure it was only in the intake, and not also in the rings (crankcase breather). If its in the intake, try lapping the valve back into its seat, and reassemble and test.

My 2.7 had bad leak down on a few cylinders recently, the studs were fine, but it was blowing at one of the heads. I found the cylinder tops to 0.10" out of flat (flat bar accross, sag in middle one), im guess from mag case sag, anyway i managed to fix the head gasket leak, and then get the cam/cam tower torqued up without any binding of the cam. Its a temp fix till tear down time =)

My point, is while doing the leakdown, i decided to relap some of the valves (in my case an intake) to improve the leak down on some of cylinders that were otherwise good

yelcab1 · 09-23-2016, 12:28 PM

First of all, 15% is not a really bad number. Secondly, a tiny speck of debri can cause that.

Jerome74911S · 09-23-2016, 02:02 PM

Thanks for the responses.

First of all, contrary to certain wisdom, I re-torqued the cylinder head stud nut (exhaust) that fell off; twice it fell off. I did this to see if torquing could show me if there was any erosion damage anywhere there, but the leakdown showed 2% leakage on that cylinder. So, it seems to be holding pressure well. Unconventional, perhaps, but I did it.

I know that 15% isn't awful, but it is a bit odd when the other cylinders are so good. I do suspect that a speck of debris could have fallen into that intake, because someone had previously put some sealing glop on the somehow damaged intake gasket, which was sloppy to pull off. I want to peer down there carefully to see if I can pluck the debris out with some tweezers, if it exists.

It's a work in progress.