Thoughts on a recent compression test

[srgtlord]

So my 1.6 started running rough recently and I thought the old injectors or low compression may be the culprit. So I pulled the injectors and did a compression check to verify the health of the engine. The results were cyl #1 350psi cyl#2 475psi  cyl#3 475psi cyl#4 375psi. Should I be worried about the lower compression in cylinders 1 and 4 ?

[Dakotakid]

This was running-warm or very near operating temp?
Or cold?
I ask as I check both.
Added: I believe the accepted variance is 75 lbs.
How new or fresh or intact is the tester you are using? Is it having any problem with the quick connect joint or anything like that?

Is it safe to assume you worked across the block.....like 1 through #4 sequentially? And not like #2 and #3 and then the other two...as batteries often weaken and cylinders lose their lubricity with rotations.

[srgtlord]

The engine was stone cold when I did the test. I did not check the cylinders sequentially. I checked 1 4 2 3. The compression tester was purchased from napa a year ago.

[Dakotakid]

Does this head have solid lifters?
What are your valve clearances?

It will be useful to see how much the end-cylinders will come up with running heat.

[srgtlord]

It is a hydraulic head

[burn_your_money]

You had all the injectors removed for all the tests? Can you retest with it warm?

What were the numbers like last time you tested?

[ORCoaster]

According to the Bentley the wear spec is 398 psi.  Anything lower is a problem needing to be addressed. 

It might be a pain to do but go back and see if doing cylinders 2 and 3 first change your numbers.  Do #s 1 and 4 last. 

But from all looks of it you have worn rings that need attention.  Or maybe rings that are not free to expand to the outside cylinder walls.  That black coke stuff is nasty business on rings. 

[srgtlord]

Ill retest the engine in a week once I get new heat shields. This engine has well over 250,000 miles on it by now so it would not surprise me if the rings were worn.  On a positive note I believe I did solve the rough running issue.  I put brand new bosch injectors in the car and it seemed to run much better but 3 out of the 4 new heat shields leaked combustion gasses terribly and bubbled diesel right where the injector meets the head. Gotta love brand new defective parts...

[ORCoaster]

I always reuse my heat shields.  I make sure that the center is touching and I can see just a sliver of daylight on the edges.  When using a steel ball, a socket and vise grips there is no need to by new ones.  I wouldn't trust new anyway.  Would still check for fitment upon installing. 

[libbydiesel]

I put brand new bosch injectors in the car and it seemed to run much better but 3 out of the 4 new heat shields leaked combustion gasses terribly and bubbled diesel right where the injector meets the head.

It's funny how many times I've heard people say that.  Bubbling diesel where the injector meets the head is NEVER from a compression leak.  A compression leak will not bubble it will blow puffs of air too strong to form bubbles.  When diesel bubbles from where the injector meets the head it is because you spilled diesel around the injector threads and it sat there in the threads until you started the engine.  Then with the engine running, the injector tips got hot enough to start the diesel at the bottom of the threads to boil.  The boiling diesel formed bubbles you could see. 

As for your compression check, if you tested it cold, then probably a few of the lifters were bled down from cam lobes pushing on them.  Those cylinders will show low compression until the engine is run, the oil pressure comes up, and they pump back up.  The spec is for a hot compression check because a cold compression check doesn't give accurate or useful information. 

[srgtlord]

According to google diesel boils between 360–680 °F. I was seeing these air bubbles immediately after I started the vehicle after I installed the new injectors. Should I just ignore these diesel bubbles?

[libbydiesel]

Yes, you should ignore those bubbles. 

[burn_your_money]

No, fix the fuel leak.

[libbydiesel]

No, fix the fuel leak.

Indeed, if there is a fuel leak, fix it first and then ignore the bubbles around the injector threads.

[srgtlord]

I will definitely fix any leaks and will replace the heat shields on cylinders 2 3 and 4 for peace of mind. At this point Im just happy the car still runs at all. Ill report back with my results. FYI new bosch injectors use a 28mm socket instead of the 27mm. I did'nt have a 28 so I had to use the closest standard socket I had.