Air trapped in H.P. Lines?

[lberch]

Is it possible for air to get trapped between the injection pump and the injectors for a long time???



I have been working a miss at idle for five months. It only misses at idle and has never missed loaded or unloaded at a higher rpm.



I just fitted two mechanical 0 - 15 psi guages through A/C hoses and fittings to both Schrader valves.



At idle (warm) I get 11 Psi (pre) and 10. 5 Psi (post) filter. The readings are never more than 1. 5 Psi different, so a restricted filter is not an issue.



Both guages read very steady until the engine misses and I get a . 75 Psi spike INCREASE (post) and a . 5 Psi INCREASE (pre) filter. And it doesn't miss consistently, it can go for several minutes between misses.



Reving to 2500 rpm (static) netted 9 Psi (pre) and 8 Psi (post) filter. Not bad I thought... . Until I drove off... .



On a short trip (below) 50 mph I did a couple of WOT and the pressures went as low as 4 Psi (pre) and 3 Psi post filter. I know, I know, everybody is going to say those pressures are too low and that my lift pump is in the way out @ 27,000 miles, but it never missed above idle and it pulls hard!



So I removed and tested the overflow (return) valve on the side of the pump and it seems to hold until about 15 Psi which is in spec.



I am thinking that my next step is to start cracking injector lines to see if I have any entrapped air between the pump and the injectors. How big of a long shot is it to have air trapped between the pump and the injectors for an extended period of time?



LB

 

[Whitmore]

Iburch, I would think it would work its way out but I aint no pro so lets take it back to the top and get more help... ... ... ..... Kevin

 

[lberch]

Back to the top!



If its not entrapped air, would cracking the injector lines help isolate if I have a bad injector?



LB

 

[LSMITH]

LB, if you have a bad injector cracking the lines will help identify it, basically listen to it and if one line does not change the sound of the engine you know what cylinder it is.

I think I would adjust the valves first though, if you have a tight valve (no lash) it will act the much the same. The cylinder will be low on power at all RPM but is nearly impossible to tell as speed increases.

If it is not solved by a valve adjustment and the sound does not change on one cylinder swap that injector with another using new washers. If the problem moves you are in good shape, a $50-60 injector is all you need.

If the problem stays get a compression test on that cylinder or pressurize it. A dead hole is usually an injector but could be a burnt or bent valve, possibly a ring or cylinder problem too. An air pressurized cylinder will tell you if it is a valve and which one, or if it is a more serious issue. Make sure all 4 valves are fully closed and put a rubber tipped air nozzle in the injector hole, if it starts to turn the engine over reduce the air pressure. You should hear no air leaking in the intake or exhuast systems.

There will be some air leaking into the crankcase. Aside from a compression test or using a manometer to measure the air blowby I don't know how to tell how much is too much. Hope this helps.



Be very careful cracking the lines, there is enough pressure there to get hurt bad, even die if you get shot up with diesel.



EDIT: spelling error

 

[lberch]

Thanks LS, I will go the route of cracking the lines and if no joy, will check where my valves are at and adjust accordingly.



LB