I'm trying to help a buddy diagnose his '90 non-intercooled. He has a miss-vibraion through the entire rpm range. He bought the engine used (he converted a Suburban) and doesn't entirely know the history. So, since he thought it would be fun, and since he thought the old injectors might be a bit lazy, he installed a new set of Bosch 190s. That didn't help his missing problem. So my thoughts are: bad valve(s), bad piston ring, bad head gasket, or something in the injection pump. My understanding is that the only way to get a miss on one cylinder from the injection pump is if the "delivery valve" spring (is that the same as the "starting spring"?) is bad or broken or if the delivery valve is stuck. Correct me, please, if I'm wrong.

He's very good about engine maintenance and checking things out...to a fault even. But I told him to check (again) for any leaks on the high pressure side, do a compression test, look for coolant leaks, coolant contamination, oil contimation (head gasket). If the delivery valve is to blame, that can be replaced without pulling the pump, correct?

Thanks much.

 

I may have missed it but did he check for fuel , equal at all lines ? to confrim fuel problum , then compression , the delivery valves are just under the lines coming out of the pump , I try to give you a site to check out ,its about timing , but it give details about r&r.
http://www.dodgedieseldatabase.com/
Dodge Diesel Database

 

You are right that the only way you can have a miss on one cylinder with good injectors is if the delivery valve is bad for that cylinder (because the VE pump only has one piston & cylinder that is used for all the engine's cylinders).

Assuming it misses on the same cylinder all the time:

I would start by letting the engine idle, and cracking each injector line at the injector in turn. If you are lucky, all but one will make the engine run worse.

BE CAREFUL OF HIGH PRESSURE FUEL -- it can cut, maime, kill, etc.

If this turns up nothing, check the compression. Cheap ways to do this are: barring the engine over 2 full revolutions by hand (or if you have a manual transmission, put it in third, and coast down a hill with the engine turned off and the clutch engaged).

If it is missing randomly, then you might have a bad injection pump, fuel leak, clogged filter, etc.

 

He already did the routine with cracking the lines before he replaced the injectors. He determined then that it was, in fact, just one cylinder. I don't remember which one. That's why I'm hoping, for his sake, that it's a delivery valve. Seems like that would be the cheap and easy solution. At least the cheapEST and easiEST. I'll talk with him tonight and see if he's learned anything.

 

Could be something as simple as a bent push rod or a broken valve spring. Possibly if the engine sat for a long period of time a valve may be stuck, found that a lot of times on gassers. Like was said a compression check is in order to eliminate a lot of these things. A delivery valve on a 90 engine is not a cheap easy fix, a pump rebuild would be in order.

 

I am going by memory, but is seems to me that I read somewhere, that if the fuel line is not aligned properly with the injector it will mimick a miss. It may be worth a try - could be a cheap fix.

 

If u are getting fuel to that cylinder thats missing at the right pressure. Take off the vale cover and have a look at the intake vale I've had trucks come in with lot's of miles and have woren out rocker arms check the ex side to. Wish u the best of luck.

 

the delivery valve is outside the pump housing.
unscrew the injector line at the pump, then unscrew the small tube coming out of the pump on that injector line.
be carefull not to lose any parts there is a small spring, a valve and a brass compresion washer. if you take it apart, get a new compression washer to insure a nice tight seal.
all this can be done without removing the pump.
good luck
jeff

 

check all the push rods