Compression Numbers?

[Tom L]

Hello All, I'm new to TDR but not to Dodge/Cummins! I have an 89 350 with 195m + miles. My question and I'll share some experiences; What is the normal compression in lbs for this motor with 150m plus miles? Mine has numbers from 340 to 380 dry and each cyl jumped 15-20 lbs oiled out. Now I have this to mention; around the 160-70m I changed inj nozzles, the motor was down in power is why, when I did that a serious miss type situation was obvious, but it ran like a new motor at road speed, just idled like a full race cam in a dragster. So next I was advised by Cummins I needed an inj pump rebuild, no change after that money went out of my possession, next a tech at a Cummins said I have air in the fuel system and he determined this by cracking the nozzle lines while motor idling, no change in motor on several. I've replaced lift pump several times and had some of the nozzles exchanged. Like I said, it runs like a champ going down the road with a full package but slobbers, overfuels, idles rough when cold, a little smoother when warm. My money is on compression is low when cold but would like to hear from others, especially like to know the compression poundage. Anyone looking for a clean 89 for a restoration? Tom

 

[nascar mark]

Tom,

Your compression isn't within spec for the difference between 340-380psi. The psi should be within 5% of each cylinder for a healthy engine. Your 380psi for your top cylinder is within spec for your high compression 89 motor and even the 340psi would be ok if all 6 cylinders were closer in psi.



My guess at your erratic idle would be that some or all of your injector lines ball heads don't point straight down into the bore of the injectors head. Loosen the nut of each injector line and move the nut up the line and see if the lines ball fitting is lined up parallels with the injector. (not cocked slightly) If the line isn't lined up and relaxing real close to the injectors head, bend gently until it does. Slide the nut back down the line and tighten back on injector while holding line down to line up. Repeat process for each line/inj.

 

[J DeMaio]

Tom:



I sent you a private message about the truck. Please send me a response back.



Thanks,



John

 

[dpuckett]

Tom L-

While I will not dare blaspheme Our Blessed Lady by questioning or trying to refute Mark's superior knowledge and experience, one thing that jumped into my mind was unbalanced injectors. Since you got them from Cummins, I assume they were recons, which dont have the best reputation on this board. Next question, was it idling rough BEFORE the new nozzles? If not, I'd say it is likely in your "new" injectors. I had this same problem in Mom's truck a while back when she got the injectors done- had to get one new tip, the rest just cleaned and recalibrated. Since that one new tip was possibly a HAIR smaller in hole diameter, it flows less fuel, thus upsetting the balance of fuel flow acorss the cylinders. Now, I DID do the injector line realignment this summer, and it helped, but didnt completely alleviate my problem. Timing advance helped a little, too. THere is still a slight lope at idle, but at least it doesnt vibrate you to death anymore. If you pinpoint the cause, let us know.



Daniel

PS- while you have the lines off the injectors, check the end of the lines for corrosion. Mine had quite a bit after only 10K miles form last summer. I sanded the corrosion off with some emery cloth, then rinsed them with liberal amounts of PB blaster and blue paper towels before even putting the injectors in the holes.