Engine/Transmission (1994 - 1998) Low compression when cold

[McLaughlin]

I have a buddy of mine that took his 2nd gen CTD to a shop because he had low power when the truck was cold but it was fine after it warmed up. The shop told him he had low compression when cold due to "blow by" which self corrected as the engine got warm. The shop installed new/high performance injectors which they said was a "low cost" fix because of better atomization of the fuel.



Is it a common thing for CTDs to develop compression problems when cold that go away when the engine warms up?



Also, I'd be interested in the forum's thoughts regarding installing new injectors as a inexpensive fix.

 

[Johnstra]

This is actually the first instance of excessive blowby/low compression I've heard about on a cummins. I guess if the engine was dusted, it could have low compression on one or more cylinders. New injectors seems like a bad fix though. Even with big sticks and more fuel the compression problem would still be there and would probably still be just as noticeable.



How did the shop diagnose low compression? Did they actually do a compression check? Have they done a crankcase pressure test? That's usually a better test for excessive blowby on a diesel.



What shop was it, btw?



-john

 

[McLaughlin]

This is actually the first instance of excessive blowby/low compression I've heard about on a cummins. I guess if the engine was dusted, it could have low compression on one or more cylinders. New injectors seems like a bad fix though. Even with big sticks and more fuel the compression problem would still be there and would probably still be just as noticeable.



How did the shop diagnose low compression? Did they actually do a compression check? Have they done a crankcase pressure test? That's usually a better test for excessive blowby on a diesel.



What shop was it, btw?



-john

That was my impression also. Shop apparently tested for low compression but I'm not sure if there was a crankcase pressure test or not.



Apparently the new injectors didn't fix the problem. When my friend test drove the truck he could get the rpms above 2100 or speed above 55 when pulling a 3K trailer. He took a shop mechanic with him and the mechanic agreed there was still a problem. My friend asked me not to mention the shop's name since they are still working on his truck and trying to identify the cause of the problem.

 

[Johnstra]

If he really has low compression in one or more cylinders, all the fuel in the world isn't going to help him.



But... I wonder if his compression is really OK and maybe he's just not getting enough fuel. Could be governer related or a leaky AFC. Either of those could hold back fuel.



Could also be his injection pump is underfueling. I don't know how common a problem this is (I gather not very), but when I took my pump in for calibration I found out it was underfueling pretty badly. My truck used to stumble badly launching in 2nd, now it launches like a rocket.



-john

 

[McLaughlin]

I didn't mention it before but the shop replaced his injection pump (it was only 8 mon old so he was complaining about the short life of the pump) before the injectors so unless the new pump is bad that probably isn't the cause. My friend didn't mention if the shop had worked on his governer or AFC.



We seem to be think along the same lines as I was wondering about the AFC also. Next time I see my friend I'll ask him if the AFC has been checked. I'm also wondering if his catalytic converter could be somewhat clogged, since I've watched my friend idle his truck when cold for 10 or 15 minutes.

 

[Johnstra]

Wow! They replaced the pump!? I hope they gave him a good reason. The P7100 is very durable. Some do go bad, but it's rare and a good diesel injection shop can calibrate and even rebuild one if necessary.



The AFC and governor are part of the P7100 so if he has a new pump, it should be safe to rule those out.



Does his truck black smoke a lot? Is he getting good boost?



-john

 

[tp0d]

hmm sounds like theyre going after some of the wrong things. Hopefully they didnt charge him for the injectors if they didnt do anything to solve the problem.



Sounds like he has a lack of fueling. Things to do would be: change fuel filter, disassemble fuel heater/prefilter assembly, inspect+clean, and possibly get a gauge on the outlet side of his lift pump to check flowing fuel pressure. He could also have a restriction at the fuel pickup in the tank. Could mebe be an air problem at a rubber fuel line somewhere...



you only stated this was a 2nd gen. . Are we talking 24v or 12v?



good luck



-j

 

[McLaughlin]

John,



He isn't sure what boost he is running since he doesn't have guages. He had planned on putting them in until this problem occurred. He said he gets a lot of black smoke when it is cold.



tp0d



They charged him for the injectors but not the injector pump they put on right before replacing the injectors. The asked him before he picked it up if we wanted his old injectors in the truck or the new ones. They told him the new injectors wouldn't really cure the problem but would compensate enough that he should notice it when cold anymore. After he picked it up it still wasn't right so they are still looking at it, depending on what they find and the charges he may bring up the injectors as an issue since apparently they didn't correct the problem enough to make it driveable. I don't know if anyone has checked his fuel pressure or not. He is usually pretty anal regarding filter changes and the like so I'm pretty sure that isn't very old but then I don't think it has been changed since the problem began either.



He has a 12V.

 

[Johnstra]

Lots of black smoke and low power sounds like low boost. Wonder if he has a boost leak that goes away when the engine warms up. He can use regulated air pressure to look for boost leaks. Exhaust leak could rob boost too and to away when hot.

-john