Engine/Transmission (1994 - 1998) Suburban has never ran right

[CumminsBurban]

12 Valve has never ran right

Ok, I'm not sure how long this will be but I am thinking it will be fairly long. Just wanted to post that up front. I have a '96 Suburban that I put a Cummins in. The engine is a 1997 12 valve with a 47RH transmission. My Sub is a 4x4 1/2 ton.



Here is my problem. I get about 15 mpg empty. Doesn't matter whether I'm in town or on a trip. I have 3. 54 gears. When it is cold, it will lope at idle. If I put it in gear, it lopes so bad sometimes it will die. I first started driving with it stock. I had the same problem. I now have 300 HP injectors, a 4" exhaust, and the fuel plate modified. I have governor springs that allow me about 3,600 rpms. I can hit 35 pounds of boost in neutral. Also, it starts popping out the exhaust. If I am at an idle, and floor it in neutral, it is not a smooth revving. It starts popping when it hits about 2,000 rpm. My pyro is pre-turbo. I can peg it anytime I want and it measured 1600. It scared me when it happened the first time and I try not to do that anymore. My dad has a Cummins and my brother has a Suburban that he put a Cummins in. They both have are 12 valves, ''94 - '98. They both have more power than I have. They neither one get near as hot as mine gets. My timing is set about 17 degrees. Nothing I have ever done has changed the situation. Stock, it would still run hot. I pull a 38' bumper pull camper. I have the power to pull it but I have to be careful because I get to hot. I run about 40 pounds of boost and when I'm pulling @ 65, I'm constantly running 20 - 30 pounds on flat roads. I pulled it with Dad's truck the other day and couldn't believe the difference. He had probably twice the takeoff power I have in my Sub, and less boost and EGT's. This one really has us stumped. I called a tech line (who will remain nameless because I don't want to cause any situation) and the guy basically called me a liar when I told him I could rev my engine in neutral and hit over 30 pounds of boost. The engine has about 200,000 miles on it. Oh, another thing, my accelerator is much harder to push down when the engine is not running than when it is running. In fact, you almost can't push it down if the engine is not running.



Ok, I'm going to list some of the things that I thought it was or still think it is and hope someone can give me some direction.



1. Too small delivery valves - doesn't make sense because it did these things stock as well. NOw, the engine was from an automatic so I can see that could have caused a problem if the problem only came when we put the large injectors in.

2. Too small exhaust - my original exhaust was 3". Ok, I just put 4" on and didn't change a thing. In fact, I think fuel mileage dropped just a little.

3. Bad injectors - no change when we went from stock injectors to 300 HP injectors.

4. Timing is off - We have checked the timing 3 times. Maybe it is slipping but three times and the same result all three times. I struggle with that.

5. Air cleaner causing a problem - not going to cause it to lope at idle, and I took it clear out and no difference.

6. valve springs - we put the 4,000 springs in and no change.

7. injector pump - This is what I'm wondering about now but have never heard of one going out like this.



Any other ideas that you think may help, please let me know. I'm sure I have tried other things but I can't think of any more right now. It is really frustrating to me that I have higher egt's than my dad, higher boost, and he flat walks off on me. I always thought my Sub pulled my camper pretty good until I pulled it with Dad's truck. Now, I'm sick.



Thanks in advance.

 

[PorterS]

No expert, but it sounds like timing to me if you can hit 30psi in neutral. The popping also sounds like it could be timing related...

 

[Msilbernagel]

Since he's checked timing ( a mechanical means, right? ) perhaps it's the pump itself?



I've got a 93 Sub with an 04. 5 Unit and am consistently getting 18. 5-19MPG in mixed driving (rural). That's with a 6-speed and 4. 10 rear-end ratio.



Mark

-

No expert, but it sounds like timing to me if you can hit 30psi in neutral. The popping also sounds like it could be timing related...

 

[JoshPeters]

How did you set your timing? If you used the timing pin below the pump, I'd be willing to bet it's off.



Use the Dropped Valve method. Pull the number 1 valve cover, use the intake valve, and turn the adjustment screw in 3 turns. Roll the engine over slowly till it touches. Mark the balancer. Back the engine off, back the valve off... . roll it over PAST TDC. Drop the valve the 3 turns again. Roll the engine backwards till it touches. Again mark the balancer. Set your valve lash. Measure half way between the 2 marks and that is true TDC.



I set mine with the pin at 16* then I went back and used the dropped valve method and was off by 7 degrees! (actually 9* of timing) My truck had the popping and white smoke when I free reved it.



I'd definatly start there.



Otherwise... . Your engine and mine are in the same boat..... When I've gone to IRP in a group, I'm always the first one to need fuel. I run more boost and higher EGT's than everyone else in the group. NONE of us can figure out why. 2 of the other trucks are owners of Diesel Performance shops.



Josh

 

[tp0d]

I`d have to vote timing also, have you had someone else validate you really are at 17degrees, or have you always used the same method? Could be a flaw in what you're doing.



What fuel plate do you have in there? You just stated 'modified'. For an auto, a #10 does real well. Does the plate curve look like a half moon at all?



You put in 4k springs and no change at all with the lope? hmm strange. . have you done any fuel pressure testing for fuel delivery?



my go pedal is also hard to push when the engine is off. I believe this has something to do with the gov stopped and/or the fuel shutoff disabled...



good luck



-j

 

[Champane Flight]

I am

I am betting on the pump. I think maybe something is bound up, slipped, or missing. Arm falling under plate? Governor springs in wrong?

 

[Joe G.]

After reading all this I think it's time to go to an injection shop and get the pump checked on a test stand.

 

[Howard Durand]

It would appear that it is overfueling excessively. If the accelerator is hard when the engine is not running wouldn't that indicate backpressure from the pump? What happens if there is no return for excess fuel? Is the overflow valve working?

 

[Dieselnut59]

I think all the 12 valve p-pump engines are harder to mash the throttle when the engine is stopped. All the ones I have ever experienced are that way. Not sure why that is an issue. What good is it to mash the throttle on a diesel without the engine running? I believe (as someone else mentioned) that it is the governor causing that.

In my opinion, it sounds like you have a pump problem causing irregular fuel delivery.

 

[Joe G.]

I don't think it is overfueling. Be a lot of black smoke if that were the case. The popping would make me think that something in the pump is causing uneven injection. It was doing this when it was stock if I read the above problem description correctly. I wonder if there is some problem with exhaust valves. If it is firing late on some cylinders that would explain the high boost and the popping. I would think that firing late would cause more pressure in the exhaust thus more boost without making much power. Maybe really retarded timing. I wonder if sticking plungers in the pump would cause something like this. All of this is just guessing of course.



When the engine is stopped the pedal is harder to push because of the governor. How much harder is bad may be a matter of opinion.

 

[CumminsBurban]

Thanks for all responses. I will try to answer all additional questions in this post. I have been present all three times we timed it. My dad is a diesel mechanic. The first time it was timed was by his ear. My dad lives 100 miles away. I have a friend who lives close to me. We checked it with the tools and used the valve hitting the piston method. It was right on. My dad bought the timing tools and we checked it again. It was right there.



We have also adjusted the valves. They were not off much at all. I saw no difference when we adjusted them.



The reason I think the accelerator being hard with the engine off is an issue is because in my family, there are 5 12 valve Cummins. Mine is the only one that is substantially harder than the others. There is some difference in the others but not near the difference in mine.



I do blow lots of black smoke. No question I have it overfueling but I do not blow any more smoke than the other 4 cummins in my family.



After reading all of this, I am leaning real strong toward the pump. How much does it typically cost to put a pump on a stand and have it tested?



I do have a custom made fuel plate but I know that is not the problem because the other 4 cummins I know also have custom fuel plates. I am probably going to have my pump tested. I just want to find a place that I know will do a good job.

 

[HoleshotHolset]

Have you checked (and re-checked... ) all of your fuel lines? A little bit of air introduced into the fuel system will cause poor fuel economy, low performance, popping under high RPM/no load, or all of the above.



Since this is a conversion - you've got some homework to do in terms of making sure everything is right with the fuel delivery system. I've had hose clamps I thought were plenty tight cause air to get into the system... re-check 'em all.



Matt

 

[RoadGoesOnForever]

Pretty sure it is your timing. The symptoms you describe are exactly like me and lots of others witness when the timing is retarded. It is either not being checked/set right, or maybe you are not using the right plunger lift/timing chart for your CPL.

 

[CumminsBurban]

If it is the timing, it is something internal to the pump causing the timing. Both mechanics who helped me with the timing, my dad and a friend, have timed many 12 valves and have never had a problem. I can't see a problem that they have never had while timing a 12 valve, would happen three times in a row on my vehicle.



I have checked fuel lines but just before I take the pump off, I will recheck them all again.



At least it is nice weather so I can let my wife have my suv while I take her Suburban out of commission and I can ride the Valkyrie.



Even though it is not running right, my wife loves it. The only time I drive theSuburban is when I beg or she is with me. I even offered to buy her a newer gas suburban with heated seats and all that. She said I better not even think about it.

 

[JoshPeters]

The first time it was timed was by his ear. My dad lives 100 miles away. I have a friend who lives close to me. We checked it with the tools and used the valve hitting the piston method. It was right on. My dad bought the timing tools and we checked it again. It was right there.

Now I don't mean to offend you, your father or anyone else, but "timing by ear" on these engines isn't really possible. Sure you can hear timing when someone is very retarded or advanced, but this isn't an old chevy where you can twist the distributor and change it to hear the difference.



The Dropped valve method if done correctly is right on the money. (I did exactly that, and just pulled the head, mine was EXACT with a dial indicator on the top of the piston)



I'm with Holeshot on the timing chart idea. If you don't have the correct CPL, your timing could be off by a ton!



When you set the timing what are you setting it to? What is your CPL and how many MM of lift are you setting it to?



Josh

 

[CumminsBurban]

Now I don't mean to offend you, your father or anyone else, but "timing by ear" on these engines isn't really possible. Sure you can hear timing when someone is very retarded or advanced, but this isn't an old chevy where you can twist the distributor and change it to hear the difference.



The Dropped valve method if done correctly is right on the money. (I did exactly that, and just pulled the head, mine was EXACT with a dial indicator on the top of the piston)



I'm with Holeshot on the timing chart idea. If you don't have the correct CPL, your timing could be off by a ton!



When you set the timing what are you setting it to? What is your CPL and how many MM of lift are you setting it to?



Josh

Josh,



No offense taken but you're wrong about my dad. He has a method and a God-given talent. He was the first to time it by ear. Granted, he may not always get it to the exact degree but the vehicles he times always run better when they leave his shop than when they come in to the shop. Now that he has the dial indicator setup, he doesn't time these by ear anymore but he is effective at it none-the-less. The other two times we timed it were with the dropped valve method and the timing was where we wanted it to begin with. so, maybe Dad got lucky but he sure gets lucky an awful lot. We set the timing @ 17 degrees if I remember right. I don't remember my cpl and how many mm of lift because it has been a year since we did it, but we went through all the procedures. Both my dad, and the friend who helped me do this for a living. They both have timed many trucks. There is simply no question in my mind that it is not actual timing. I am leaning more every day to the possibility of something in the pump causing the timing issue but I do not believe it is the actual timing of the gear.

 

[JoshPeters]

If it was a year ago, the timing may have slipped. I check mine every 6 months or so. Usually in that time it's dropped a degree or 2. I use a new lock washer every time too.



From what I know about the P-7100 there is nothing inside that pump that does any kind of timing.

 

[Extreme1]

If the pump timing has been set accurately 3 times with no changes it's time to look at something else. The high boost in neutral ain't right, something is FUBAR somewhere and being the "experts" that we are we should be able to find it.



I'm guessing that you got this motor used and never drove it before the swap? If that is the case I'd be suspect of everything. Confirm the pump part number with the CPL # you used, someone might have changed parts on you.



Something else I'd check is the cam. Throw a dial indicator on the rockers and compare them to each other to make sure they are the same (Intake and exhaust will be different from each other but each group should all be real close).



If that looks good, try a compression test. You'll need to hook up a compression tester to an old injector body, pull them all out and test one at a time.



Then on to the pump! Pull it and send it to someone good (PDR, etc. ). I had a local shop that does tractor puller pumps set up a 180 hp pump and PDR set up a 913 for twins. The PDR pump is WAY faster and gets better milage. It's worth the freight!



Good luck and keep us updated!

 

[DonFitzwater]

Cumminsburban, make sure that you post what you find when your problem is figured out. I have talked to lots of people about your problem here in Alaska and everyone thinks it is your pump. I would really like to hear what it is.

 

[CumminsBurban]

If the pump timing has been set accurately 3 times with no changes it's time to look at something else. The high boost in neutral ain't right, something is FUBAR somewhere and being the "experts" that we are we should be able to find it.



I'm guessing that you got this motor used and never drove it before the swap? If that is the case I'd be suspect of everything. Confirm the pump part number with the CPL # you used, someone might have changed parts on you.



Something else I'd check is the cam. Throw a dial indicator on the rockers and compare them to each other to make sure they are the same (Intake and exhaust will be different from each other but each group should all be real close).



If that looks good, try a compression test. You'll need to hook up a compression tester to an old injector body, pull them all out and test one at a time.



Then on to the pump! Pull it and send it to someone good (PDR, etc. ). I had a local shop that does tractor puller pumps set up a 180 hp pump and PDR set up a 913 for twins. The PDR pump is WAY faster and gets better milage. It's worth the freight!



Good luck and keep us updated!

We never drove it before the conversion. I got it out of a wrecked truck. the entire engine had battery acid all over it. We have checked the cpl number and we're ok there. Checking the cam is not a bad idea. My question there is wouldn't that cause other problems as well? When I am under a hard load, there is no miss or lope. It is steady. It is only at an idle that there is a lope.



For compression, I have not checked actual compression numbers but if you disconnect the fuel sylenoid so you can turn it over, it is very even.



I'm leaning toward sending my pump to Scheid, simply because we are not too far. I actually have talked with Haisley a little because I am only about 15 miles from them. They recommend sending it to Scheid.



I would like for some of you to verify something. You that have 3k or 4k Gov springs, check your vehicle in neutral and see what boost is @ 3k, and at 3. 5k.



Thanks and I will keep you all posted. I am a little short on money now so if it is the pump, it may take a little bit before I get it fixed, but we are supposed to pull our 38' camper to the Smokies in August and I will not pull it until the problem is fixed.



Shane