Bucking and carrying on , something injection related
 

My buddy just bought a 95 Cummins 4x4 5spd today, it has 300k on it, Supposedly has timing advanced 19* i think the guy said? and 60hp Injectors, and a #10 Plate. Pulls Okay but at like 1200ish rpm if you make normal shift into 4th or if you get in that RPM neighborhood at all and keep your foot steady it starts bucking and running crazy like it shakes the whole truck and it feels like a miss, but you can squeeze the pedal and power through it, sounds like a sled pull truck does when they are bringing up RPM's when they're running choppy

The #1 Injection line coming out of the P7100 is leaking for sure, not sure if it's the actual line though or where the delivery valve holder attaches to the pump itself. sorry i don't know any terms to do with the p7100,

It's one of 4 things in my opinion

- Fuel filter
- Fuel leak at injection pump causing the issue
- Timing may be too advanced or even retarded?
- Bad injector(s)

I'm leaning more towards the last 2 though, doubt a fuel filter would let it run good in the higher rpm's but make it run rough in one tiny little spot. And if it was sucking air it seems like it'd run poorly all around....It idles perfect and you can rev it up in Neutral and it's fine, but driving it in low rpm's is when it does it. even if you take off in 2nd it does it for a quick second before you give it more pedal

VIDEO--




Thanks
Brandon

Oh and if anyone knows the truck it's all Charcoal Ext. cab LWB from Bordentown, NJ . Figured he had to be around on forums or something to be up on the pump and what not

Interesting...I would check what you mentioned..Pull the injectors get them tested,reduce timing to 15 degrees,check the shutoff that its not cutting in and out...Maybe even a external fuel fuel pressure gauge to see what the pressure is doing when the engine starts to sputter...

I've gone through all these tests when I was having a problems with a intermittent highway shutoff on my truck..I did all the basics and couldn't find the problem...The only fix was when I replaced the IP...something was screwed up inside..But don't replace the IP just yet...Maybe a sticky barrel on the IP???

Brandon,

It sounds almost exactly like a buddy's 95 truck when he had 370 marine injectors in it. Like your buddy's it would only do it at certain RPM. The marine injectors don't have the correct spray pattern.

Ok so i think fixing inj. leak and putting diff. injectors in it is a good start

What are decent running decently priced injectors for these? Bosch 230's ?

And a good place to buy them.

Truck has stock turbo and stock intercooler. EGT/Boost guages

I will throw this out there, for consideration. My 94 has an auto, and does that. Mine does it because the tranmission shifts into torque lockup too early- the RPM's are so low when it does it, that due to the torque, I am feeling it hit on each cylinder. Shakes the truck like crazy- it got worse when I put 75 horse injectors in. There is a service bulletin on it, to replace the PCM with a new one, programmed to shift at a higher RPM. Saying all of this, I bet you wouldn't deal with it if you shift at a little higher speed/RPM. What are you reading on the tach when you go into 4th? Pretty low RPM's? It sounds like a similar condition. Mine will power out of it, too, or I just hit the O/D off button. That's cheaper ($600 for the PCM/reprogram).

Opps...I didn't read that it had non stock injectors...[duhhh]

There's no way to avoid it. Anytime it goes in that 1000-1200 range it starts bucking even if you leave a stop sign regularly in 2nd gear, then shift to 3rd and give it normal acceleration then you'll feel it.

You HAVE to power through every gear and wind it up because if you hold the pedal steady it will do it.

Nothing wrong with your IP. A turned up IP with larger inj's are going to do this every time at that low of rpm. You aren't doing anything good for the engine or fuel mileage to run below 1600rpm anyways, so re-learn to stay above this rpm and problem solved.

I've never had this with any of my trucks, with injectors ranging from stock to 250+, 12 and 13mm pumps. There is something else at play. If its makes that noise leaving a stop sign in 2nd, there is issues.

Get a fuel pressure gauge on it first. Get your leak taken care of. Then I'd have your injectors tested. See what happens there. A cleaned or new set of injectors may be the cure, but have them tested first, unless he wants to upgrade anyway.

Tate,
I believe he is trying to drive (keeping a constant rate of 1200rpm) not drive through that rpm when leaving a light or stop sign. He mentioned
"Pulls Okay but at like 1200ish rpm if you make normal shift into 4th or if you get in that RPM neighborhood at all and keep your foot steady it starts bucking and running crazy like it shakes the whole truck and it feels like a miss, but you can squeeze the pedal and power through it, sounds like a sled pull truck does when they are bringing up RPM's when they're running choppy"
The higher the gear the more pronounced it will be. You won't feel it in 1st or 2nd and in some cases not even in 3rd.
This is normal for any pump that has been turned up to flow allot of fuel, but only at very low rpm holding steady. At idle the rack rests on the pre-advance adjustment. Come just off this with a load on and it will bounce. Give more or less throttle and the transition of the rack and gov will make it go away.

I've found that to be exact opposite. My 13mm in my dually, in anything below 4th and 5th, trying to hold at a steady state will induce the bucking of an overly sensitive pump. 4th it can be controlled better, 5th better yet. And its through out the entire rpm, not just the lower range. The fact that it only has advanced timing and 60 hp injectors also leads me to believe it is something else. A built pump, or even one with 4k's and big DV's, I can see it bucking. I'm in that boat now with my 12v. But again, lower gears only, and the whole rpm range is affected.

I can guarantee it's not a "built" injection pump, if so, it's a sad one. This truck runs good don't get me wrong but it falls flat on it's face a little under 3000 and kinda feels like it's dragging something about 80 mph (it just starts to get slower and not pulling much at all)

I went to buy the truck with him and the guy barely knew anything, he said the "ACF" was turned and had 60hp injectors. the egt's max about 1400-1500 if you stay in it for a while, and boost is like 32 lbs MAX

We did verify last night though it's a #0 plate and not a #10 plate like he said........

What little i could see with the fuel plate out, everything looks okay. Fuel plate is definely a zero though. LOL

I have the same problem as Tate with my truck right now, which happens to be a 95 engine with a worked over 160 pump. Over sensitive throttle that will start bucking, towing is almost impossible.

Brandon,
Like I said before I went through this with a friend's 95. He put bigger injectors in, 370 marine injectors to be exact. Wouldn't run right, ended up installing 191 delivery valves. Had the exact same thing around 1200 rpm. We ended up having 215 hp tips installed on his stock injectors. Never did it after we installed those.

If you have a over sensitive throttle, then your pump isn't set up right. Even when a ran my 13mm stupid pump, I could tow, drive around town slowly or rip up the hwy and be smooth. My 12mm pump now puts out almost as much as my old stupid pump and i have no issues driving in 1st, 2nd or in most cases 3rd at any rpm, including 1200rpm. As mentioned 4th, 5th or 6th I could make it buck at 1200 due to gear ratio/load but why would anyone want to be at that rpm in those gears anyways. At any rpm above 1200 in the higher gears, it's as smooth a glass.

I have driven and worked on hundreds of trucks at PDR over the years and have heard Brandon's bucking complaint from many customers. I jump in the trucks and take it for a drive with the customer and it drives just fine, no bucking what's so ever. The typical responce from the customer is but if you drive at 1200rpm it bucks? These engines aren't made to have a load on the engine at that kind of rpm. The lower the gear, the less load on the engine. If you are have bucking issues in a low gear, then your pump isn't set up correctly. Simple as that.