Engine/Transmission (1994 - 1998) Slight stumbling after new modifications

[JSpeh]

Just got finished installing 370s, 191s, Ats intake and bumping my timing up to 15 degrees. Got the truck running and noticed a stumbling problem in the 1,000 to 1,250 rpm range. If you get down on the throttle it does fine, when you ease into it at that rpm, it will start stumbling and jerking the truck. Truck seems to run great as long as its not in that rpm range. Not sure if I should make some adjustments to the #6 fuel plate or not. As I recall, the plate is in the stock location but I think I set the AFC housing all the way forward. Any advise from you guys would be greatly appreciated. Thanks in advance!



John

 

[JSpeh]

Could I still have some air in the injection lines? I don't see any leakage on the high pressure side. I bled the lines a little again yesterday, seemed to get a little better for a while. I will try bleeding the lines some more when I get home from work today. You can hear the stumbling (missing) a very little bit while idling, didn't notice it the other day.

 

[DonFitzwater]

I'd have to say to start with the basics... ... check your fuel pressure and rule out your lift pump and overflow valve.

 

[JacobsD]

There was a thread about this a while ago, the 160 and 175 pumps seem to have a studder at that RPM that is just magnified with fueling mods. Mine does it and its making me closer and closer to buying a 215 pump...

 

[CBeeman]

more timing???

 

[hdm48]

Mine was doing the same thing until I changed the overflow valve. When I pulled out the old one I could see junk through the holes. But I picked up the "new and improved" valve from DDP and now it runs smooth again.

 

[JWashburn]

Its probably the injectors. Do a search on the 370 stumble. If its the "370 stumble" it will go away after warm up. The 191s supposedly fix some of that, but I was never convinced enough to try it.

 

[JFaughn]

You sig does not say what trans you have , but since it mentions a gauge , I assume an auto ,
I got what may be the same symptom , a little less it sounds like because of less fuel , a vibration/shutter at around 1,250 RPM , just enough throttle to maintain speed , around 35-45 mph , after OD & lock up , if I hit the button that turns off lockup , it goes away , but not sure because it raises the RPM above the 1,250 ,
My guess is it will go away when I build the trans ,
If your adding that much fuel , you should be saving up for a built trans .
The bottom line is I think that as the low idle , the trans pressures are not high enough to keep the lockup from slipping .

 

[ddechris]

Been struggling with the same thing with my 300 injectors. Mine is in the 1200-1500 range. I installed a borrowed set of laser cut delivery valves and 1200-1500 is smooth, but there is a harsher shudder from 1000-1100. I ordered a set from TST and I'm hoping they are somewhere between the two.

 

[Bloomy]

I never had the stumble with the 370's, but I made sure to install the 191's before hand since the stock 131's would almost guarantee a stumble. Do you have a gsk of any variety?



Thomas

 

[JSpeh]

I did install a new overflow valve when I installed the other mods. After the stumbling started, I reinstalled the old overflow valve to see what happened. The stumbling seemed to have gotten quite a bit worse. My old overflow valve was definately weak. I do have a 3k gsk but I have not installed it yet. I just put a new lift pump on the truck about two years ago, so that should be functioning ok. I'm definately not expecting the transmission to last very long with these mods. She's a ticking time bomb! I'm a little hesitant to go past 16 on the timing, though. Anybody have any ideas/experience on how much a 215 p7100 pump would cost and where's a good place to get it from. I'm leaning towards the injection pump causing the problem. Thanks again for the advise and suggestions guys. I'll keep trying other things in the mean time. Maybe moving the fuel plate all the way forward will help.

 

[Driftwood Ram]

Did this ever get resolved and if so, what was the fix??

Thanks,

Tracy

 

[Vaughn MacKenzie]

This sort of miss/stumble is common on 12-valves, happens to 215-pump trucks a lot too. Sometimes new overflow valves, GSK spring adjustment, different delivery valves, timing adjustment, injector replacement, etc. will clear it up. In my case with my '96 none of those worked, then went to doing compression checks, valve job, new injection pump, 2 sets of injectors all to no avail. The miss lessened when I put in a set of DDP stage IIs and now it's tolerable. There's a few instances like mine where curing the miss is mission impossible, it's a "12 valve thing. "

 

[Driftwood Ram]

Vaughn,

I was just trying to see if the original posted found a solution. I have followed with interest your trials on the NW Bomber site.

I am just tired of living with it. Had the shudder or whatever you want to call it at the 50-55 mph range for years and have learned to drive around it. The Smart Controller kicks it out of OD at about 55 and I just manually use the OD button on acceleration after the speed gets over 55. Now after adding DDP II's and a 10 plate it shudders at 35 too.

I would like a truck with 6 wheels to better be matched to the weight I tow, but the way this is running right now, I can’t even think about letting someone take it for a test drive. I guess I will have to wait until we get back up North.

 

[JAmos]

What rpms is the shudder occuring at? My dads 95 auto-bone stock-had the shudder. It seemed to be lugging and as soon as ya mashed the throttle or kicked it out of od causing the rpms to go up, then it was fine. It acted like it was shifting into od too soon(about 35 mph and i'm guessing 1100-1200 rpms) and lugging the engine. He also had torque converter lockup issues, but had someone work on it and think his problems are gone.



Jordan

 

[Driftwood Ram]

You got it, 1200-1300 rpm. 35 mph is where it locks in 3rd and 50 mph is where it locks in OD. Unfortunately 35 mph seems to be a favorite speed limit around town.

Piers is going to work on it for me when we get back up North next year. I was just trying to see what others had found.

 

[JAmos]

Both of my manuals shudder a little occaionally at low rpms in 5th, I usually downshift to 4th incase i want to punch it. 4th puts the engine at higher rpms where the turbo lights quick. I like the theory that the tps, vss, pcm, and valve body should work together to keep the rpms up to prevent this problem. This way by better utilizing throttle position data, the pcm and valve body can know when the truck is idling through town and the rpms should be higher to prevent the shudder. When the throttle is mashed and the truck won't shudder, the transmission can/should shift at lower rpms to take advantage of the torque curve. I'm not nessecarily a transmission expert but this is my theory.



Jordan

 

[JSpeh]

Hey guys, what I ended up doing was putting the original injectors back in and leaving the 191 delivery valves in place. This solved the engine miss. I know that it was the bigger injectors that amplified the problem. Not sure if it is the injector pump or something else. I did check my fuel pressure and that seemed to be OK. I do still have the 3k spring kit but I still haven't had the time to install it. Maybe I can get that done next spring since I don't have a garage to work in. Weather is starting to get undesirable for vehicle repairs. I would still like to bump up the timing a little bit more as well. I'm at about 15 BTDC right now, might go to about 16. 5 BTDC.

 

[okayred]

Mine does the same thing - I posted it a few months ago "engine shudder at low RPM". Right after I put a new clutch in, it stopped... for about a week. Then right back to the same thing. You can see by my signature what i have in the truck. I'm afraid that from all I've read, Vaughn MacKenzie is right... you might get lucky with the right combo and eliminate it.



I'm gonna keep working on mine & I'll re-post if I gitter fixed!

 

[JAmos]

Is there any possibilities that the stumbling could be coming from missmatched injectors-as in not perfectly matched and having slightly different "pop" pressures?