All Is Not Well With 370s

[Believer]

Installed 370s in my 94. It had previously had the pump changed to a 180 pump although I'm not sure of the delivery valves in it. Well, it really jumps now but with a load of 3500 lbs in the bed I get a surging or bucking at half pedal in 4th at about 1700 rpm. If I give more fuel, surging goes away and of course less fuel solves problem. Once I get through to about 2000rpm, it seems fine. Does not do this with no load in the bed. I don't have the 1100 rpm stumble reported with too small delivery valves. Any ideas?

 

[John L]

Believer-

I have the same problem with my 97 (cal model). When the rpm's reach 1750-1900 my truck stumbles or surges. This happens at normal driving and not WOT. I thought I could solve the issue by installing the larger (191?) delivery valves but it didn't help. I emailed both Piers & Tst but they haven't responsed yet.

I'm thinking maybe the cam profile of my TST #6 plate doesn't like the 3K governor springs? I don't know... . Hopefully someone can help both of us.



John

 

[Dave Remillard]

I'm having the same problem with my 95 with 215's, only at 1000 to 1200 rpm's. I also have not gotten a response from Piers. Unusual, but true.

 

[HoleshotHolset]

If you want to talk to Piers... . call him. 604-888-4159

I've spoken with many vendors, and it's really hard for them to keep up with 90+ emails a day... .



HTH,

Matt

 

[MDW]

Have all of you checked your fuel pressure at the given rpm that is giving you the problem? Install a guage, put it under your windshield wiper and go for a drive or however you can acomplish this.

The only thing I can think of to cause surging like you are describing is surging fuel, the things that come to mind is the govener, lift pump, overflow valve, good luck.

 

[Strick-9]

My experiences.



I've been down this road. My truck has always slightly stumbled. I bought the governor spring kit and 191 DV's. It stumbles with both stock 160 injectors as well as the 370's.



What I've found is that the stumbling always occurs just as the flyweights are coming onto the lower spring seat in your governor spring kit.



Everybody sells a different lower spring seat. The flat bottomed seats allow more flyweight travel thus more rpm before they hit. The deeply recessed seats hit early 1000-1200 rpm. This can be manipulated around to each individuals driving habits to minimize the problem.



I made some custom spring seats that had huge recesses cut into them. I could blip the throttle while idling and make it stumble continuously at idle.



For those of you not willing to change out your spring seats or without access to more, you can change the preload on your retainer nut. Tightening them will make the stumble occur at a slightly higher RPM, but also makes the transition from the idle spring to the spring pack more pronounced. Loosening the nut makes the transition less pronounced so the truck will be slightly less prone to stumbling, and makes it occur at a lower rpm.



I'm running a set of staged springs right now to eliminate the hard transition in spring stiffness as the flyweights expand onto the spring pack seats and the stumble is gone.



There were days when I was installed 10 different sets of governor spring combinations a day to try and find the source of this stumbling problem. Maybe the information I learned will help someone else.



-Chris

 

[HoleshotHolset]

Good info Chris!



Matt

 

[John L]

Hey Chris-

Thanks for the info... Sounds like I can't really do anything to eliminate the surge/stumble without allot of R&D. I can just move the surge/stumble alittle higher or lower in the RPM range?



John

 

[HEMI®Dart]

Good Eye Chris

 

[Sled Puller]

I too fooled with those pesky springs, tight, loose, tight, loose.

Did not help.



Changed the overflow valve, seems to be gone. Need more time, around town as I have been testing mostly at WOT today.





180 pump,191 D valves, then Laser cuts, 4000gspk, 370 inj, Piers race plate.

 

[drawson]

I have been dealing with a similiar problem, I could actually hear the turbo flutter and watch the boost gauge flutter. This problem started with the 370 injectors but has moved right along with the additions of the governer spring kit and the HX-40.



I made a plate to take the place of the AFC housing to seal off the hole in the top of the injection pump and ran w/o the AFC and the flutter is gone. And let me tell you she smoke now big time before boost comes on, day becomes nite:--)



I think what is going on in my case the AFC spring is just starting to pull back and adding fuel and then it pop forward just a tad and with these big injectors they cause a surge. Some here are running w/o the lever in there AFC housing, but I for one need it so that my Valet kit works. have a spared AFC housing and I'm going to reshape the lever to see if I can get rid of this flutter.

 

[Deezul1]

I also have a surging at 1700-1800 rpm in 3rd gear only that started after installing 4k GSK. It is a lot better after loosening the spring adjustment on the governor spring retainers but is still there a little. The really wierd thing is it got better after replacing a puck on one side type clutch with a Southbend Con-O, who knows why but it did.