Engine/Transmission (1994 - 1998) What Can it Be?

[Andy Redmond]

If it get stretched to much the lift pump may hammer at idle, due to fuel needing to be returned that is having difficulty with an overflow valve not opening soon enough. So calipers are a good idea.

 

[JJW_ND]

Pre boost adjustment!

I agree with Andy on the pre boost adjustment.



While trying to fine tune my GSK's and going through the top (remove AFC and plate) I backed off the pre boost screw. When I installed the spring kit a few years back I gave it an extra turn or so after making contact as this was talked about often at the time. When I went for a drive I NOTHING until near 2000 rpms. You could stand on it at 1400 and it would very slowly and calmly rev upto about 2000 and then take off like a rocket. No smoke down low either.



That little adjustment might also solve others poor starting issues. You can make the adjustment without removing the AFC.



jjw

ND

 

[Dave Remillard]

I'm not familiar enough with the pre-boost screw to confidently make an adjustment. Heck, from what has been explained, I know it resides on the back of the AFC, but wouldn't know it for sure unless I have more info. I think it's behind the cover that requires the removal of four screws to get to it. Is that the one that was used to adjust the diaphram when the AFC spring kit went in? Thanks

 

[Andy Redmond]

Yes, it can add a little spring tension on the diaphram.



The cover to which you are refering will allow access to the diaphram. The adjustment you want is the small cover attached to the cover for the diaphram? Am I making any sense?



It is attached with a short breakoff bolt which you might have swapped out for a socket head m6*10mm*1. 0 bolt and a flat bit machine screw with a very tall head.



Once inside the pre-boost screw takes a 3mm hex wrench and a 10 mm box combo wrench to loosen the lock nut.



Carefully count your turns so you can put it back where its at a later time.



Good luck. Andy

 

[Dave Remillard]

Thanks Andy. Yes, you made perfect sense. I did get home a little sooner today than normal so I checked the overflow valve spring. It was at . 043 so I stretched it to . 055. It did help in terms of smoother idle, and perhaps a wee bit on low end power, but I'm still not satisfied. I'm also curious if I should adjust the pre-boost. When I installed the AFC spring kit, I had the diaphram nut down to the point it was just touching. The truck ran awful, so I backed it off about two turns. I realize how delicate adjustments can be on these P7100 pumps, but can such a little adjustment on the pre-boost make that much difference. I hope to get home early again tomorrow, and if time allows, I will give the pre-boost a tweek.

 

[Andy Redmond]

I would back it off until it just touches. Then turn it in one full turn, if you don't see gray smoke emmision at idle and it performs well leave it alone. If two full turns don't get it (close to oe setting likely), then maybe lets call that enough.



If it runs well but smokes back it off a 1/2 turn and see what happens.



All it does is give you some fuel until it builds enough boost to start to overcome the diaphram and the strap can start up the cam plate for more fueling.



Also there is an "eccentric" at the front of the housing that has a M6 cap screw with a 10mm head that holds it down. It should usually be in the middle of the slot. If memory serves it the more its rotated towards the engine block will richen the mixture and away leans it out. The AFC is usually upside down in my vise when I adjust it, so maybe I've reversed what it does. With the capscrew loosened and the afc in your hand its easy to watch the link move up and down (raising or lowering it in the pump).



You are certain the gov. lever is correct right? You can hold the fuel shut off solenoid lever up with one hand and move the throttle with the other to see where it will contact (shouldn't try to go under the plate).





Good luck, Andy

 

[dseabaugh]

Been going through tthe same thing you are. Take out allen socket cap and spin the star wheel towards front of engine a few rounds. see if it runs like a striped ape then. mine will improve with every few turns; back it to the middle and it won't accelerate enough to pull out of the drive.

 

[Dave Remillard]

The following is a list of what I have checked and adjusted to date, but still haven't cured the problem. 1. Fuel pressure at 24lbs. in park and idle, 15 to 16 at WOT, and around 18 just cruiseing down the freeeway. 2. Grid heaters cycling. 3. Governor lever set correctly. 4. Replaced boost hose from intake manifold to AFC. 5. Measured overflow valve spring and stretched to . 055. 6. Star wheel turned in. 7. Fuel plate full forward. 8. AFC full forward. 9. And finally (if done correctly) adjusted the pre-boost screw. Alot of very good ideas from all of you, so just want to thank you all again. I've had a talk with Al at Piers Diesel, and he is going to try and help also to come up with an idea that may cure this. Again, thanks to each of you.

Dave

 

[Berrigan]

Let us know what you come up with!!!

 

[Deezul1]

Dang, after all you have done and checked there cant be anything wrong with it. Boy you have me stumped.

Good luck finding it

John

 

[TKemper]

Sixshooter, I don't recall if you said or not, but which AFC spring did you put in? I would pull the AFC back off. Make sure the star wheel is bottomed, ( all the way forward ) then turn in like 2 to 3 clicks. Should be plenty smokey, but should return your low end boost. Also like Andy R. said check the pre boost adj. Before making any adjustments, I would pull the diaphragm cover and check it for holes, or try a vacuum tester, apply 5 to 10 in of vac and see if it leaks down. A pin hole in the diaphragm might be hard to see. With the AFC out and in a vise, turn the pre boost Allen screw counter-clock wise until it's almost out. Now start turning it back in while watching the AFC link. As soon as you see the link begin to move you should also feel the allen screw gain a little tension. Now mark the screw and turn in 1 to 1 1/2 turns. I might even go 2 turns for test purposes. Now that you visually made the adj. put it back together. Make sure when you bolt the AFC back to the pump that it seems centered between the #10 plate, you don't want the side of the link to rub on the side of the plate, it might hang up a little under low boost. Don't forget to hook up the AFC boost line and take her for a spin. If your low end is better ( and it should be ) now you can fine tune it. Check the exhaust at idle, if it's too smokey turn the pre boost screw out a 1/4 to a 1/2 turn and check. I have mine turned in 1 1/2 and I have a light gray haze at idle. Now while driving check smoke at low to mid boost. You should be seeing black smoke the way your set. If you want less smoke, turn the star wheel away from the engine. Only do 1 click at a time and retest. I found that once I got close to acceptable smoke ( for me ) that one click in either direction made a big difference. One click too tight ( away from engine ) and it was slow too boost, one click too loose and it smoked more than I wanted. Hope this helps ya! I really think your trouble lies with the AFC, I would recheck it. Todd

 

[Dave Remillard]

I had another round at trying to solve this yesterday without success. Bob Verhoef who belongs to the TDR and NW Bombers came over to provide technical support and a second set of eyes to confirm I haven't made an error. Thanks Bob, it's much appreciated. We concentrated on the AFC housing and settings. The AFC spring kit was re-installed according to TST's directions and the pre-boost screw set according to TKemper and Andy Redmonds suggestion, none of which made a difference. The diaphram was tested, re-checked the governor lever setting, so on and so on. Finally we decided to remove the #10 plate to see what would happen. Without the plate in, the rig almost had enough power to crawl out of the shop. It would in no way be driveable on public streets. Also when I put the rig in drive, the rpm's took about a 400 rpm dive.

Bob noticed that the keeper on top of the 3K GSK was flush with the top of the bolt. We tightened the springs up two clicks to see if that would change anything. The only thing it changed was move the point from the 1500 to about 1750 before the fueling came on and the thing would run like it should and of course the rpms at idle went up. Bob is going to stop by Wednesday and we will check timing. We doubt this is the problem, but not being experts, we think it will all least eliminate one other possibility.

I didn't pay alot of attention to posts about removing the plate, but the impression I got was that at least you could drive the rig. I suppose one other thing to try would be to swap out AFC housings and see if that helps. At any rate, I wanted to keep those of you that have offered suggestions updated. If another thought comes to mind, I certainly would welcome them. .

 

[Dave Remillard]

Bob came by yesterday and we took the AFC from his 97 and installed it on mine. No more problem. We then decided to take each one apart side by side to find any differences. Bob noted that it took much more finger pressure to move the rack on mine than it did on his. To make a long story short, we found that the heavy spring from the AFC spring kit was installed instead of the lite one. We also noted that the pre-boost setting was three full turns out farther on mine than on Bob's. This was after already adjusting it in 2 full turns the other day. The result is a truck that goes good enough now that at full throttle when the transmission shifts, the rear tires break loose. I didn't install the governor spring kit originally so before I try to make any adjustments there, I need to call Piers to try and get a feel for how much of the post should be showing above the spring retainer. All that is left is some fine tuning on the plate and perhaps tweeking the pre-boost a bit more. Thanks for all the ideas. I learned a ton as a result of this.

 

[Berrigan]

Glad you found the problem

 

[Andy Redmond]

I've run the hvy spring in a 160, 175 and 180 hp pump. It will be a bit more doggy on the bottom end, but it can be overcome somewhat by afc adjustments. The customer wanted less smoke and his pump was set up on the high side.





However, I like the medium (the longer of the two springs) in the afc kit, which is the recommended spring for your application.



I also put the medium spring in a 215 pump earlier this week as it had your symtoms. I decided to ck. fuel psi and after a new overflow valve all was well.



On the GSK I see the range of . 035-. 065 with good results. I bet most of us would all get differing readings using the same set of calipers.