12v Lift Pump Pressure? VIDEO INSIDE

1

1slowhatch

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Jul 6, 2009
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Been chasing a low rpm miss/shudder problem for a while now.
'95 12v 5 speed, 120k miles, 3k gsk, 4 inch exhaust, 5x.014 SDX injectors, etc etc.

The truck is really jerky under 1500 rpms, and gets worse as the engine comes to temperature. I was told it may be a broken throttle spring. I put a spring on it, and it still does the same thing. It does it free revving and under a load, but idles pretty smooth.

I was told to look into a TSB regarding lift pump pressure and overflow valve. I installed a fuel pressure gauge by taping the banjo bolt into the injection pump (feed from the lift pump).

Here is the video (truck is idling and at full operating temperature):

[ame="http://s1218.photobucket.com/albums/dd420/1slowhatch3/?action=view&current=12vCummins012.mp4"]12vCummins012.mp4 video by 1slowhatch3 - Photobucket[/ame]


As you can see, it is very jumpy. The pressure is also lower than advised. I crimped the return line as advised in the Dodge TSB and the pressure instantly pegged the gauge. Another thing I've noticed is that my truck is continuing to idle lower and lower. I put the GSK last year, and it seemed to idle too high. Now it almost dies with the A/C on.

Should I put a new overflow valve on it? Is it a lift pump problem? Any input is greatly appreciated..
 
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Modify your stock overflow valve with a bic pen spring. Try to get 35-40 psi at idle and 40+ at 2500 rpm free rev.

As far as your idle, you can adjust your idle up with the idle adjustment screw but I would strongly advise you to tighten the governor springs 2 clicks on each side = 180* turn on the preload nut.
 
Big Blue24 said:
Modify your stock overflow valve with a bic pen spring. Try to get 35-40 psi at idle and 40+ at 2500 rpm free rev.

As far as your idle, you can adjust your idle up with the idle adjustment screw but I would strongly advise you to tighten the governor springs 2 clicks on each side = 180* turn on the preload nut.
Click to expand...

Thats what I was thinking. Im running between 35-40 psi at idle.
 
Big Blue24 said:
Modify your stock overflow valve with a bic pen spring. Try to get 35-40 psi at idle and 40+ at 2500 rpm free rev.

As far as your idle, you can adjust your idle up with the idle adjustment screw but I would strongly advise you to tighten the governor springs 2 clicks on each side = 180* turn on the preload nut.
Click to expand...

I don't suppose you have any info on how to modify it? Does it just need to be replaced?

Also, does it seem normal to be that jumpy on the gauge?
 
Big Blue24 said:
As far as your idle, you can adjust your idle up with the idle adjustment screw but I would strongly advise you to tighten the governor springs 2 clicks on each side = 180* turn on the preload nut.
Click to expand...

I did that on mine and it raised the idle to almost 1000 but would still stall when dropped into gear. I loosened them back up 2 clicks and adjusted the idle with the idle screw and I only had to raise it to 800 in neutral and it would drop into gear without stalling. I'm told tightening the governor springs tend to cause a "hang idle" but it didnt help my stalling at all.
 
1slowhatch, it is fairly common for p-pump rigs to have a slight miss on one cylinder at partial throttle between about 1200-1400 RPM. Guys have spent a lot of $$ and time fighting it and gone as far as replacing injection pumps and doing valve jobs & head work, to no avail. There's been discussion about this before, sometimes guys get lucky and solve it playing with governor springs or swapping out injectors. I'm one of the guys who fought it with valve jobs, several sets of injectors, playing with gov springs, tweaking timing, swapping out two injection pumps, doing compression checks and blowby measurements, and in the end gave up and learned to live with it.

Your fuel pressure behaves exactly like mine and engine sounds just the same.
 
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VMacKenzie said:
1slowhatch, it is fairly common for p-pump rigs to have a slight miss on one cylinder at partial throttle between about 1200-1400 RPM. Guys have spent a lot of $$ and time fighting it and gone as far as replacing injection pumps and doing valve jobs & head work, to no avail. There's been discussion about this before, sometimes guys get lucky and solve it playing with governor springs or swapping out injectors. I'm one of the guys who fought it with valve jobs, several sets of injectors, playing with gov springs, tweaking timing, swapping out two injection pumps, doing compression checks and blowby measurements, and in the end gave up and learned to live with it.

Your fuel pressure behaves exactly like mine and engine sounds just the same.
Click to expand...

hmm.. I don't think I'll keep the truck if I cant' get it to drive smoothly.

would you think that going tighter on the gov springs might help things? I know I put injectors in it and it didn't really change anything. Same with the initial gov spring install.

I guess I could always put an auto in it with a converter...:Cheer:
 
Tighten gov springs up like said above, Your idle sounds too low, Fuel pressure looks normal for a stock lift pump. To really see if its a fuel delivery issue you need to drive the truck and look at FP under load.
 
If you want the right fuel pressure all the time and aren't strapped for cash I suggest buying an air dog, set it and forget it. Ive done the modifying the overflow valve, the tighting governor springs, and adjusting the idle. i had the same problem with mine. and the truck fell on its face at WOT. Modifying the overflow valve only helped off idle performance for a short time as it will compensate for a lift pump that is dieing, the governor adjustment was great if you like your rpms to hang and it didn't really fix anything either. The idle adjustment will help your truck run with the a/c on and when your engaging your clutch but it wont fix all your problems. What I'm trying to say is that your old lift pump is probably on its way out. Since you have lower fuel pressure then spec even at idle, at WOT or anything in between you still don't have the right amount of fuel pressure. An air dog will flow more fuel at a higher pressure then playing around with the stock lift pump will. This will fix your fuel pressure problem then you can head on to adjusting your idle to fix how it acts with a/c. I did this and i have had no problems since.
 
well I ended up running Tork Teks overflow valve. I now have good pressure at idle and 3000 rpm free rev (28+).

Truck still misses at lower rpms and runs crappy. Taking off is still jerky.

I don't think it can be a lift pump problem when it misses just reving it up with no load (and I can verify great lift pump pressure on my gauge)

What do I do next? Compression check?
 
Mine stutters at 1000 rpm and I've heard 2 things, 370 marine injectors or the 4gsk. Well that's from the intelligent ones on compd think. It doesn't bother me it just sounds funny goin thru Walmart parking lot. One thing that has impressed me a lot was adjusting the valves. My truck shook at an idle before and it runs like a new engine now. Might try it Idk I print stickers for a living so what the Hell do I know!
 
wildman6bt said:
Mine stutters at 1000 rpm and I've heard 2 things, 370 marine injectors or the 4gsk. Well that's from the intelligent ones on compd think. It doesn't bother me it just sounds funny goin thru Walmart parking lot. One thing that has impressed me a lot was adjusting the valves. My truck shook at an idle before and it runs like a new engine now. Might try it Idk I print stickers for a living so what the Hell do I know!
Click to expand...

Still haven't checked the valves either.
 
Can you post a video of what it does from beside the truck as you are reving it so we can see and hear the exhaust and get an over all view of things?
 
95-12valve said:
Can you post a video of what it does from beside the truck as you are reving it so we can see and hear the exhaust and get an over all view of things?
Click to expand...

sure, any input is greatly appreciated!

I'll try to get one uploaded tomorrow.
 
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