jkarner

My stock 96 12v with 250k has been running rough/hestitating under acceleration especially when engine is cold and seems to be getting worse in the 35k I have driven it, so I know it's changed and not just the cold-blooded nature of the 12v. Blows whiteish smoke if I accelerate too hard during warm up but it improves quite a bit but doesnt go away completely once warmed up. Once the truck is higher in the rev range, above 1800rpm it seems to run better and not miss or shudder. Air filter is "newer" BHAF huge air filter and I dont drive dusty roads.

Fuel pressure is 22 at idle and 18 going up a hill and 28 going down a hill. Never drops lower than 18 even when missing/shudddering. Cleaned fuel prefilter screen, new fuel filter, and new adjustable stock settings Torqtek OFV. My truck is bone stock and haven't adjusted the valves in 35k and have never touched the timing since I bought it with 215k on it. No visible fuel leakage anywhere from hoses. Is there a pickup strainer in the tank that can clog or do i have an invisible air leak somewhere?

Not totally sure where to go from here, some guidance would be much appreciated!

patdaly

FP is just a tick low, don't believe it is the sock, your fuel pressure would drop much more if it were a restriction.

Take a pair of visegrips and pinch off the return hose before it turns back to braided at the engine and see if your FP jumps up to 60 or so.

gorms

Could be sucking air between fuel heater and pickup tube. Pressurising the tank with a few psi and checking over everything closely may help find it. My pickup screen was clogged almost completely solid with black goop at 230k, sure wouldn't hurt to check it.

jkarner

Thanks for the replys. Patdaly, where exactly is the access for that return fuel hose? All my fuel lines visible from above the engine seem to be steel. What might be happening if my pressure doesn't hit 60psi? Also, my gauge tops out at 60 so hopefully I dont break it if I try that.

I did thoroughly clean fuel preheater screen. There was some debris but cleaning did not fix the issue. So Gorms, did you mean that it might be leaking air somewhere between the pickup tube in the tank and the lift pump/preheater? What's the best way to lightly pressurize the fuel tank?

patdaly

Here is a picture, the return line is rubber from about the back of the engine to the metal return tube from the Injection Pump. This picture has that line colored red.

Dodge Ram Picture by infidel | 3523122 | Diesel Truck Resource

If it doesn't jump significantly when you pinch off the return line, it means your Lift Pump is not putting out enough pressure. Essentially, these things have an oversized Lift Pump, and the overflow valve on the back side of the IP regulates the pressure the pump sees, so we have a significant amount of fuel being returned to the tank under normal operation, you further restrict that flow, and pressure naturally will rise, if it is available. I doubt your gauge will be harmed, but you don't have to pinch it totally off, have someone watch the gauge while you start to restrict the hose.

And yea, these things are getting old, and air leaks form pinholes in lines or cracked rubber will cause you issues.

gorms

I have a rubber stopper that fits in the filler neck, with a hole in it for a blow gun to put a little pressure in via shop air (any air compressor will work) for filling new fuel filters, will show leaks in both lines as well. Fill it up with a few psi and look carefully over all lines/fittings for any leaks.

Have you ever checked timing? Not sure how it would run at higher rpms with slipped timing but may be something to look if all else fails.

jkarner

Never checked timing on this truck. Is it tough to find out where it is and if it slipped? I will try to pressurize the tank with a rubber stopper and see if that produces an obvious fuel leak and also the pinching of the return line to see if pressure rises. From Joe G's fuel system writeup, seems like even though the system is simple there are still a number of places that have caused people problems with air making its way into the system.

Seems like I would see a significant pressure drop below 18psi though if I was drawing air, so I guess that's what had me thinking about timing. Anyone have thoughts on that? Maybe the fuel pressure is not the ultimate telltale of a minor fuel system air leak?

jkarner

Anybody got any other suggestions within the scope of the fuel system not related to air leaks because it seems like an air leak is going to really show up as a pressure drop at the IP? Im still plagued by this problem and I'm not dropping below 18 psi at the IP and the truck does not have a problem starting but likes to be plugged in during the winter here in michigan. How do I go about checking things like injectors/IP? The truck really bucks and blows blueish smoke under heavy load if I get on the throttle too quick and doesnt stop doing that unless I back off and more slowly get the truck up to speed. Only seems to happen before the boost kicks in because it takes off once in the boost after 1700 rpms or so. Thanks for the input guys

gorms

You can still make fuel pressure with some air bubbles getting in.

Just re-read the thread, have you checked that the shut down solenoid is pulling all the way up, and that the arm connected to the shaft on the pump is tight?

Still sounds like air in to me, got to start somewhere....checking timing is another easy thing to rule out. There are better explanations than mine on how to pin time it, but basically there is a plug on the rear of the front timing cover, under the p7100 towards the block. That plug when turned around fits into a notch in the cam gear at TDC. At the same time, on the injector pump, side of pump under AFC area, is a 15/16" hex head plug (off memory) with its timing pin underneath it. Just a plastic plug that will accept what looks like a flat screwdriver tip. That plug will fit in the opening and accept the little timing arm to represent TDC.

If these two pins line up then it is in time.