Engine/Transmission (1994 - 1998) 95 12 valve sputters

[edward.tabor]

I have a 95 12 valve. It seems to run smooth at an idle, and going down the road at full throttle it runs fine. However, sitting in the shop, if i hit the throttle it pops and sputters and smokes gray. Also just cruising down the road it has a definite miss. Any ideas? I changed the fuel filters and have put a set of injectors in it but still have the same problem. Thanks.

 

[fest3er]

Hey Ed, what up? The TDI still running? Or did its bout with 10K RPM damage it?

That sounds a little like a mild version of what I went through recently: air in fuel, though it got to the point that my engine would not idle at all. At low engine speeds, it seems to draw more air than fuel. But at higher speeds, it draws more fuel than air. If you have a pusher pump back near the tank, this is less likely to be the problem, though.

 

[edward.tabor]

Lol no the TDI is still doing good these days. As for this Dodge however, wish I could say the same... ..... No pusher pump near the tank on this one. Just the factory setup. I removed the line going into the transfer pump and installed a test hose and ran engine from a bucket of fuel. It still smoked, popped and carried on. I then removed the overflow valve in the injection pump and replaced it with one from another truck. Doing this made it run a little bit better, but still not like it should. The problem seems fuel pressure related. However, i cant understand if it is not receiving adequate fuel pressure, why it would get better under a load rather than worse. At about 1000 rpms in the higher gears(this truck is a 5 speed manual), it is very choppy(almost like a miss) if you are easing along, but as soon as you give it some fuel it straightens right out. Is there any easy way to rig a fuel pressure gauge on it for test purposes? And what kind of pressure should it sustain? Or might i be looking in the wrong direction? Thanks for any help

 

[fest3er]

Hmmm. On the outlet port of the filter (at least on my '98), there is a small bolt in the banjo bolt; you should be able to install a pressure gauge there.

If the lift pump is marginal, I might expect it to operate like that. At low speed, it can't quite move enough fuel (or the check valves aren't quite sealing), but at higher RPM the pump moves more fuel than is lost. A loud-ish metallic ticking from the vicinity of the lift pump at certain engine RPMs and fuel loading may well indicate failing/sticking check valves in the LP. Marginal check valves can let too much fuel backflow at lower engine speed, but function well enough at higher engine speed.

If you replace the LP, you can almost be assured that rusted fuel lines will go next. And you can almost be assured that the quick-connect fittings, which by now are definitely not quick-disconnect fittings, will be a PITA to deal with.

In other words:

• Your LP provides fuel pressure; if it is aged and failing, FP will be low and possibly marginal; marginal or failing check valves will also affect engine operation
• You bypassed most of the supply-side of the fuel lines and the problem persisted; this almost surely points to the list pump. A sure bet would be to put an electrical pump in the bucket of fuel: something/anything that can produce 15-30 PSI. If the problem vanishes, it's the lift pump.
• If your steel fuel lines are well rusted, a replacement lift pump will most probably accelerate their failure.
• Examine your lines (steel and rubber, supply and return). If they 'look' old and are well-rusted (steel) or 'crackled' or soft (rubber), replace them, because they are probably letting air into the system. Don't be like tightwad me; do the job once.

It took me a couple weeks to get mine running well again because I 'cheaped out'. I replaced the LP and the line from the pump to the filter. It worked nice for a short while. Then it steadily and quickly got to where it wouldn't idle and wouldn't run well under 1400 RPM. And it took lots of cranking to get fuel back into the engine even 10 minutes after shutting down. I think the new LP sucked a hole in the rusted supply line; I finally rednecked the supply line and cleared up the worst of the air. It made it to MN and back last week in fine style. But it starts hard after sitting overnight, so there's air getting in still.

 

[edward.tabor]

Thanks for your help. I will be looking into it toward the end of the week, as time permits. I will let you know what I find.