'81 IDI - new pump, won't rev up, lack of power in high rpm

[FieroGT42]

'81 (A1) Rabbit Diesel, 1.6 4 speed, replaced bad IP with a used "guaranteed working" unit.  It used to run great with the old pump but then got harder to start as it went out.  The new pump idles wonderfully and sounds pretty good, but sometimes hesitates and won't rev very high in neutral (guessing 2500-3000), and the car only goes about 7mph.  It takes off fairly well, but just seems to lose steam.

I've triple checked that the cam/crank/pulley timing is spot on and rotating the pump doesn't seem to have any effect on the power issue.  I don't have a dial indicator to set the timing perfectly, but it shouldn't be nearly this bad.

I don't see air in the fuel supply line, but the return lines between injectors are full of air.  I'm wondering whether it's sucking in air through the front seal (sprocket side) or just not putting out good pressure.

Any help would be appreciated as the weather isn't getting any warmer in this hemisphere.  Thanks!

[maxfax]

You mention "sometimes"..   Are there times that it will run okay???    How much do you know about the used pump??   Had it sat around for any lenght of time??   Generally when the shaft seal doesn;t seal properly you'll be able to see fuel leaking out from around it, but it is possible you're getting some air in though there...  If your pump had sat around for a while maybe thing like the vanes in the lift pump are sticking and not delivering enough fuel..   Have you tried running diesel purge or something of the sort though it???


How exactly did you old pump go out???   Leaking fuel, stop running, or just the hard starting??

[fastguy69]

A good trick that soome one on here told me was to drop your fuel filter, drain out the fuel and then fill it back up with auto tranny fluid.  My pump was doing the same thing untill I tried this and it unstuck the plunger and all the other moving parts in the pump.  It literally came to life after sitting for twelve years.  Try it out....it won't hurt anything and it will clean your injectors too.  Runs great on the stuff!

[FieroGT42]

Thanks for the help and sorry for not replying sooner - I've been pretty busy.

I don't know how long the pump sat, only that it was "guaranteed" to work or be rebuildable core.

The car would initially run well at lower RPM with the "new" pump, but would drop off in power and start stumbling in the mid and high end.  Letting it idle for a bit would let it be able to rev again.. for a bit.  Running from a jar of fuel didn't seem to make much difference, so that rules out a plugged fuel system or failed tank venting, but squeezing the inline priming bulb (which has a check valve) would make the pump spring to life, so I'm sure it's a weak low pressure end... probably stuck vanes?

I've connected everything back to the fuel tank and put a "professional" series Facet/Purolator lift pump in, figuring that low PSI would only extend the life of the pump, and it runs better than ever in the low to mid range but still seems to starve.  Running in 2nd gear, it starts to stumble about 3/4 of the way to the 2nd shift point and won't go any faster.  Shifting to 3rd, I can get 2/3 of the way up.

There isn't air in the first 3 return lines now, but the cyl 4 return line (between 3 and 4) still bubbles slowly but steadily from the #4 injector when the car refuses to rev higher.  I'm told that this could be a sticky injector or bad timing causing air to be forced through a partially open injector.  I'm pretty sure the timing isn't off by much and squeezing the priming bulb prevents the bubbles, so I think it must still be starving.

So, on to the ATF I suppose.