Odd, just odd

[kconnair]

Well,

Our '86 suburban suddenly started running very poorly, very very poorly - got worse when hot. Wouldn't go over 45 - surging with medium - wide throttle in neutral, surging at med to high revs in gear, blowing whitish smoke - not black. Keep in mimd that the mechanicals are ok, head gasket seal ok - not loosing antifreeze out the tailpipe or into the crankcase. Thought well, it's misbehaving hot, but not so bad cold, must be the IP - getting hot, those loose clearances are making it lose that precious pressure necessary to pop the injectors.

Wrong.

Swapped out the IP, truck ran the same.

Replaced the Fuel filter - Wrong answer - ran the same.

Replaced the lift pump - Wrong answer - ran the same.

So back to the basics of trouble shooting a diesel injection system.

pressurized the fuel tank - no leaks evident anywhere. Filter mount clean/clear. Rusty rear lines - no leaks.

Drove it - still the same behavior. ????

Replaced the lift pump to fuel filter rubber hose with clear plastic to check for bubbles. Primed the fuel filter assembly until all the air was purged.

Started it, now it seemed better, drove it to get it warm to duplicate the problem. Seemed to run ok. What now, the truck will even make it up to 80 and still accelerate!! Drove it up a hill it could barely climb earlier. Went up fine - even accelerated up the hill! WTF! :confused: :eek:

I hate problems that seem to fix themselves. :mad:

It must have been that high performance clear fuel line :eek:

Any Ideas? Anyone? :confused:

Thanks,

Kevin.

[Peter J. Bierman]

Sounds like fuel starvation to me.
If you feed the engine not enough fuel you lose performance, if way to less fuel you even affect timing couse it partialy controled by fuel pressure.

Just a thought ;)

Peter

[kconnair]

Thanks Peter, I wondered about either an air leak, or a blockage, but thought it very odd at how quickly the symptoms happened. Driving fine - then after a short stop driving poorly. At first I was sure the IP had just had enough. Now I am just scratching my head.

Thanks again,

Kevin.

[NH2112]

I had something similar happen over the past several days. Earlier in the week I pumped some fuel from a friend's backhoe into my tank so I'd have enough fuel to make it to the gas station. Here's what happened:

Tuesday night: Truck surged several times while at steady throttle setting, after driving maybe 12 miles. No other problems.

Wednesday morning: About 10 miles from home the truck started surging, bucking, losing power, blowing puffs of grey smoke, etc. I replaced the primary filter when I got to work, it had about 25K miles on it.

Wednesday afternoon: Truck ran crappy on the way home, I think it died right as I pulled in the driveway but with a bit of cranking it started up again.

Thursday morning: Ran absolutely TERRIBLE on the way in, losing power, bucking, surging, HUGE changes in timing, etc. Got it to work eventually, changed the primary again and put a new secondary on it (that had 25K as well.) Drained the tank, put clean fuel in.

Thursday night: Had a few surges, and maybe a buck or 2 on the way home.

Friday morning: Barely made it in to work, it ran the same as it had the other 2 mornings - stalled 1/2 dozen times or so, etc.

Friday afternoon: Died after maybe 15 miles and I didn't even bother trying to get it running again.

Sat morning: Got someone to come out with me, started it up, within a few miles it was acting up. Died 6 or 8 times on the way to the shop, got it running again every time but rarely went more than a mile. Towed it the last mile or so. Opened the fuel filter drain while cranking and hardly anything came out after 30 seconds of cranking. Put new lift pump in today, *may* have had a surge on the way home tonight but more likely I'm so paranoid that I'm feeling things that aren't there LOL

I'll see how it acts over the next few days, I have a good used pump so I can swap them out if necessary. Maybe I'll keep a jug of cold water in the truck to see if it helps if the thing dies again.

[opto]

Phil, what was your conclusion???

[NH2112]

I ran temporary fuel lines to a 5-gallon bucket in the bed and had absolutely no problems so I dropped the tank, cleaned it out, and put fresh fuel in. It ran great after that, but in the past month or so has begun acting up again with classical symptoms of fuel starvation (bucking at high RPM/highway speeds, surging, timing changes, etc.) I've drained the tank, replaced fuel filters, etc, and haven't really seen any change so I'm thinking it's the IP (original at 280K or so miles) due to the fact that it's worse when the temp is warmer. On cool days it only does it after maybe 10-15 miles at 70mph, on warmer days it'll do it after only a few miles at 60mph. I'll put my good used pump in when I get a chance and hopefully that takes care of it.