Hicups- need help

[DKeen]

Here is the issue. 1996 w/ 70,000 miles. When under heavy throttle, I get a miss/hicup. Here is what I have done.

New lift pump
New electronic filter
New OPS
New filters
Turbo Master
New tank and sending unit
New PMD w/cooler
and finally new IP set at -1.94

this is driving me crazy and broke. Am I missing something here?

[Andy Chesek]

Do you have a boost gauge?


If not, chances are your Turbo Master is allowing too much boost and the computer isn't happy... therefore it will cut the fuel. Had this happen to me with my '99. If you don't have a boost gauge, loosen the spring a little and then take the truck for a spin. You may have to adjust it a few times to find the sweet spot where you'll get all the boost you can from the Turbo Master yet keep the computer happy. The instructions included with the Turbo Master tell you roughly how compressed the spring should be, but in my case it was off a good bit (had to uncompress).

[Cowracer]

deteriorated fuel lines letting air into the system maybe? Especially from the tank to the lift pump.

Just a guess

Tim

[99gmccrew]

Have you checked out your ignition switch? I have read here someone fixed thier similar problem by replacing the switch and ignition harness.

[moondoggie]

Good Day!

This sounds like classic lack of fuel to the IP

[Andy Chesek]

moondoogie,

My truck ran with the hiccup for at least a month before the SES light came on. I'm sure everyone's experience will be different, depending on how hard they drive their truck. Under light driving, I never had the hiccup. It was only when I flogged the truck for a while that I'd get it to hiccup.

[moondoggie]

Good Day!

Cool! That's why I hope DKeen checks actual fuel at the IP inlet, & hooks up at least a temporary boost gauge (my temporary one has been laying on my dash a couple years now). Budgets being what they are, I try to not change parts without some hard evidence of a fault.

When I overboosted, the needle on my temporary boost gauge looked like it was going to make a couple revolutions, so boost was headed WAY over. From what you've said, it looks like there may be a boost level that's enough for the PCM to cut fuel without lighting the SES light & setting a code. Poor software, methinks, but certainly possible, based on what I've seen in the rest of the design of these trucks. (Don't get me wrong, I love my trucks, but they're a ways from perfect.)

My daughter's 89 pickup had an OPS that was partially open - it was providing a little power to the lift pump, but not enough. Man, was that weird!

Blessings!

Brian Johnson, # 5044

[gwaidman]

Just a thought here, but I have had 3 'hicups' in the last 6 months or so. Everything checks out ok, but could a worn out timing chain do this? This is one of the last things that I have to replace, but am sure that there is lots of miles on it. Thoughts anyone??

[GMC Hauler]

I recently experienced hiccups after a lift pump replacement. I didnt bleed my fuel filter assembly, after having a almost bad experience with fuel spilling all over a running engine.

I bled the fuel filter of all the air and never had any more problems.

[gwaidman]

Well, it all seems to make sense now. I stopped for a coffe today, and noticed a fair sized puddle under the truck. Now, I was always wary of a leaking rear main, but not to this extent. Further investigation of the asphalt told me that I was leaking diesel. Back home I went over the fuel system and found that the fuel filter assembly was leaking at the heater wires. From the look of the lifter valley, its been going for quite some time now. I will be replacing the rubber fuel lines as well, since I am already this far. Not a hard job for anyone, and I can bet that this is the cause of my hicups. Maybe my main seal is okay after all! :rolleyes:

[DKeen]

I will bleed the fuel lines again to see what happens.

I did get an Over boost code before the IP replacement. I will go over all the lines and filter assembly also.

I will keep everyone posted on the outcome.

[gwaidman]

-UPDATE-
Well, filter assembly installed and hoses replaced now. No leaks! I am amazed how much fuel can leak through the heater wires. New fuel heater is made from plastic. Drove the truck 120km today and it ran like a champ. :cool: