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Truck Hiccups...stalls...why...???

C

Chicago TDP

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Have not posted in a while but I a need some help on this one.

My truck has been hiccuping in the morning or after it sits for a while.

I will fire it up in the morning, pull out of my driveway all fine and dandy but as soon as I start to get up to about 20 mph and accelerate easily , the truck will hiccup. It feels almost like the ignition it being shut-off and then turned back on, all within 1 second.

I did notice that my pump bolts had gone loose and the TDCO was at 0.00 so I moved the pump back to my original marks and was able to get the timing back to -2.2 TDCO.

But, the surging/hiccuping is still there.

I have about 240K miles and still running 30 psi of boost....

Any thoughts?
 
It really only seems to do it cold....so I would almost rule out the PMD...also, my PMD is far far from the engine.

Lift pump... I might give that a check...
 
Chicago TDP said:
It really only seems to do it cold....so I would almost rule out the PMD...also, my PMD is far far from the engine.

Lift pump... I might give that a check...
Click to expand...

Never rule out the PMD just because its 'cold' out.... My first PMD failure happened when it was about 20* outside!
 
-2.2 TDCO that is at upper limit and probably should be coding there, I'd back it off a little maybe -1.95 and see what change that makes, you say FSD is remoted, remoted where & how, possible short in extension harness ??? poor gnds ???
 
Air bubbles in fuel? A very small air leak between the lift pump and tank would do that and not drip fuel.
 
Fuel is harder to push/pull when cold, so the dead LP could be the issue until fuel can flow easier. Or a clogged filter/sock/last ditch screen.

I have seen someone else post that thier TDCO was at -2.3 something with no timing codes, and the book for a 96 says TDCO can be from +/-2.5
 
All I've ever worked on is OBD-IIs I've heard of higher codes from others, so I thought possibly something to do with the MT2500 scanner but last summer @ Aces1's place the Car-Code scan tool we used mirrored the -2.02 seen on his truck seen on my scanner & on IIRC Matt Bachand's when we were tweaking TDCO on their trucks. & I think in my 98 manual it's saying -2.02 it's not with me to confirm but that # is so familiar to me I'm 99% sure it came from my GM manual 1st and backed up by the stanadyne spec I got when visiting Pensacola Fuel once
 
Well, it has not been hiccuping anymore...I changed nothing...but it is warmer out...

Right now, I am on the quest for efficiency and am going to leave the TDCO at the current setting. I am going to run another tank of fuel, get my MPG and then change it back to about -1.5. I believe that right now, I am getting about 17 MPG so I want to double check that and then change it so see if it changes.

After I change it, I am going to be putting a new turbo on the truck. I am going to target 25 MPG (somehow) because I believe with lower compression and the proper turbo size should yield +20 MPG.

I will post my findings as they unfold.
 
I am under the assumption that by having a low "static CR" and an increase in boost will improve you volumetric efficiency which makes your motor more efficient and is capable of handling a higher "effective CR"? Does that sound right?

Also, aren't the newer D-maxes down to 16:1 and they run higher boost to gain efficiency?
 
Chicago TDP said:
I am under the assumption that by having a low "static CR" and an increase in boost will improve you volumetric efficiency which makes your motor more efficient and is capable of handling a higher "effective CR"? Does that sound right?

Also, aren't the newer D-maxes down to 16:1 and they run higher boost to gain efficiency?
Click to expand...

the newer DMAX's are a tad over 16:1, but milage on them is also lower than previous years as well. They are getting alot of there effiency that they have via SUPER high pressure injection(upwards of 30-32K PSI IIRC) and piezo injectors that are fired at upwards of 250 V AC. Even the ones with the emissions removed still aren't doing any better than the LB7's that ran at about 18:1. Higher compression with minumum exhaust restriction tends to do the best for unloaded milage from everything I have seen. It's all about using every last possible bit of energy from every drop of fuel, and that means keeping combustion temps up to improve burn.
 
The volumetric efficiency of lower CR allows you to burn more fuel and make more power. However higher CR allows you to extract more power from less fuel.
 
Chicago TDP said:
I am under the assumption that by having a low "static CR" and an increase in boost will improve you volumetric efficiency which makes your motor more efficient and is capable of handling a higher "effective CR"? Does that sound right?

Also, aren't the newer D-maxes down to 16:1 and they run higher boost to gain efficiency?
Click to expand...

No. To get power you need compression by static or turbo force fed compression. Air expands when hot. The more force you can get from the expanding the more power you have. More power means more efficiency for a given amount of fuel. Not talking about rolling the coal for more power... More power to the crank from specific fuel consumption.

Then the EPA gets involved and while forcing minimum MPG they also want emissions to be zero. This involves messing with fuel and making it more expensive, DPF to drop your MPG via exhaust restriction, and lower NOx. Lower NOx comes from lower compression, nasty EGR, etc. The DPF etc cutting your MPG down is not the EPA or the auto makers #1 goal anymore - the emissions are! The only reason for the lower compression is lower NOx - as seen by lower MPG as a trade off.

As with everything there is a limit before you don't get anything back. The NA 6.2 2WD with it high compression was the highest MPG you could get without the fancy VGT turbo etc. The emissions from this design got the 5.7 diesel banned in CA by CARB for 1985.

Turbo's make up for the compression, but, in the 6.5 world tend to be a exhaust restriction limiting your MPG to 14-15 when it should be 18. (14-15 on a 6.5 4x4 vs. a 1988 6.2 NA 4x4 diesel burb. The 88 gasser burb was 9.) The precup IDI design was for efficiency first and power second. Turbo's were not in the original design and simply work better on non IDI engines.
 
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