7.3 idi runs like an animal on cold advance

[Chumwon91]

I was in a hurry this morning and didn't have time to let it fully warm up to get off the cold advance like I usually do but WOW! It honestly ran so strong it was almost violent!

This is my second 7.3 idi turbo with my first being 92 auto and this one a 90 manual both duallys. This one has never had near the power the first did. And I figured the manual would have more pep compared to the auto. It has rebuilt injectors. I've re timed the ole girl several times. It has the ats 088 kit and the pump is tagged rebuilt from the shop that did the turbo kit yearsss ago.

So my question is what does the cold advance do to the ip? I've ran it retarded and advanced but never felt power like that. I'm guessing my old pump is wearing out and something happens during cold advance for it to perk up for a minute? It literally laid me back in my seat and sent my poor basset hound to the back seat! It almost wanted to surge aswell but just slightly.

Any ideas or input would be greatly appreciated! Thanks everyone!!

 

[Nero]

Ive had mine do something similar, but with a freshly rebuilt pump, its weird. Doesnt do it every time and seems to do it less and less. But when the cold advance is energized, so colder than 140f, engine torque was normal from idle to 2000, but there was a noticeable jump of power where it just wanted to take off and go hard. When the cold advance turned off, that went away. I just keep running fuel cleaner through it and keeps getting better.

 

[Chumwon91]

Yeah that is pretty much exactly what mine did. Woke right up in the mid rpm range and yep could instantly tell when the cold advance went off as she was back to her normal mediocre self.

 

[Nero]

Sadly I havent figured out what is causing it, ive asked a few pump builders and they are also stumped. Glad I'm not the only one now. But like I said, the more fuel cleaner I use the less touchy its becoming.

 

[Chumwon91]

Hmm what's actually funny is I've just started running more fuel cleaner through it aswell.

I just wish I could get that power all the time!!

 

[IDIBRONCO]

And I figured the manual would have more pep compared to the auto.

Sometimes. The automatics will actually do better a lot of the time since your engine is kept in or closer to the power band more often. From my driving experience, the GM 6.5s run WAY better with an auto trans. Their manual 5 speeds have gear spaces that are extremely far apart. They will drop 1500 RPM between gears. Unless you're at pretty high RPM (I would shift at 3000RPM), this will drop the engine clear down below the boost range with every up shift.

 

[KansasIDI]

Their manual 5 speeds have gear spaces that are extremely far apart

Yeah especially between 3rd and 4th. Because… NV4500

 

[BeastMaster]

Maybe it has to do with your TPS ( FIPL ) settings? Mine are really touchy.

And I noticed my settings would change when the cold advance solenoid changed state upon warmup.
-----------------------------------------------
You guys might find a box of these handy. I found them quite handy to monitor TPS voltage and tach sensor during operation.

https://www.amazon.com/120-PCS-Wirefy-Electrical-Connectors/dp/B077YB123S/ref=mp_s_a_1_11

[Edit] Nix my above advice on those wire taps. Within seconds of my post, warnings were posted on how they would cause all sorts of corrosion issues.

I thought I had discovered a handy test aid...looks like others before me learned the hard way..looks like I will be coating mine in dielectric grease! )

[/Edit]

-------------------------------------------------

My TPS cold is presently set to 1.33 volts ( cold, idle, engine not started ) to 4.32 volts ( still cold, engine not started, WOT ).

Use a long T-27 Torx Star driver to loosen the TPS sensor mount bracket for adjustment.

Has anyone had those adjustment screws completely out or know their thread and length? I was afraid I might lose one and never find it again...and I think it would behoove me to have some spares knowing how fumblefingered I am.

I had a erratic tach sensor that had been driving me nuts for the past year. Every time I would mess under the hood, it would sit tight and fly right, then when it sensed I was 20 miles away, it would act up.

 

[Nero]

Those are essentially scotch lock wire taps. They are the worst thing ever in existence, it cuts the insulation and then the wires start to corrode from the inside. Find them all the time in RVs and they cause nothing but issues.

 

[IDIBRONCO]

Those are essentially scotch lock wire taps. They are the worst thing ever in existence, it cuts the insulation and then the wires start to corrode from the inside. Find them all the time in RVs and they cause nothing but issues.

Those, along with 16.5" rims and tires, should be illegal!

 

[Nero]

Funny you mentioned 16.5 rims, I just sold all my srw wheels to a guy converting his '78 f250 to 16" cause 16.5" are so dang expensive

 

[BeastMaster]

Those are essentially scotch lock wire taps. They are the worst thing ever in existence, it cuts the insulation and then the wires start to corrode from the inside. Find them all the time in RVs and they cause nothing but issues.

Thanks! I had just run across these while researching ways to tap my signal lines so I could catch my gremlin in the act. I wasn't aware of the corrosion experiences. What you observed makes perfect sense. I've used "stake down" connectors and "IDC" connectors a lot ( but in a different environment: network cabling ) and extrapolated they would be good for this too.

Thanks for the heads-up.

 

[Chumwon91]

Yeah I tried it again today and it's normal power til 2300ish then wakes up all the way through the upper rpms. It doesn't smoke at all while doing it and egts stayed low.

So how does the advance on the injection pump work? Just mechanically adjusts the timing through an electrical signal?

Would it be terrible to wire it fully on or even maybe on a switch for the heavier pulls and bigger hills? I'm sure it's probably frowned upon but I'm curious on how it works and what it's *******.

Thanks everyone!

 

[Nero]

My brief understanding, and I'm no db2 expert, is that it works off case pressure. Bigger pumps have lower case pressure, some even knock out the glass check valve in the pump return, essentially lowering case pressure to zero for the very large pumps (200cc up)

Maybe the check valve is getting stuck open?

 

[hacked89]

this is a good explanation - credit to Justin
“
So a quick blast on pump operation from inlet to outlet...

Fuel goes in the cone, enters the vane style transfer pump which bumps total hydraulic pressure based on speed (and bleed, but that's tunable). From the transfer pump, it goes 3 directions: 1) pumping plungers, 2) timing advance mechanism (high pressure), 3) residual to the housing (which contributes to housing pressure, this is important).

Obviously the volume into the plungers goes out to the injectors. The high (transfer) pressure end of the advance ends up as housing volume as well after it completes it's function. Both 2 and 3 end up as housing pressure. Housing pressure is the other side of transfer pressure at the advance piston. The little timing actuator on the side of the pump determines how much pressure differential goes on in that mechanism... Beyond that, too much housing pressure will keep the plungers from filling.

The regulator fitting on top of the pump has a little check valve in it. In natural form, it regulates housing pressure to 10-12psi... The solenoid for the cold advance opens the check valve, and drops all housing pressure. Dropping all housing pressure makes transfer pressure advance the timing”

I knocked and drill out the Regulator fitting on my HPNA modded derby pump