Fuel Pump Trims

[iamdub]

Slow crank as in the speed the starter is turning?
Or slow crank as in the starter is turning at normal speed but the engine takes a while to fire up?

Has to be the latter. The PCM doesn't alter the starter cranking speed at all, regardless of any sensor input.

BTW, did anyone else notice Scotty put the rubber ring on the inlet side of the MAF clocked incorrectly?

 

[BG1988]

Slow crank as in the speed the starter is turning?
Or slow crank as in the starter is turning at normal speed but the engine takes a while to fire up?

Starter turning at normal speed but the engine takes a while to fire up....intermittent from autostop


I did get a Code for the 12V+system (Voltage dipped below 9 volts lost power..)
12v+Battery deemed faluty on Sept 10th( was flat overnight from cold spell )

I replaced my 12Volt battery on the oct 25th

with a HIGHER CCA, 760CCA

this one
https://www.walmart.com/ip/EverStart-Platinum-AGM-Battery-Group-H6/40647528

I got the AGM Deep Cycle battery as i know the Tahoes deeply discharge the batteries while running. "to save on gas"


Looks like the quality improved as they give a 5 year replacement now (as seen on the battery label ) instead of the 3/5year prorated..

fresh stock


if you have a intermittent starting issue it's the battery(cant supply enough Current to everything and voltage is dipping below 9 volts upon cranking) or MAF sensor if it cranks and takes a few tries(or the flywheel is damaged ) if it's warmer i.e 85F you can get a bit more current out of the battery compared to say 50F or 30F etc

 

[swathdiver]

Fuel Pump Trim at 1.49. Truck at 155K miles now.

 

[swathdiver]

Ok fellas, it's been three years so let's try this again. Those with advanced scan tools, can you look in your Fuel Pump Control Module and post up your Fuel Pump's Long Term Trim number?

Last time I checked mine a few weeks ago, it was 1.54 at 190K miles. I'm going to take both trucks out in the next few hours and note their LT Trim number and see how much the fuel pressure fluctuates at idle, normal driving and WOT and will report back.

 

[swathdiver]

Last evening I ventured into the shop manual and while I saw LT and ST Fuel Pump Trims mentioned, there was nothing else said about them and how it works.

Remote started the Yukon and a few minutes later after getting the Tech-2 fired up the LT Fuel Pump Trim read 1.70. During the 2 hours I was on the road picking up parts and having lunch, the trim reached a high of 1.74 and a low of 1.68. I was doing a Live Plot of the fuel pump pressure this whole time and it never dropped below 42 psi or exceeded 45 psi. Most of the time it was spot on. Idling and cruising around the fuel pump duty cycle remained in the 44% range plus or minus 3% except for full throttle runs either from a roll or such as when passing out on the highway, it went about 10% higher very briefly.

Oh, when I set up the Live Plot for the LT Fuel Pump Trim, the scale was set from 0.0 to 4.0. So, if this a sign of pump heath, I'm still under the halfway point to my way of thinking? What say you? Anyone but me ever look at this stuff? LOL

 

[mikez71]

Ok fellas, it's been three years so let's try this again. Those with advanced scan tools, can you look in your Fuel Pump Control Module and post up your Fuel Pump's Long Term Trim number?

Last time I checked mine a few weeks ago, it was 1.54 at 190K miles. I'm going to take both trucks out in the next few hours and note their LT Trim number and see how much the fuel pressure fluctuates at idle, normal driving and WOT and will report back.

My long term stored value is 1.29 (208k miles).
How did yours go from 1.49 couple weeks ago to 1.70?

 

[swathdiver]

My long term stored value is 1.29 (208k miles).
How did yours go from 1.49 couple weeks ago to 1.70?

I guess it's getting old? Wish I knew what the number meant and not just my guessing.