350tbi sluggish and fuel guzzler

**alkatyler** · 06-08-2014

I have an 85 chevy k2500 with a 350 block bored .030 over. it has flat top pistons, 5.7 rods, very mild cam, with tbi heads and basic tbi setup out of a 91 suburban. The conversion went well but I never seem to get good mileage. The truck has 4.10 gears and seems to run better at part throttle. If I mash the throttle it just bogs out a little and slowly comes to life. I installed a 180 thermostat awhile ago and it helped. I have to separate data logs that I run this morning. one with 87 octane, and the other with 91 octane. the tank was on E as usual, so the fuel test is real close.

It is backed with a 700r4, I have played with the cable and feel that it is shifting fine. just doesn't kick down as solid as I feel it should. The gear ratio with the engine I feel should be great low end. But is very sluggish and very hard on fuel. 8-10 mpg.

The knock counts seem high, and the other readings I am starting to learn. I am starting to make sense of a few things, but need a little help if anyone is interested in taking a look at the data?

**steveo** · 06-08-2014

your trims are stable but they're high which means it wants more fuel, but that doesn't explain your low fuel economy.

who tuned this?

what's your fuel pressure look like?

**alkatyler** · 06-08-2014

this is a stock 1227747, it has not been chipped or tuned.
I am wondering if there is something that is missing from the inputs?

**alkatyler** · 06-08-2014

fuel pressure is a stable 14-psi.

**steveo** · 06-09-2014

needs a tune at the least; any modifications to a speed density engine require re-tuning of the VE tables (and probably timing) -especially- if we're talking a different cam than the stock calibration was designed for.

**EagleMark** · 06-09-2014

If you download TunerPro RT and get some data logs with it I can tell a lot more.

So is the rig 4x4? Big tires? Etc... 8-10 in town is not unheard of with this type of rig. The 4:10 gears should make it drive good but if it's got 35 or bigger tires it's a wash...

**jim_in_dorris** · 06-09-2014

Mark, I loaded the log into excel and looked at it. He has a TPS problem. At idle the sensor is reading negative. He may have other problems as well, I didn't spend too much time looking at it.

**Scrufdog** · 06-09-2014

My 95 C2500 Burb, 3.73 gears, only got 10mpg when I got it. I did the Ultimate TBI mods, new balanced injectors and FPR and now I'm at 12mpg at 12.5 PSI fuel pressure (fuel pump maxed out).

**alkatyler** · 06-10-2014

the cam is an Elgine 1127 .387/.410 lift 258/269 duration 108/116 lobe center
The truck is pretty much a stock 4x4 with 285 tires. it was an 85 chevy, now with a EFI top end and 700r4. The VSS is in the transfer case, and I had to make the module adjustable for the proper speed to match the tires.

The negative on the TPS is bothering me as well. When I mash the throttle to WO it goes, but doesn't kick down and GO!! Just feels like there is something easy missing.

I tried to use Tuner Pro, but am stuck trying to get the files and downloading figured out.

Thanks,

**Scrufdog** · 06-10-2014

If your cammed up with bigger tires, then 8-10 mpg isnt bad. However, I can confirm as mentioned previously, that the TPS looked whacked out. That would explain lack of power and improper shifting. You should test your TPS with a multimeter and likely replace it. If you replace it, get a Delco one, as a lot of aftermarket ones are hit or miss.

**EagleMark** · 06-10-2014

Check the TPS with DVM and should be a nice smooth transition from 0 to 5 volts or close to both ends. When at idle it should read close to .54v Have you messed with the throttle plate adjustment? If so it may explain what's going on, it won't set idle! It's a minimum Air Setting.

Download the TunerPro RT from their website and then read this:
http://www.gearhead-efi.com/Fuel-Inj...is-a-must-read!
It should make things clear as to what each file does.

Here's some instructions to installing the cable to TunerPro RT:
http://www.gearhead-efi.com/Fuel-Inj...to-TunerPro-RT

I'm guessing the ECM is 1227747? What chip BCC is in it?

If it is 1227747 that is mask ID $42 and you can get the XDF file for making adjustments to the chips .bin file and the .ADX for Aquiring data from here:
http://www.gearhead-efi.com/Fuel-Inj...Information-42

It's way worth the effort to get TunerPro RT working and getting used to the software, it's not that hard but the returns on what it can do are enormous compared to WinALDL.

Have you set timing to 0* with bypass wire disconnected? It's sometimes hard to get the engine to idle while disconnected but you can use a feeler gauge in throttle stop to raise idle, do this with engine warm and keep it under 1000 RPM. Could even set timing to 5* will help the cam a little, but no more or you could be creating knock etc... elsewhere.

Your knock counts were going up but not a lot. Double check it is correct knock sensor and wiring is all in order. If you replace knock sensor tourqe it, it's low. Or you will squeeze it to tight and it becomes to sensitive. Retarding timing does not help performance or MPG...

**alkatyler** · 06-12-2014

ok, I got it downloaded and made a test run. a long run with a lot of various driving conditions. I did notice that I had the A/C on and the clutch was kicked in but it showed no a/c. The kickdown light would go green if I was simply cruising with no hard acceleration. I am sure you will see more than I do. But I will play it through again and watch myself. The timing is set at a base of 0. The truck idles great and runs fine, just very sluggish when you ask for power. The A/c kicks in and out during idle and the engine comes to life as it does. I mean it doesn't stumble and die.

**jim_in_dorris** · 06-12-2014

I looked at an old log of mine, and yours doesn't look too bad. I did notice a couple of things, 1 of which might affect your power. It looks like your IAC counts are a little high, especially at idle. and secondly, your high gear switch never shows HIGH, just LOW and mine switches.

**alkatyler** · 06-12-2014

I was noticing the loop temp? was up and down a lot. While the engine temp is stable. The O2 sensor is the same way. The kickdown light is strange and with the high gear switch as well. I am wondering if it is a bad ground or if I do have a wire screwed up. I am starting to just watch the playback more. I did set the cruise at one point, actually just before the kickdown light comes on. The cruise is intermittent and shuts off on its own. I don't know remember how it is wired in.

When I did the transplant, I remember laying out both harness's out and comparing them. The one from the 85 original truck, and the one from the donor. it all matched up well if I remember except all the new sensors of course. I used the electronic dash out of the burb so I would have the engine light and all just as stock. I am pretty sure the burb had the 700r4. I did not at the time, so I put that in mine also with the transfer that had the vss sensor to run the system. wondering if I need to do a pin-pin inspection of the wires?

In the playback there was a couple of WOT runs for a short time. When I did, there is no noticeable kickdown and go. more like driving an old turbogluide just uses the engine to push through the power band.

**alkatyler** · 06-12-2014

I was just noticing that when the key is off, it shows as high gear on, and that the shifter is in park.
When I turn the key on, shifter goes to drive and high gear goes to low???? didn't move the shifter, is this a switch I need to worry about?