1991 TBI Tuner Pro RT Data Analysis

[WICruiser]

I have a 1991 Silverado with the 5.7 TBI engine. I have Tuner Pro RT and have logged a few (one for sure, not sure what happened to the other) data streams while driving. Generally things seem about as expected except that whenever my throttle opening gets up near 50% my vacuum goes to zero. Maybe that's normal but it seems to drastic. Idle vacuum is good, transmission shift points seem about right. Overall the truck seems like it is dragging an anchor and fuel economy stinks (10 mpg empty, 8 towing a trailer). Transmission will unlock with just about any throttle or load input, and it will downshift out of OD to maintain 70 mph empty (worse with the trailer).

Any thoughts appreciated.

[WICruiser]

I rearranged the dash on my Tuner RT Pro and one of the gauges I added was spark advance. When I play back my data file it looks like I am not getting any spark advance at any time. That may explain a lot about the performance (or lack there of). I plan to look at the distributor but any recommendations on what to look for would be appreciated.

[jim_in_dorris]

the spark advance gauge will only work if you have enabled in on the chip, it is a patch. Things to look for would be fuel pressure, spray pattern of your injectors (if only 1 is working it will run very poorly off idle). what do you spark plugs look like? is it running rich? or lean?

[erjbsa]

Check your MAP sensor for a dead spot. Use a vacuum hand pump and watch the readings on Tuner Pro.
0 in. Hg ...... 4.7 Volts.
5 in. Hg ...... 3.9 Volts.
10 in. Hg .... 3.0 Volts.
20 in. Hg .... 1.1 Volts.

[WICruiser]

erjbsa - thanks I will check that out.

Jim - Can I enable the chip in my std. production ECU with a patch to provide the advance gauge function? If so where is the patch available, and how do I write it into the ECM without changing anything else?

FYI, I did confirm that the timing is moving with rpm using a timing light. I think my base timing was a little retarded so I reset to "0" with the timing set wire disconnected. However, it would be nice to know that the timing is doing as I am running down the road.

[jim_in_dorris]

Unless I am wrong, you have a 7747 ecm which is a $42 mask. The patch was put into the tunerpro rt definition file by eagleMark. Look for the patch at the top of the file in tunerpro. You will have to burn a chip to get it to work.

[WICruiser]

I agree that I should have the 7747 ECM (not sure what I actually have given the lack of vehicle history) but I am using the $85 mask. I believe the $42 is for the 5.0 L and I have the 5.7 L. I am not planning to burn a chip so I will forego capturing timing advance, at least for now.

Thanks

[jim_in_dorris]

no, $42 also has 350 bins, I run it in my truck. If you are truly running $85, then you have a 7060 ecm which is for 4l80E transmissions. If you have a 7747 and are using the $85 adx and xdf, you data will be wrong. totally different masks. the ECM is behind the glovebox I think. you should be able to see the sticker without removing it. Since you are not tuning, just trying to see what is happening, I wouldn't remove it right now.

[WICruiser]

I finally got a chance to check my MAP sensor.

I forgot to capture the 0" vacuum reading but it seems pretty good everywhere I checked:
5" Hg - 3.82 volts
8" Hg - 3.27 volts
10" Hg - 2.92 volts
12" Hg - 2.55 volts
15" Hg - 2.00 volts
17" Hg - 1.67 volts
20" Hg - 1.12 volts

With the base timing reset the fuel economy seems better (roughly 11 or 12 MPG when towing vs. 8 prior).

I need to capture some data with the timing change to see what the knock sensor is doing but I do not hear any ping noise.

[WICruiser]

I finally got a chance to check and indeed I do have the 7747 ECM.

I am getting better at using the software to record data, now all I need to do is decide if it is telling me anything.

The base timing advance really did change the performance and I believe the fuel economy. I should really determine how to confirm where the timing is (the timing tab is rusty and hard to see so no real numbers are visible.

One thing that I thought was odd is the knock sensor is still only reading 1 or 2 events. I am not hearing any pinging but I expected more knock sensor activity with the timing change. It could be I am not really getting a knock sensor signal so I am not banking on the number meaning anything.