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Holley TBI Replacement

dave w

dave w

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I'm helping out a friend who replaced the factory TBI on his 94 GMC with an aftermarket Holley TBI.

I used my DataMaster software to see how things worked out. Seems the Holley TBI is running rich. I've reprogrammed PROM so the fuel is 70 lbs per hour and adjusted the fuel maps.

Anyone else have a similar experience when using a Holley TBI?

dave w

Holley TBI.jpg

Holley TBI 70 lb.jpg
 
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holley tbi units need lots of help to run right.

best bet sell it and go back to a stock unit and have it bored out for bigger butterflyes. then tune from there.

thats what i have read not ever tryed. brian at tbichips has good info and links.
 
Here is the latest tune results. It's not always possible to get enough fuel information (HITS) in every MAP vs. RPM cell. When I get several hundred hits in a cell, I'm usually good on the adjustment. If I get 50 or less hits in cell, I can make a good "Course" adjustment. Sometimes it's just not possible to drive in some of the MAP vs. RPM cell. For example ... the legal speed limit of 70 MPH is 25 Kpa vs 2000 RPM. If I'm driving 70 MPH and want to quickly pass a 60 MPH semi-truck, as soon as I "put my foot into accelerator" I get to 80 MPH with 96 Kpa vs. 3200 RPM. So cruising a 70 I get lots of hits, but just a quick 80 MPH pass around a semi-truck I only get a few hits.

I guess Holley TBI's are like the older Holley carburetors, run great once the "Tuning" is finished. Well at least with the TBI, I can use a LapTop to tune and make changes to the tune while I'm driving.:D

dave w

TBI Tune.jpg
 
The PROM programming finished. Many changes to both fuel and spark tables. Custom PROM complete for the Holley TBI.

dave w

Fuel Tables.jpg

Spark Tables.jpg
 
Do you like how it runs/performs?

I had a Holley TBI unit at one time, but the ecm fried in the middle of a 13 mile somewhat difficult trail. I hate the fact that the ecm supplies power to the fuel pump instead of grounding a fuel pump relay. I also hated the fact that I could not get the ecu "off the shelf". I put a factory TBI on my engine with a cust. program prom. Love it much better.

Seeing as you already had a factory TBI, seems a waste of 1200 bucks to convert to Holley TBI system. Just my 0.02

Ohh, btw. Your tuning is impressive.
 
79chevyk10 said:
Do you like how it runs/performs?

I had a Holley TBI unit at one time, but the ecm fried in the middle of a 13 mile somewhat difficult trail. I hate the fact that the ecm supplies power to the fuel pump instead of grounding a fuel pump relay. I also hated the fact that I could not get the ecu "off the shelf". I put a factory TBI on my engine with a cust. program prom. Love it much better.

Seeing as you already had a factory TBI, seems a waste of 1200 bucks to convert to Holley TBI system. Just my 0.02

Ohh, btw. Your tuning is impressive.
Click to expand...

The Holley TBI unit I tuned was NOT a complete Holley TBI retro-fit system. The Holley TBI unit was designed by Holley to be an OEM replacement for the factory TBI unit?:confused: http://www.holley.com/types/Direct Replacement.asp In all fairness, I think the Holley TBI unit had the fuel pump pressure set wrong?:confused: Maybe the Holley TBI injectors flow more fuel than a factory injector?:confused:


I'm not sure I understand the OEM ECM grounding a fuel pump relay?:confused: Based on my experience the OEM ECM sends a low currrent 12 VDC energizing signal to a fuel pump relay coil; which then enables the fuel pump relay high current contacts to sent BATTERY "+" voltage to the fuel pump. I've worked on several industrial relay applications, where voltage is sent to energize relays, because if power is lost to an industrial relay application the equipment operated by the relay will shut down. Best I can figure things out with an automotive fuel pump relay, if the low current 12 VDC energizing power from the ECM is lost to the fuel pump relay; the fuel pump would then shut off. Best I can figure things out, having the fuel pump shut off if a vehicle was in an accident would be a GOOD THING!

dave w
 
Ohh, you just used the Holley throttle body itself. Okay.

The fuel pump relay is fed a low current 12 volt sorce by the fuse panel with it's own fuse for fuel pump. The ecm grounds the control side of the relay (low current switching side). When the ecm grounds the circuit, the relay "turns on" allowing B+ to go to the pump and turns on. Of course the fuel pump is grounded external of the relay. Ecm using grounding circuits to turn on and off components reduces the max current the ecm uses.

This has been my experience.
 
My 93 GMC wiring diagram shows the following.
Pin A Orange wire from fusible link. (Battery "+" and also goes to the Fuel Pump oil pressure switch)
Pin B Not Used
Pin C Red wire (fuel pump prime)
Pin D Black wire with White stripe (Ground for the relay coil)
Pin E Gray wire ( To Fuel Pump and and also goes to the Fuel Pump oil pressure switch)
Pin F Dark Green wire with White stripe (from ECM to Power for the relay coil)

Maybe other model years are different?:confused:

dave w
 
spastik monkey said:
if you don't have the aldl setup, what's a good way to tune these by ear?
Click to expand...

I would not try to tune a fuel injection system (factory or aftermarket) by ear.:crazy: Maybe using WB O2 and adjusting fuel pressure would work because WB O2 does not need aldl.:confused:

dave w
 
well with my tax return i'm swapping to an ls1/6l60e combo, i'm just trying to get this running decently for the time being
 
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