PFF - Pennock's Fiero Forum, PDA Edition

What MPG With a 7730 Conversion? (Page 1/2)

fierofool

MAR 28, 04:28 PM

I have an 87GT with 5 speed, stock 3.4 with a 7730 conversion. The injectors are rated at 14# instead of the 17# I was told when I bought them. Real time scanning shows I'm running lean. Before the 7730 conversion, I was running rich and still getting 16-20 MPG and sometimes even as much as 24 MPG.

The quandary: I am only realizing 12-16 MPG at highway driving conditions. I'm curious as to what others are getting, and what injectors are being used.

Gall757

MAR 29, 09:49 AM

I would get 17# injectors before I would worry about the computer. It may be going crazy trying to adjust to the lean condition.

olejoedad

MAR 29, 09:56 AM

Good advice.

Dennis LaGrua

MAR 29, 10:54 AM

Yes I believe that 17 lb injectors were std on the 3.4L P/R engine but IMO getting it all to work with the 7730 may require detailed scanning and reprogramming of your ECM. You may wish to consider a wideband O2 sensor gauge that will provide fuel mixture readings at all RPM and load points. There are PC programs that can provide detailed scan data but I use an old Auto X ray unit for OBDI.
A fast way to do this would be to locate a person that has already optimized the program for the 3.4L, and have it burned into the chip. IMO, your highway gas mileage figures are way off the mark. I would expect somewhere in the neighborhood of around 27 hwy MPG with your engine but others using your combo can advise on that best.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

fierofool

MAR 29, 12:04 PM

I had a set of 17# injectors that I was running with the stock setup, but they were too rich, so I sold them. Now, I can't find them at a reasonable price. InjectorPlanet was where I bought them before, and they're just over $100 for a reman set of 6. But, they're sold out. Other sources are at least $40 per injector. 16.76#/hr @43.5 psi.

Gall757

MAR 29, 01:19 PM

Pull 6 out of a 3.4 junker and send them to a cleaning service. I am guessing there are still a lot of 3.4s in the yards, and therefore cost effective.

fierofool

MAR 29, 03:54 PM

I had used original multec injectors in a 3.4 install in my brother's 86GT, but he was running a stock ECM and distributor. It was so rich you couldn't drive behind him. The 7730 might be better able to control the multec injectors, so that's an option. Thanks.

fierofool

MAR 29, 04:47 PM

I just found the 0280150415 Bosch injectors I had used before. Will be trying them on the 7730 setup. CS Performance Fuel Injection. https://www.cspinjectors.com/
Full set of 6 at $129.00 with free shipping.

Dennis LaGrua

MAR 29, 09:44 PM

The ECM uses a parameter called the BPC or base pulse constant on which the fueling for a specific injector flow is based. I have the formula to obtain the right BPC for your computer and I'll try to find it and post it later. You will then need to find someone with an OBD 1 program editor and a prom programmer to change the program. some good info on the tools here:
Moates GM ECM Tools

fierofool

MAR 29, 09:55 PM

When I had Sinister build the chip, the 280150415 injectors were in my spec sheet. I had the chip burned more than a year ago and had since replaced the 415 injectors because they were too rich. I only got my conversion done last month. When I get the 415 injectors installed, we'll see how they perform and go from there. I do have someone local that can reprogram if necessary or I might need to send it back to Ryan for adjustment.