Im having a problem with my gas mileage on my TPI 305 equipped 87' Monte. I get about 17 MPG mixed driving, which is more than half city. When the car was still bone stock, it got 18-19 MPG mixed(with the carb. and factory restrictive exhaust/flat tappet cam), the same amount city/hwy percentage...so it has me puzzled.

Info on the car:

3.08 gears, 2004r trans rebuilt, original 87' LG4 motor with a 87' TPI setup on it using the stock wiring/ECM and chip. Converted to a roller cam using the cam from a 5 speed 88' 305 TPI Trans Am. New Bosch Ford application 19# injectors, Hooker headers/catback exhaust, all emmissions/sensors are hooked up and believed to be working. ECM thinks its still in the 87' T/A it came from the way its setup.

Timing is about 10 degrees advanced, K&N open air cleaner, Delco TPI application fuel pump.

I had a few codes, 32, 33, 42 and 43 but cleared them and in the past week only code 32(EGR) came on once right after startup and stayed on until the car was turned off. The code 33(MAF) I believe was due to the relay not being plugged in all the way( ) since the tab broke off during the conversion. 43 was probably due to the timing adjustment that took place. So the EGR is the only code I currently have.

Fuel pressure was 42psi I believe when checked after setting the TPI up, and doing the IAC/TPS sensors.

Im not sure what the expected mileage is but in talking to the Monte guys who have done TPI swaps, it should be much better. Another guy with a 86' LS put TPI on his 305 and with the 2004r and 3.08's hes getting 24-25 MPG. I was expecting 21-23 mixed MPG. On a long trip all expressway a couple weekends ago I got a best of 20 MPG...with the carb the same circumstances I got 23 MPG . I try to keep my foot out of it, and do so that shouldnt be a major problem.

Any tips/ideas on what could be the *problem*? It runs/feels good and healthy, temp is at 170-175 and gets good oil pressure, etc.

All I can think to do is a basic tune up with new plugs/wires/cap/rotor even though the plugs are pretty new, gapped at .35 and checking into and fixing the EGR code for good.

Thanks!

 

I'm sure the egr is hurting you. The only other thing I see is that the ford injectors are rated at 37 psi and you are putting 42 psi to them. Is the o2 sensor new?

 

Thanks for the reply.

The O2 sensor was retained from the Monte, so I dont know how old it is...very well could be stock yet, but has never set a code so I left it be.

The fuel pressure reading was done when I had the original injectors in, so Im not sure what its at now....not sure if that makes a difference or not.