I've made numerous fairly long trips with my 3.4 swap and the best mileage I've gotten in 29.2 mpg. on the highway, and 22.2 around town. the best I got with my stock 2.8 was 32+ on the highway, and 25+ around town. Is that about right, or should I expect better from my 3.4?
What injectors are you running? 15# or 17# ? I and another Georgia Fiero Club member, both with 3.4 swaps and running 17# injectors got 31 mpg on a trip from Atlanta to Asheville, NC and back.
Around town (rural suburbia), I'm down to about 23 with mixed driving in the 28 mpg range.
That means you would get about 30 mpg on a trip. I don't have cruise which will make as much as 2 mpg difference on a long trip. I'm running the stock 3.4 injectors, which are the 17# 'rs I believe!? You are still getting about 2 mpg better than I am though. Not having cruise could account for the lower hwy mileage, but not the low in-town stop and go mileage.
The stock 3.4 Rochester Multec injectors do tend to run a little richer when used with the Fiero ECM. I installed 17# (16.66 lb/hr) injectors that Fuel Injector Connection said were the same as used in a BMW V8 engine. They were a modified pintle which were similar to stock Fiero injectors. Yes, I do have cruise and it was used during the trip.
I had a 2.8 replaced with a 3.4 in my ’88 GT 5-speed in March of this year at The Fiero Factory. At Jeremy’s recommendation, he reused the stock 15# 2.8 injectors, fuel pressure regulator, and stock ECM. I am getting essentially the same gas mileage with the 3.4: around 25-26 mpg with mixed daily driving and about 30-31 on the highway.
Like fierofool said, it may be that the 17# Multec injectors aren’t quite as happy with the stock ECM in your car.
After reading the thread on injectors I might be going the wrong direction with my 3.4 but I'm going to leave the #17's in there and hope I don't have to swap back in the #15's. I did have a chip burned by GMtuners knowing I was using the camaro injectors, maybe that will bring it back in line to work reasonably well. If it doesn't Darth said we'll fine tune it. Funny how a person reads post after post that says you need to use the 17lb injectors that come with that motor and then can read post after post saying something different. Goes to show each engine is different and wth different options on a engine (ported exhaust, modified intakes, miles on engine) there may be no clear cut path to which injector is going to work best.
Okay, good discussion! Here's what I got out of it: We can use the old 15# injectors all right, and probably get better gas mileage, but why did we do the swap in the first place? Wasn't it to get more horsepower performance? So, to get the h.p. performance, we need to use the 17# injectors, as all the swap directions say. However, better mileage is doable if we make the right adjustments...right? The specialized chip stores all say to change for the 3.4, so I do believe that might be the major key! I had not heard of using specialized injectors from BMW, but that sounds like a good idea, but I think I'll go the new chip rout and see what happens. Thanks fellas! I'd still like to hear from more 3.4 swappers, how well they do with a newly designed chip. Any one want to chip-in about that chip, and where the best place is to purchase it?
[This message has been edited by hypo327 (edited 07-06-2013).]
The stock Fiero 15# injectors can cause the 3.4 to run too lean. Eventually it will burn a piston. If you aren't getting a lean code, check your exhaust manifolds with engine running and the car sitting in a dark place.
I spoke with Fuel Injector Connection a couple of weeks ago about injectors for the Fiero 3.4 application and he said that the Denso injectors, part number ending with 941, were pintle injectors and would fill the application. The BMW injectors I got from him about 4 years ago do run a little lean though they're rated at 16.66 lb/hr at 43.5 psi. Those numbers are the flow recommended for a stock 3.4 and the pressure is the stock 2.8 and 3.4 factory pressures. A slight adjustment in the stock chip would solve the lean burn for me, but it's not lean enough to cause any issues for me, so I've not retuned. If you wish to continue using the Fiero injectors, FIC can resize them for you so they will flow 17#.
I've used both the Mustang 19# Bosch and the stock 3.4 17# Rochesters in 2 other applications and they both had a rich burn, again on completely stock 3.4 swaps.
Sinister Performance and phonedawgz are two who quickly come to mind for chip programming. There are others, too.
85GT 3.4 (3.4 injectors) I get 24 in town. On a trip from Lincoln to Gunnision CO. averaged 34 and throught the mountains hit 38 a couple times. I have did tuning on the ecm over the years. Never have got rid of some ping on hotter days and harder accel.