1991 Poor Gas Mileage after Injector Swap
 

I know gas mileage is not a big concern, however mine has dropped somewhat dramatically since replacing the injectors with 22lb. Bosch III injectors.

I used to get in the mid 20's on the highway and mid teens in the city. Now I'm getting in the mid teens on the highway and single digits to lower 10's in the city. (this is without jackrabbit starts/stops or hard accelleration.)

The car seems to run great and has no codes at the moment.

I just recently replaced:

The fuel regulator because it had holes.

EGR valve because I was getting a code 32

MAT sensor because I was getting a code about that.

Injectors... As I said, because I was in the neighborhood and still had the original stock injectors.

And finally the thermistat to a lower temp. because I live in San Antonio.

I have repeatedly checked all my fuel rail connections, regulator, and injectors for leaks.

Car does not "seem" to be running rich, yet I am going through gas much faster now.

what temp stat?

check your fuel pressure.

Did you reset the ECM after this swap? (unplug the battery)

How are you determining MPG???

I replaced my Ford SVO 24# injectors with the Bosch 3's, and had the same issue.

The lower-end characteristics of the Bosch 3's is MUCH different, and they pour fuel in. I needed to get with Mick Stevens and have it re-tuned, and we are in the middle of that process right now, getting the off-idle tables mapped and working on the mid-range ones now.

He said they are COMPLETELY different than the OEM/SVO style injectors. They are NOT a direct swap without some retuning. They are GREAT injectors, just not a direct swap.

I'd bet if you put a diagnostic tool on the ALDL, you'd see some numbers that were way off kilter.

Also, check for any air leaks...sometimes it's easy to miss...especially down at the intake/runner connection. It's hard to get to those bolts.

Check your actual mileage by hand. Does it match the dash readout? The car may be getting the same mileage but the readout may not be calibrated to the injectors.

If you're going to attribute a HUGE drop in MPG to brand/tech change, why do you think every other B3 owner hasn't complained about the big drop in MPG?

I lost 6+ MPG city when i swapped in the BoschIII injectors last year on my 86 stock L98.

I used to get 22-23MPG city driving....dropped right down to 16MPG one tank after the B3's went in

I check my fuel mileage by hand...not by using the digital dash.

Thanks

I didn't even attempt to check mileage...haven't paid much attention to it in years.

The overpowering smell of raw gasoline from the exhaust was my clue. It ran OK in the mid to upper range, but would stumble & die when I came to a stop.

The Bosch 3's work better in the upper ranges, more like the OEM's, but the idle and off-idle characteristics are VERY different. Mick had to dial it WAAYYY back to get it to idle right. We've (mostly) got the idle & off-idle fuel tables done and are working on the low-to-mid range.

They are a different beast...don't believe the hype they are a straight-up exchange. I don't regret going to them...I really had no choice. SVO's are no longer available so I had to replace them with something, and Bosch makes good stuff.

BTW: My 24# Bosch 3's "really" flow more like 26#. I got them from FIC as a matched set, and have the flow figures for each injector.

So, as you can see it isn't "exactly" a straight forward swap.

I understand they aren't "exactly" the same. But, it sounds like you ended up with a larger injector. And, it sounds like they make most consumers happy. To make a global statement that B3's aren't close enough to avoid MPG problems is what my prior post is addressing.

Neither response to me goes to that subject. (And, from this thread, it sounds like you think the OP should verify lbs/hr on this injectors?)

Possibly...but they ARE 24# Bosch 3's, so one would THINK they flow that but they don't.

The Bosch 3's were DESIGNED for LS series engines. They are COMPLETELY different from the L98/LT1/4's. The way they run their electronics & the way they do their injection is TOTALLY different. This isn't the first time that I've heard problems with a straight swap for Bosch 3's.

And I had a GREAT tune from Formato on my SVO's...ran strong and had all the things you expect from a great tune like good fuel economy as well.

I swapped out SVO's for Bosch 3's and my tune was toast. THAT was the ONLY change!

Then I have confirmation from the TUNER when he got my diagnostic files that what I said is true. Down low, they flood the engine. Upper end they are mostly like my old injectors.

To combat that we needed to COMPLETELY re-tune the motor.

The reason is fairly clear...

Did you know 24# SVO's also flow closer to 26lbs/hr?

Add me to the list.

Actually, mine were flow matched at "slightly" above 24#...

Kinda throws that theory right out the window, wouldn't you say? :toetap:

Why are you trying to shoot the messenger here?

There are 3 other people in this thread so far who've had the same problems of dropping fuel mileage with them.

I have a fairly reputable tuner telling me exactly what's happening based on what we've had to do to get it running, and you still want to say it's something else?

1) I changed injectors...period.

2) My tune went to hell in a handbasket as a result.

3) Bosch 3's DON'T flow the same as the OEM/SVO's we are replacing.

I'll bet if those who HAVE changed them out put a scan tool or DataMaster and LOOKED at the data the car is spitting out, they'll see it is rich in the idle & off-idle sections of the map.

o you have some way of posting your tech info?

FIC has been extremely helpful during this whole process... I've contacted them over the phone and spoken with their tech support, as well as they have contacted me privately on the forum offering advice and support. I'm sure, with their help, this will be resolved. I have NEVER seen a company so dedicated to their product. I'm impressed!

I will be checking the fuel pressure tonight (Hopefully) when I get home to be sure that the new BWD Fuel Regulator diaphram is not giving me too much pressure. I understand it should be right around 40psi. (Please correct me if I'm wrong)
I will also be draining the system again of ALL power by disconnecting the battery and leaving the lights on overnight.

Then I will hook it back up, let it idle again for about 20 minutes, and then see how things end up.

I have not calculated the mileage yet by hand. I will also do that as well as change the gas. I have been watching the calculations on the dash (instant and average). But I will check by hand to be sure it's reading correctly.

I think it is reading correctly because I ran through a tank of gas much faster than I previously had. (but I didn't start measuring it from the beginning)

If I knew what to look for I could...

I have the bin files and the data logs from the test runs for every one we've done so far.

What data do you want to see?

possibly the base that your car should be at compared to the point that its at right now, i have an 87 so the actual numbers will be different but the comparisons of your numbers and the differences would be good to see. or possibly where they were when you started and where you are at this point. thankyou

thank you for keeping this thread updated, I have fic installed in my car , they work fine, but there's been a few threads with this issue and a thread that starts with the issue and continues thru till its resolved with the steps taken to fix the issue would be good tech. for everyone....hopefully we can do this without all the finger pointing, sensless side banter...hopefully.:hide:

Again, what do you want to see?

I'm all new at this programming stuff, and there are a BUNCH of tables in there. It's why I had Formato burn the chip for me when I put this motor in 10+ years ago.

What do you want me to look at? What table(s) do you want to see, and what data do you want from the DataMaster file?

I'm actually new to it also , so I guess the blind leading the blind wont work, and I'm also learning on the data master .:cheers: