Took the Vette to Fresno this weekend. Fuel mileage went from "before" new injectors 25.9 to 26.2 mpg to 20.2 mpg after new injectors on the trip monitor. Checked actual fuel used/mileage traveled - 21.15 mpg. It seemed like the mileage progressive got worse. Still does not have the "get up and go" it used to have. Also, when accelerating up a hill in high gear, it seemed to shudder slightly as the engine picked up RPM's. Like the trans was slipping. Reset the TV linkage before climbing the Grapevine but I don't think it changed much. Hard to tell with the traffic.
So I checked everything all over again. No SES light, no codes. Fuel pressure rail - 42 then to 40. Running 36#. Vacuum to the FPR 36". Ohms at each injector - 15.1 to 15.3.
New fuel pump, filter, MAF sensor, Coolant sensor, Bosch/Fors injectors, dist cap, rotor, plugs, wires. Rechecked base timing - was set at 10* BTC and re-set to 6*. Have not checked TPS, but I have not disconnected it. Cats were checked and found acceptable 2 weeks ago, but that may have changed after the new injectors.

I'm ready for any imput, ideas, help. . . .

I did checked my stress level here...
http://webpages.charter.net/hkirtley/stress/

I am under stress. . I think I need to follow their directions

Thanks for the help in advance

Subman

Remember the Wave

 

a bump for ya :lurk:

 

same size injectors?
thats odd.
they all holding pressure?
not sure on the 91,havent been following,but the 92+ lt1 autos seem to average 20.
i see 20.2 most the time on the indicator.
somehow the indicators seem to be fairly close,which i find odd since decelerating on engine compression will set the instant average 0n 99 (max).
an earlier post on mpg had quite a few posts and i dont remember seeing any autos getting 26 mpg.
just the 6 spd which has an extra overdrive ratio we dont get with the autos.
that would be frustrating to take a mpg hit AND a performance hit at the same time. aarg is right.

 

I don't know what the OEM injectors are - The Fords I got from fiveomotorsports are 21#. I left pressure for 5 min or so and they hold at 40# I had checked mileage after I first got the car and the trip monitor was pretty accurate. Thanks for the replys
Subman

remember the Wave

 

just for the heck of it,try unhooking the bat cable for a bit and make the computer re-learn.
cant hurt.
:cheers:

 

I had battery cable off when replacing all this stuff. However, a 60 second test would not hurt. will give it a try in the morning. I'm still not convinced that it's not the cats. So that poses another question. My muffler guy will eliminate the precats and replace the main with a hi-flow cat for about $275.00. Seems steep but Gene's in Downey has always done a great job for me. I have quite a bit of resonance now (tips are about 2" short of the rear of the car). Will removing the precats increase sound and/or resonance alot? It is already a little difficult to hear a normal conversation under 75 mph.
Any suggestions or "don't do this"
Thanks for the replys

Subman

Remember the Wave

 

hey ya know you may be onto something there.
at first i was thinking about how youd check for restricted exhaust.
well a vacuum gauge works for that.
with a plugged convertor,muffler,or collapsed inner exhaust tube wall, a vacuum gauge will initially read normal,then rapidly drop off to low or 0 vacuum.
this is old school stuff now so bear with me...
the mileage indicators in these cars appear to be vacuum gauges.not positive if they are but when in instant average mode they sure do act like one.
more vacuum = higher mpg reading (decelerating/engine braking)
less vacuum = lower mpg (under power/w.o.t.)
if your exhaust is slightly restricted due to the cats you probly would see less mpg on the readout.
you happen to have one of those infrared temperature guns in your arsenal? http://www.raytek.com/
they have some models down to 80 bucks now and they are handy for all kinds of stuff.
check your diff,trans,each exhaust port,even the chip on your video card without even getting dirty :)
i use mine alot.pull the trigger,aim the lazer dot,look at the temp readout.
that would be a handy thing for shooting your exhaust sytem to get an idea.
wish i could help on your resonance or parts picks for that.no experience yet with that.
275? if thats just labor then try and get the parts you will like and some others have proven.
try a search for "muffler eliminators",i found some extensive coverage in that string the other day.
:cheers:

 

Thanks for the test , guess I am under stress too :)


Svo Injectors are not rated as same as other brands , because Svo are rated at lower fuel pressure then us chevy people use . I beleve that the stock GM injectors on corvettes are 22 lbs./hr and are rated at 43.5 psi of fuel , so if you use a 21 lbs./hr Svo injector and you have to make it work like a stock GM one you have to lower the fuel pressure . I think that right now your engine is running a bit richer then before that Is why you saw the drop in MPG .

As for the exhoust part , if you have your main cat cloged you should expierince alot of heat inside the car .


Good luck




[Modified by marlon88, 9:28 AM 7/22/2003]

 

i.o.w.-the patient is rejecting the baboon heart. :jester

 

Hi all I'm new here but I've been reading Submans post and its exactly the same problem I am having on my 87 and I've done everything Subman has done but i have replaced the fuel pressure regulator w/an adjustible one & the coil, not to bring up the plugs again but make sure you got the ones meant for aluminum or cast iron heads they are different. well TY for the tips and if there is any thing i can do to help just let me know.
Adam,Import Auto Tech.

 

"make sure you got the ones meant for aluminum or cast iron heads they are different."

didnt realize that. havent found a deadon cross from the ac no. listed in my owners manual to ngk yet.
will dig even deeper now, thanks
:cheers:

 

dont wanna rob ur post or anything, but i got a prob along the same line. i got a 95 6 speed. i drive agressivly but not too bad at all. my mpg thingy says that i get about 15!!! all the time. when i checked it the manual way it was right. so the car runs fine but dang all my gas is gone. is something wrong with my injectors or what? what do you guys get in the mileage dept? like i said i'm no old granny but i hardly ever go wot on the street. any ideas? time to replace em?

 

So I did some checking myself - Owners manual call for AC FR5LS plug on L9 I've been running AC 5 (both before and after injectors). I don't know what the difference is, but someone might. Re-setting the timing back to 6* BTC from 10* made the car run even more sluggish. I am gonna pull the plugs tonight to see if any are fouled or soaked.
Other than that, I'm down to the following potential problems:
1 - cats are plugged (pre-cats and main were ok 3 weeks ago)
2 - ECM needs something
If I understand some of the posts re: Ford injectors are saying ECM needs upgrading to handle the add'l fuel
3 - FPR needs to be replaced with AFPR
I am a bit confused on this point - especially the really technical side of the opinions - Reducting fuel pressure is better for some / increasing fuel pressure is better for others
I really love driving a Vette and would not trade it now, but when it don't run right - - dam it's a pain.

Thanks for the help

Subman

Remember the Wave

 

well,to simplify one aspect of the injector issue,think about the injector funtions.
you have the electronic side which is telling the injector when to open and for how long.
then you have the fuel inlet side of the equation which is designed to flow a certain measured amount of fuel to the cylinder.
the fuel side doesnt care when or how long or even how much fuel to dump in.
thats the electronics job.
alls it knows is it wants its designed pressure there when its gate opens.
if your using ford injectors that were designed for a lower pressure sytem they likely have larger orifices then,say,a gm injector thats designed to have 40 psi pressure.
perhaps with improved air in and improved exhaust out this makes for a sweet running package.
i say that because theres plenty of svo happy camper injector running people here.
so maybe cutting the pressure down to fords normal pressure would cure your problem for now,and then as mods come along you could turn it up?
im just speculating on this.(all of the above).
one note-the other day i had a 98 1500 pickup with a weak fuel pump.had about 20 psi. would not run.died on the road.had it towed in.no start condition.
no codes.
new pump in tank-38 psi,ran fine.
plus when i was cleaning my lt1 injectors last week i noticed that when the pressure dropped to around 30 it would start to die until i cranked the valve in a little more to give it more juice.
i dont think your car will run at 25 psi normally.
be interesting to know if it does with the ford injectors.
hang in there you'll sort it out.
(btw im really not a windbag-just type very fast)

 

Get an adjustable fuel pressure regolator and adgust it to 38 PSI and see how it goes .

Good luck

 

OK - will order today. This leads to more questions of course.
Setting AFPR to 38 lbs. Is this set when you 1st turn on the ignition; after the fuel pump stop running but befroe starting; when the car is running. Right now the pressures are 42 lbs 1st ignition, 40 lbs not started, 36 lbs running.

Thanks for all the help.

Subman

Remember the Wave

 

So I went to pick up the AFPR and --"wrong" - - checked the Holley book and could only find them for LT1/LT4. So now where can I get the appropriate AFPR my L98. See above posts for other info.
Thanks for the help

Subman

Remember the wave

 

heres one http://www.ecklers.com/product.asp?p...8PW9TRF9MC99F6

i think most all the vette aftermarket dealers have them.
you might ask your local dealer service department if theres an oem animal that will fit.
check any local speed shops? it may be common to many "lesser" vehicles (camaros,fbirds etc)

 

I found the AFPR at J&D corvette. They have it stock and are open on Sat. $60.00. Hopefully, this will solve the problem. If it doesn't I guess the options are A) new cat B) ??? Just wondering - what if the IAC is FUBAR. could this cause the problems I have been encountering?
Any help. Please

Subman

Remember the Wave