rickso84

My 91 L98 recently dropped mileage after an injector replacement. 21 lb Accel injectors were installed after several of mine, one in particular, went bad. My mileage went from to around 30MPG highway to just over 20.

Resetting the ECM (leaving lights on for several housr after disconnecting the battey) as suggested by forum members didn't appear to make much difference in mileage... still getting about 16 MPG average and used to get around 24.

One big thing that's different now is that, since the EGR valve and solenoid have been removed, after driving on the highway for half dozen miles, the SES would almost always come on, triggered by code 32 "EGR System", which I'd expect. Restarting the car would clear the light.

Now that the injectors have been changed, the SES has not come on and no code 32 has been seen. I've has the car for 2 years and the SES almost always came on at some time or another.

What other things could cause this big change in mileage? About three weeks prior to the car dying on me due to the bad injectors, I had gotten stuck in a huge Memorial Day traffic jam for well over an hour and the engine got a little toasty (had to turn the heater on). After pulling off for to eat something an dlet the car cool down, it had trouble starting and stalled a few times but then was fine (until the injectors crapped out). Could that prolonged heat have taken something out?

The car has a mild cam, EGR removed, and Hypertec chip, ignition module, and 160 deg 'stat.

I'm getting frustrated. The guy at the shop is somewhat baffled. I either need to get this fixed or I think I'll be selling the car. THinking of bringing it to a different shop.

Inlove

Are there any other noticeable differences with the car? Does it start, idle, accelerate, etc, like it did before the over heating episode.

rickso84

I don't recall any differences right after the overheating incident but before replacing the injectors, just that the car would occasionally burp, a precursor I think of the injectors going bad. Wish I had checked the mileage immediately after, so maybe could correlate whether the bad mileage started after the overheating or the injector swap. It was about three weeks after the overheating before the injectors died and think I would have notices a 30% mileage drop but then again, don't recall how much I drove in in that three weeks.

After the new injectors, it seemed to be starting and idling okay but didn't run that well. Timing was off a bit, and reset the ECM. Car now seems to stumble in the 1500 - 2000 RPM range when cold but overall seems to drive a little better. Accelerates as good or better than with the old injectors.

Inlove

Sorry I'm coming up blank. All I can think is that something, vacuum hose, wire or something didn't get hooked back up or wasn't done right. It doesn't sound like the engine got hot enough to do damage but you might want to do a compression test to verify that.

89er

How are you measuring gas mileage?

If you are using the digital readout your numbers before and after can be very misleading.

rickso84

Getting mileage using both digital and calculated. My initial half-tank calculation was 16.8 and digital average said 16.4. Next half-tank calculation was 18.9 and digital was 16.8, so can agree with the unreliability of the digital. Due for my next fillup in a few days.

THing is, car was getting digital average mileage of 25 and I believe calculated was 23 or so. Since mileage seems to be increasing, wonder if after the ECM reset will take a while to relearn everything.

87FIREREDRAGTOP

I swapped out my injectors with accell 24's and had to adjust my computer to 37lbs, you might want to check your blm's to see it they dropped.

rickso84

What's a blm and how do you adjust the computer? Given that I'm using the same flow rate injector, why should I have to readjust?

Mekanic

You wouldn't need to adjust the computer, as 22's are the stock size.

Only things I can think of are this.

1: You had a bad injector(s), failing to pulse on occasion, causing an increase in mileage.

2: Your engine isn't liking the iffy spray pattern of the accel injectors

3: the fact that theyre 21 and not 22 is causing a slight lean condition, and making the computer add a lot of pulses to make up the difference.

my bet is on #3

the blur

lots of people have this problem. check out the thread in the tech section. your car is probably not going into closed loop.

Mekanic

I forgot about that!

vette079

Fried the O2 you mean, so it stays in open loop?

coupeguy2001

no, they think because you have a 160 stat it's not getting hot enough. I have a 160 stat, and the only difference is that it takes 10 more minutes to get to 190*. Mine runs at 199-205 on the highway in summer heat of 109*, 212 on city streets in traffic.

rickso84

1: You had a bad injector(s), failing to pulse on occasion, causing an increase in mileage.

* But the car used to get the same 25 - 30 MPG others are reporting and I doubt everyone else has faulty injectors

2: Your engine isn't liking the iffy spray pattern of the accel injectors

* Didn't expect that... do injectors have different patterns?

3: the fact that theyre 21 and not 22 is causing a slight lean condition, and making the computer add a lot of pulses to make up the difference.

* So is the stock injector 22lb/hr? Where would I verify this? Shop claims 21 is stock value.

rickso84

Another thought. Car has no ERG and would always pull an EGR code, typically while warmed up and on the highway. After injectors were changed, no more EGR code. Thinking that coolant temp and O2 are signals that EGR uses, so if coolant temp too low, EGR test won't run and no SES light. Also if O2 bad, may look like EGR is actually good and again not throw a code. I may be stretching here but did have a heat soak event just before injectors went bad so maybe something else did also.

L98

Changed to Bosch injectors (0280150561-D9B) in 2005 because of shorted injector coils. Suffered about 25% fuel penalty after that. Have checked "everything". Replaced plugs, wires, ECM, EGR valve, checked compression, cat backpressure, fuel pressure, checked timing, monitored data such as BLM with Tech1 (ok) and made a tailpipe check with AIR plugged (Lambda= 1.00)
What happens is a very slight stumbling or misfire at light engine load (cruising). Not all drivers would feel it, but I do (and I know what fuel economy and smooth engine I used to have). Could this really be caused by the new injectors? I start to lean towards that but need someone to convince me before I order the original stuff. Could it be anything with the spray angle or pattern? Is there a difference in atomization?

Lost

stevie1dr

I've got a similar problem on my 89. I just changed to Accel 24 lb. injectors after one of the the stock ones died (as well as the car, right in the middle of the street!) I noticed a drastic drop in gas mileage, and a rough idle that jumps from 500 to 8 or 900 and then back,while cold. After warm up it tries to idle at 5 to 600, but is a little rough. I used to get about 22mpg on the highway and 18 in the city. Now I'm lucky to get 15 on the hwy and 12 to 13 mpg in town. Also, I have noticed when I cruise at a steady rpm and let off the pedal, the rpm's sometimes drop rapidly and then bounce back to a steady decline. It feels like I'm backing down in third gear, instead of the steady drop off I used to experience when in 4th. (it's an automatic). Could it be a problem with the AIC control? EGR? The car seems to run just fine and accelerates real nice. I have the following mod's done: Hedman long tubes, 1.6.1 crane rockers, powerdyne blower at 6 lbs boost. (with intercooler and blow off valve) , a hypertech chip and .308 rear end. I also replaced the coil, cap, etc. when the injectors were installed. Timing was set at 4*. At WOT the car goes like a scalded dog! It's the normal driving that has me worried, since it just feels like something isn't quite right. Any thoughts?

rickso84

I'm assuming everyone has reset their ECM after changing injectors? Check for other postings describing this. Resetting the ECM did not help my situation. Trying to determine how to check the BLM and what to adjust if it's too high.

royalviking

Hi, I am new to the corvette forum. I have an 89. I had three bad injectors and replaced all of them with the 22 lb/hr Bosh Gen III injectors. I have the same problem. Fuel economy dropped from 27-29 mpg highway to 20-21.5. I have not done any mods to the engine. My fuel pressure is in spec (I checked it just before changing the injectors). I have noticed that the digital display shows 1 mpg less than actual.

bnio

I feel for you guys. I have been monkeying with these for a long time and it is hard to tell what is happening without some hard evidence sometimes. First do you know anyone who has a wideband oxygen sensor, if so throw it in and check air fuel ratios. If your cruise rpm used to yeild 27-28 mpg and now it is 20 mpg that is a huge diff and you should see it in the afr. There are many more aspects to dive into how these computers calculate the fuel required, but a WBO2 and a scanner should get you to the solution hopefully. Again afr is a ratio so you should see a noticeable decrease in air to fuel if it used to run 28mpg and now it is 20, it will help if a few guys here can give you there cruise afr if they have it from a wideband since I am to lazy right now to figure the chemical ratio of what of afr for 28 mpg and 20 mpg would be, sorry, but it can be done. Good luck.