That's interesting. I just read about these Bosch III Injectors, they seem to be quite nice, maybe i'll try them. I can see you were using them for some time. Can you say if they're reliable/fuel efficient?

 

Yes, I have the first 91 Vette specific Bosch III's that Jon modified for the 90-91 Speed Density Vettes (No MAF).

They're very affordable, efficient, reliable and have a 3 year warranty with the Best customer service around! At only $169 a set of 8, they're Highly Recommended!

 

Hi all, here is an update. Fuel consumption problem persists - BLM is around 150.

What has been done so far:
- replaced spark plugs and wires
-Fixed some major vacuum leaks.
-Replaced throttle body with TPIS 52mm (the old one was leaking into the shaft from both sides. New one is leaking too, but not that much). Adjusted TPS to .53 volts.
-Replaced MAF sensor and O2 sensor
- Cleaned injectors , i think mechanic mentioned that the fuel pressure was 34 and that the fuel filter looked new, so i didn't replace it)
- reset ECM by disconnecting minus cable. BLM went from 138-140 to 150.

MPG is 14.5-15 when i drive mostly on highways.
The BLM is still high and exhaust smells very reach. It starts with 128 when the car is cold and the O2 isn't reading. Then it goes up to 152 on idle(1000 RPMs) and down to 144-146 on around 2500 RPMs. INT is floating from 131 to 134. The idle is better than before, but still a bit rough and i would say that the car hesitates. The knocks count is around 4 after the start and does not increase (it was increasing fast before, when i had old wires and plugs). I think IAC is opening to 30 or 40, i guess i need to adjust the throttle plates a bit. I can post here more data from the logs.
Also, i noticed that both TunerProRT and WinALDL show that the car is in closed loop at all times - i guess that's an issue.

I had engine stall just once when car was idling, it stopped with service light went on. I checked for the error codes and there were none of them in memory.

Which direction i need to look at? I guess it could be bad injectors spending more fuel, or EGR valve, putting more air into the exhaust pipe to O2 sensor. But i am not sure, because mine is 1986 with O2 on the left side.
I think i will try to check injectors by disconnecting one by one.

 

Why change the MAF if you are not sure that it is bad?

How did you clean and test the injectors? I'd dump the old multec stuff for the Bosch III units anyways. If you don't test the injectors you can clean it but you won't know if that is the problem. I'll bet he hooked up a canister to your fuel rail, shut the pump off, ran the engine and called it cleaned. I don't waste money on that. Also 34 psi sounds low. How is the timing?

I would say that the IAC counts are ok if you aren't running AC. I prefer to see what they are with everything but the engine off and get about 20-30 counts.

Check the counts the way mentioned.

I'd just dump the old injectors since you need new ones if they are stock anyways.

It is the Air Injection Reaction system that dumps air into the cat and at the exhaust manifold near the head when the system is cold and that means the O2 sensor is not reading.

 

Thanks for reply.
Mechanic told me that the MAF readings were low even after they used a cleaner, he told me the figure, but i cannot remember. He tried a refurbished one and it went higher. Maybe he tricked me, i don't know.

Yes that's what he did Btw, I noticed that MPG goes worse if i add fuel injector cleaners into the fuel.

Maybe i will buy the gauge and test it myself.
By the "timing", do you mean one of the parameters that ECM shows when datalogging?

Thanks, I'll do that today.

Ok i will try with the BOSCH III injectors, maybe that'll help.

 

Just lent a fuel pressure test kit.
With ignition on it pumps to 43 psi.
When i start engine the pressure stabilize at 37 psi on idle.
When accelerate, it goes up to 40 for a second, and then drops to 34- 35 and stays there. If I leave the pedal it goes back to 37.
I also gave it a ride with the gauge on. When i drive it shows 40-41 psi constantly.
I guess fuel pump and filter are in good condition.
When i switch off the engine, fuel pressure drops from 43 to 34 in about 8 minutes.

 

Mine has never had any issues holding that pressure. Was the vacuum hose off during idle measurement? Hose should be off to simulate WOT.

 

No, i just connected the gauge, to the fuel rail. So the pressure should not fluctuate?

 

It should hold rock steady at 43 with the hose off, give or take 1 or 2 psi but not that low. Since you had the hose on, we don't know. It does sound a little low to me.

Just because you have a new pump don't mean squat. What was the reason for the change? Was the pressure low because the pump was bad or was it low because your power lines going to the pump was low?

 

Hi guys, just an update. So i replaced Multecs injectors by a set of BOSCH III from Jon. While i was there, i also replaced the EGR valve. First i noticed that i was not getting this rich fuel smell when i started the car. It now runs more smooth on idle. However i have a feeling that it has lost in power slightly.
For the BLM - when the engine is cold it gets to 137 (not sure if it should do that way) and then as the car warms up it goes down to 129 and keeps at that level or sometimes even goes to 125. MPGs are 23 on highway and around 14-15 in mixed driving. So i guess the problem is solved now. Those were bad injectors.