Firebird Nation banner
1 - 10 of 10 Posts

·
Registered
1995 Firebird Trans Am, 5.7L 350ci, 4l60e.
Joined
·
109 Posts
Discussion Starter · #1 ·
So I have my car up and running good for the most part. Been driving it for months now but I'm still having some issues i'm having trouble figuring out. The IAC being maxed out but its not really effecting my idle. I've replaced the IAC with no success, and reset it with shoebox method with no luck. Also my B1 LT fueltrim/BLM is 135 while the rest are 128. I plan on upgrading my injectors to 36lbs injectors real soon but idk what this 135 number means exactly and why its different. Also the car exhaust stinks, it used to give a code for lean exhaust until i changed the O2 sensor. Sometimes the car will take off really fast when i hit the gas and other times its not as fast i don't why that is either.

No codes have come up, its just the scan data that shows problems.
 

·
Administrator
Joined
·
15,264 Posts
The PCM reads the MAF sensor and figures out what injector pulse width will supply the exact amount of fuel to maintain an air/fuel ratio of 14.7:1. The feedback from the O2 sensor tells the PCM if it got the A/F ratio right. If it did, the BLM (also called the long term fuel trim = LTFT) will stay at 128. But if the A/F ratio was too lean, and that condition persists, the PCM will start increasing the BLM.

The BLM is a multiplier to the amount of fuel that needs to be supplied. A 135 BLM means the PCM is multiplying the fuel amount by 135/128=1.055. In other words the PCM is supplying 5.5% extra fuel to keep the engine from running lean. From my experience anything within plus or minus 5% is acceptable.

To complicate matters, each bank of the engine is controlled independently, and there are 19 different stored BLM's for each bank. 16 of the cells (0 to 15) are defined by a grid with RPM on the X-axis and engine load (MAF) on the Y-axis. Then there’s Cell 16 for idle, Cell 17 for decel and low load open loop, and Cell 18 for certain closed loop situations and for open loop driving.

Hence the numbers you have published are meaningless without knowing what Cell they are in. To really understand what the possible problem may be (if there even is a problem) you need to look at the BLM's for as many cells as possible. The INT (also called the short term fuel trims = STFT) are relatively unimportant, because they are changing very rapidly for other purposes, primarily making the cat converter work.

I have more detailed explanations I this document:

 

·
Registered
1995 Firebird Trans Am, 5.7L 350ci, 4l60e.
Joined
·
109 Posts
Discussion Starter · #3 ·
My cat is deleted. Also my EVAP and EGR are deleted as well. In the process of deleting EGR the tuning has the "special cells" no longer being used.

I'm interested in the IAC count being maxed out.

My car also stalled when i was backing down a hill the other day for first time, so maybe i need to check fuel pressure?

Will you take a look at scan if i do the process again?
 

·
Administrator
Joined
·
15,264 Posts
Didn’t I already give you info on the IAC? This all sounds very familiar, like maybe you sent me a Scan9495 data log a while back? Or am I confusing you with someone else?
 

·
Registered
1995 Firebird Trans Am, 5.7L 350ci, 4l60e.
Joined
·
109 Posts
Discussion Starter · #5 ·
Didn’t I already give you info on the IAC? This all sounds very familiar, like maybe you sent me a Scan9495 data log a while back? Or am I confusing you with someone else?
I gave you a data log but never got back to me on it. You said the IAC was maxed out and MAP looked a bit high but you needed to look at stuff.

As far as what you told me about the IAC I did it all and it's still at 160. I haven't checked it while driving, but I can get a real scan for you now that I've been driving the car, the last one I sent was just idling.
 

·
Administrator
Joined
·
15,264 Posts
At this point I've stopped reviewing data logs because it often produced results like this. Frustration by both parties. In any case, wouldn’t it be a good idea to go through what you did to try and solve the problem, based on my recommendations? That would prevent others from making similar recommenrations for fixes you have already tried that didn’t help.

I'll go back and review my correspondence. I thought I left this by indicating I had no further ideas on how to solve the IAC problem.
 

·
Registered
1995 Firebird Trans Am, 5.7L 350ci, 4l60e.
Joined
·
109 Posts
Discussion Starter · #7 ·
That's fine you've helped me plenty and I appreciate it. I will post what I tried and did to fix my issue.


You previously recommended 32 or 36lb/hr injectors but it appears the websites you mentioned are out of those sizes. I was wondering if these were good. I believe they are rebuilt Bosch injectors.
Tool Font Auto part Engineering Metal
 

·
Administrator
Joined
·
15,264 Posts
Never heard of the company, no way to tell if those are even genuine Bosch injectors. There are so many Chinese counterfeits of the Bosch injectors that it makes it impossible to know, unless you find an established dealer with a good reputation.

Their website claims 20 years experience, Google review look OK, but I have very little confidence in Google reviews. Too easy to fake. This is a very reliable bulletin board for F-Body info:

 
  • Like
Reactions: EliteKane

·
Administrator
Joined
·
15,264 Posts
The last Scan9495 data log I have is dated 05-25-2022. Is that correct?

If so, there is only a few minutes of idle time - nothing else. That was where I stopped, because I couldn't see any issues related to idle. As I recall, you have had problems in the past with the aftermarket throttle body. You have had problems with accel cable linkage/cable. You tested the IAC motor per Shoebox's procedure and found it to be OK. I believe you cleaned the IAC pintle.

Did you try opening up the blades using the throttle stop? Your TPS volts are approaching the "high" side. There's a limit to how far you can open them without reaching the voltage that sets a code. Next thought would be the IAC passages in the baseplate of the throttle boy are plugged. Or maybe the passage in the throttle body. I've seen one case where coolant was leaking into the IAC passage and blocking flow. I believe you deleted the throttle body coolant flow????

The PCM goes into closed loop at 206 seconds which is the normal time-out from startup. The coolant temp is only 100-degF at transition, both O2 sensors indicate "ready". But the "fuel trim enabled" flag does not switch from "0" to "1" (until the end of the log, 1.7 minutes after closed loop) so the PCM is not capable of adjusting the long term fuel trims (LTFT). The short term fuel trims are compensating as best they can, with the left bank dropping as low as 113 (reducing fuel by 11.7%) and the right bank going as high as 140 (adding 9.4% extra fuel). There are cases where the left and right bank O2 sensor readings go lean, staying there for several seconds. Either very slow O2 sensors or some other problem. The sensor reading should be changing rapidly, several time per second, swinging back and forth from rich to lean. But none of that has anything to do with the IAC counts. Just a sign of additional problems. Maybe new injectors will help. But the picture is limited, with only idle date being supplied.
 

·
Registered
1995 Firebird Trans Am, 5.7L 350ci, 4l60e.
Joined
·
109 Posts
Discussion Starter · #10 ·
Yes thats the only scan log i sent.

I replaced the Traction Control ASR motor because i was told it wasn't working properly by mechanic. That fixed the problem with the throttle cable. He did open my TB blades a little bit to get the idle steady which has worked so far.

Yes i did the TB Coolant bypass. I've thought of going back to the stock TB is that bad idea? idk how much that would hurt performance if it will at all. Do i need to slot my TPS to get the voltage down or is it ok where it is?

I did have to replace my passenger side O2 sensor shortly after because code #64 came on and that was fixed by replacing the sensor.

I thought i was still having issues with fuel because the exhaust really stinks at times, but idk if thats because i deleted the EVAP or not. I also read it could be running too lean causing the smell because it doesn't smell like unburnt fuel, but i get no codes that indicate that. I know that certainly the stock injectors are too small for all the mods i have.

Can i send you another scan doing the procedure with the car now driving?
or should we wait on getting the new injectors first and see? I ordered them and contacted Moe about adjusting the tune.
 
1 - 10 of 10 Posts
Top