Short and Long Trim Fuel question
07-13-2005, 08:09 AM
#1
Teching In
Thread Starter
Join Date: May 2005
Location: Houston, Tx
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Short and Long Trim Fuel question Sorry for the newb question but I've been beating my head against the wall on this motor for over a month now. 
I have a 02 5.3 swapped into a rock buggy. It has a Speartech harness and programming. Intermittantly it runs horrible, like it's firing on half the cylinders. It seems like the longer it runs the better it runs.
There are no codes coming up. A friend put a scanner on it and said that the Short and Long trim fuel is in the negative and the O2 Sensors are reading rich all the time.
Thanks in advance.
Dan
I have a 02 5.3 swapped into a rock buggy. It has a Speartech harness and programming. Intermittantly it runs horrible, like it's firing on half the cylinders. It seems like the longer it runs the better it runs.
There are no codes coming up. A friend put a scanner on it and said that the Short and Long trim fuel is in the negative and the O2 Sensors are reading rich all the time.
Thanks in advance.
Dan
07-13-2005, 08:39 AM
#2
TECH Fanatic
iTrader: (6)
Join Date: Jan 2002
Location: Springfield, IL
Posts: 1,194
Likes: 0
Received 0 Likes
on
0 Posts
Try to be more specific about when exactly it runs horrible. You say intermittently, but that doesn't really narrow it down.
Does the problem start while the engine is running?
...while its at idle?
...immediately after startup?
...at WOT?
Does it go back to normal when..
..you shut the car off and restart it?
..after it sits for a couple days?
..you're just driving along?
Kind of sounds to me like it may be knocking from being too rich, but its hard to say without having more detail.
Does the problem start while the engine is running?
...while its at idle?
...immediately after startup?
...at WOT?
Does it go back to normal when..
..you shut the car off and restart it?
..after it sits for a couple days?
..you're just driving along?
Kind of sounds to me like it may be knocking from being too rich, but its hard to say without having more detail.
07-13-2005, 08:48 AM
#4
Teching In
Thread Starter
Join Date: May 2005
Location: Houston, Tx
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by SMOKINV8
Try to be more specific about when exactly it runs horrible. You say intermittently, but that doesn't really narrow it down.
Does the problem start while the engine is running?
...while its at idle?
...immediately after startup?
...at WOT?
Does it go back to normal when..
..you shut the car off and restart it?
..after it sits for a couple days?
..you're just driving along?
Kind of sounds to me like it may be knocking from being too rich, but its hard to say without having more detail.
Does the problem start while the engine is running?
...while its at idle?
...immediately after startup?
...at WOT?
Does it go back to normal when..
..you shut the car off and restart it?
..after it sits for a couple days?
..you're just driving along?
Kind of sounds to me like it may be knocking from being too rich, but its hard to say without having more detail.
I'm trying to get ahold of the guy that scanned it to see what the trim numbers were.
07-13-2005, 11:06 AM
#6
ha damn that is low, may want to check out some sensors if this is something new, like teh o2s or maf, they tend to max out trims when they go. just something to think of before tuning it, which a scanner will show this by logging some parameters, and it may not set an ses light.
07-13-2005, 07:41 PM
#7
Teching In
Thread Starter
Join Date: May 2005
Location: Houston, Tx
Posts: 14
Likes: 0
Received 0 Likes
on
0 Posts
I've read conflicting statements on here of whether 02s can cause a car to mis. I'm running brand new o2s but they are the generic kind. I guess I'll re check them, just don't understand why it clears up after running a while.
Trending Topics
07-13-2005, 09:39 PM
#8
I had the same problem when I put a Z06 MAF on my camaro. The guy dong my tunning thought I was running a MAF calibrated for a camaro. Once we found out what kind of MAF I had he taylored my PCM for it and all was well again.
What's happening is upon warm up you engine is basing the A/F on the MAF(open loop). Yours is telling the PCM it is getting a lot more air than it really is. When it's warm, it bases the A/F on the O2s (closed loop) it adjust the trims to get the A/F close to stoich.
Hope that helps
What's happening is upon warm up you engine is basing the A/F on the MAF(open loop). Yours is telling the PCM it is getting a lot more air than it really is. When it's warm, it bases the A/F on the O2s (closed loop) it adjust the trims to get the A/F close to stoich.
Hope that helps
07-14-2005, 07:14 AM
#9
Originally Posted by thunderdan74
I had the same problem when I put a Z06 MAF on my camaro. The guy dong my tunning thought I was running a MAF calibrated for a camaro. Once we found out what kind of MAF I had he taylored my PCM for it and all was well again.
What's happening is upon warm up you engine is basing the A/F on the MAF(open loop). Yours is telling the PCM it is getting a lot more air than it really is. When it's warm, it bases the A/F on the O2s (closed loop) it adjust the trims to get the A/F close to stoich.
Hope that helps
What's happening is upon warm up you engine is basing the A/F on the MAF(open loop). Yours is telling the PCM it is getting a lot more air than it really is. When it's warm, it bases the A/F on the O2s (closed loop) it adjust the trims to get the A/F close to stoich.
Hope that helps
07-14-2005, 08:14 PM
#10
On The Tree
Join Date: May 2005
Location: North Carolina
Posts: 132
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by 5.3buggy
I've read conflicting statements on here of whether 02s can cause a car to mis. I'm running brand new o2s but they are the generic kind. I guess I'll re check them, just don't understand why it clears up after running a while.
I have seen sensors fail and the PCM not detect it, and it send erroneous signals to the PCM, making it run overly rich or overly lean.