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fuel issue..need help

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fuel issue..need help

evilokc evilokc
User | Posts: 81 | Joined: 07/10
Posted: 04/25/12
05:50 PM

i put in a powerjection throttle body injection systemi in my truck and it works well. however im having a slight fuel issue im hopeing some of you guys can help me with. it starts and runs great but if i drive it for a while it gets to where it doesnt want to idle at stop lights. it acts like its running out of gas. it will still drive great but if i get caught at a light the idle drops and it will die is left alone. i can put it in neutral and give it some gas and it will be fine and if it does die i can start it right back. i think its a heat issue for a couple reasons. 1) it doesnt seem to happen much at night or early in the morning when its cooler but during the heat of the day it happens in about 20 minutes. 2) my temp gauge isnt working so that just makes me nervous in general 3) when i routed the fuel lines i remember thinking the line that goes into the rear of the throttle body  was a bit too close to the headder. so i was planning on rerouting that one anyway but i didnt think it would cause me any problem. so ideas fellas?  

evilokc evilokc
User | Posts: 81 | Joined: 07/10
Posted: 04/26/12
09:40 PM

i sent an email to the company and they believe its an idle setting issue. so im trying to tune the motor with my laptop. its messy.  

evilokc evilokc
User | Posts: 81 | Joined: 07/10
Posted: 04/26/12
09:40 PM

i sent an email to the company and they believe its an idle setting issue. so im trying to tune the motor with my laptop. its messy.  

waynep71222 waynep71222
User | Posts: 106 | Joined: 04/12
Posted: 04/28/12
09:49 PM

just curious...

sorry for the late answer...  post how its going..  

do you have the tuning manual.. its about 20 pages long...  you need to find the idle air control info on page 15....  

you will HAVE to use a laptop or if it has a display of some kind to look at the idle air control count .. IAC..  with the engine warmed up....    you will also want to look at the section on the TPS...  so you can verify the TPS voltage when the engine is idling with the idle air control valve between 20 and 50 counts...  that the TPS voltage is close to design spec for minimum TPS voltage.. or the computer will think that you still have your foot on the throttle and will not revert to idle fuel control..  the injectors pulsewidth will stay too wide..  probably around 2.1 to 2.4 Ms.. instead of at 1.2 to 1.4 Ms...    

IAC CONTROL - The injection system is equipped with an “Idle Air Control
Motor” that assists in start-up idle speed control and prevents engine stall
on deceleration. The motor controls a valve that meters bypassed air to enter
the engine. The movement of this valve takes place in “Steps”. The total
number of steps the valve has is 130.
C-TEMP BASED IAC BASE POS - This is the base position for the IAC at the
given temperatures. This value should not exceed 23 when warm and the idle
is properly set. (Butterflies)
(A) IAC CRANKING POSITION - When the engine is in “Cranking” mode, the
IAC motor will position itself to the value entered in the “IAC CRANKING POSITION”
It will then “decay” (reduce) the position in steps entered for each revolution
of the engine, after started, down to the value entered in the “C-TEMP BASED
IAC BASE POS”. The value on the C-Temp based IAC position table is the
number of steps the IAC is open for the corresponding temperature.
(B) STALL SAVER - This feature helps to prevent engine stalling. You can
enter a value (RPM) that you want the feature to become active and the
amount of steps you want it to add to prevent stalling when the throttle plates
rapidly close. The decay value is the number of steps per revolution to reduce
back to the IAC position on the C-Temp table.
NOTE: The above parameter usually does not require change.
(C) RPM FOLLOWER - The RPM Follower lets the IAC motor control the engine
idle speed automatically. The follower can be used to make up for different
loads applied to the engine while idling such as A/C and putting an
automatic transmission in gear.
RPM must be less then…: RPM must first be less than this value for the RPM Follower
to activate.
NOTE: Throttle Position must always be less than 2% for RPM Follower
to become active.
IAC Control - With our new and improved IAC controls you easily change
from two different modes: RPM Target and Step Target. RPM Target means
that the EMS will attempt to automatically control your engine idle RPM
based on coolant temperature. You just need to enter your desired idle speed
for each coolant temp displayed. Further IAC control is found under "RPM
Follower" where you can set minimum and maximum step limits based on
coolant temperature. Always be sure to set the RPM threshold 500 to 1,000
RPM higher than your maxium target RPM. In the RPM Target mode the
Stall Saver setting becomes inactive because it is not needed. The further the
actual RPM is away from the target RPM, the faster the IAC moves to compensate.
In the Step Target Mode, the IAC motor will stay in the position you command
as long as the Stall Saver and cranking positions are not needed. In
this mode you must manually set each IAC position based on coolant temperature.
When using Step Target, the RPM Follower parameters are not
After entering your desired values you must click Send to update the profile.
The bottom portion of the window allows you to see the status of the
IAC motor.
• Close Position: is active when the key is off.
• Cranking Position: is active when the RPM is 400 or less.
• After Start C-Temp Decay: active for the amount of time in the decay table.
• Temp Based Operation: IAC function is active when Step Target is selected.
• RPM Follower: IAC function is active when the RPM Target is selected.
• Stall Saver: is active when the EMS reads the parameters entered in “Stall
• Manual Mode: This is used for troubleshooting purposes only.

waynep71222 waynep71222
User | Posts: 106 | Joined: 04/12
Posted: 04/28/12
10:16 PM

if you don't want to play with the lap top....

try backing off the idle stop screw ..   what... yea.. just try it..  then shut off wait 20 seconds and restart the engine..  the idle air control valve needs to handle the idle air bypass..

if you look around the many forums.. you will find that i know OEM fuel injection quite well.. and this is just a version of GM fuel injection..  with roots back to bendix and bosch fuel injection systems..

the idle air control counts are the amount of steps back from Zero... closed passage... 130 counts is as much opening as the idle air control motor can back out..

at normal operating temps.. the idle air control is somewhere in the 25 to 30 range...

if your idle air counts are lower.. the throttle is open too far... and the ECM is trying to slow the engine down...

if your idle air counts are above 35.. and the engine is at operating temp..     your throttle may be too far closed..

if your TPS voltage is too high because the throttle minimum adjustment is too far open.. or is BINDING and not returning to the exact same fraction of a volt when the throttle is closed.. this can fool the computer into keeping the fuel control ready for power... cause you all kinds of issues..  

evilokc evilokc
User | Posts: 81 | Joined: 07/10
Posted: 12/20/12
01:02 AM

havent been on in a long time but wanted to update this. i was able with a combination of laptop tuning and mechanical adjustments to get the truck running great. i have put several hundred miles on it since correcting the settings and its very good. its turned out to be one of if not the best upgrade i have done.