Working out issues, need some help/advice.

**beamsjr** · 12-01-2016

I have installed a tbi system from a 4.3 on my Jeep with a 258 4.2. I have it running but I am having some issues that I just cant figure out. It is currently running off of the tach signal and is not controlling timing.

1. When you first start up, it idles great. After a few minuets it does a weird surge thing every minute or so. Looking at the log, it looks like computer is receiving info that the motor jumps to 1800-2000 rpm, although the motor defiantly did not. The computer appears to attempt to compensate for this and lowers the rpm, which brings the motor down to roughly 400 rpm and then it corrects its self. It repeats this behavior every minute or so. If I disconnect the IAC this issue goes away. I have purchased a new IAC and it does the same thing.

2. After the motor Is nice and hot, after putting in gear and waiting a minute or two, the motor begins to stumble and then stalls. After it stalls it is then unable to start for about 10 minuets. I believe there is no spark at this time, which seems to me like it would be the ICM overheating. I have tried a few different ICMs and they all seem to do the same thing.

3. Knock sensor error code being thrown. Knock sensor error counts in the 5000 range, Does not sound like there is any knock to me... The knock sensor is new, so I'm not sure what that is all about.

Any help would be greatly appreciated.

**babywag** · 12-01-2016

For the random rpm issue, use a twisted pair of wires for magnetic pickup.
I saw random crazy rpm spikes until I did this.
Easy to try just make a set and install them.

I'd remove the knock sensor and module and tie 5v to ecm wire.
You'll never get good reading due to different engine harmonics.

Post your log files and maybe it'll help with other problems.

EDIT: Did you do the initial setup? This is a mandatory thing...
below snipped from thread http://www.gearhead-efi.com/Fuel-Inj...ull=1#post5091

2. IAC reset/min idle speed- This sets the throttle plate on the throttle body to a specific rpm. It should be set to 100-125 RPM below idle commanded in bin file. At ALDL connector you need to put a jumper between pins A and B of the connector. These are pins A9 (what/blk) and A12 (blk/wht) on the ECM. This puts the ECM into ALDL mode. Turn the key on (not start) and the IAC should drive completely closed. You will normally hear a buzzing from the IAC. If you have the TunerPro running up and running on your laptop, or a Scan Tool you should see the IAC went from 145 to 0. Now unplug the IAC connector. Turn the key off. Remove jumper. Start motor. If the idle is too low you may have to keep it running. On the front drivers side of the throttle body is the adjustment screw. It will probably be behind a silver plug. If so just use a drill bit slowly to drill a hole, not to deep as to damage the torx screw behind it, just enough to use a punch to grab it and remove it. Then use a #20 torx bit to adjust the idle speed to at least 100 rpm less then your warm idle speed in bin. If 600 then set to 500 rpm. You are looking for the lowest consistent idle your motor will do. When set, turn off motor and reconnect the IAC. I try to keep the IAC count to at least 10-20 with the motor warm and idling. Higher number are OK but more air pushing gas past throttle blades on TBI engines is better!

3. TPS Throttle Position Sensor. With the idle set, you need to set the TPS idle voltage. This need to be set to about .54V to .60V
The TPS is on the passengers side and will have 2 screws holding it on. The factory TPS will not have much room in the holes for adjustments so I use a drill bit or file to elongate the holes as needed. Or bend tang on throttle shaft. To adjust, just loosen the screws and twist the TPS. You can monitor the voltage on Pin B of the connector with the key on or at pin C13 of the ECM. You can also see it in TunerPro or Scan tool! Anything away from .54V will also show as a percent of throttle on 1227747 ECM like .2 percent or 1.7 percent...depending on how far from .54 you are. But otherECM/PCM set to 0% when key on. I try to keep the idle setting to within 1 percent do to settings in bin file.

This is also a good time to check your TPS voltage. Once it is set, just watch the voltage as you open the throttle. you should see a steady rise in voltage up to about 4.5-4.8V at WOT-wide open throttle. If it jumps up and down or skips some then you will need to replace it.

4. Fuel pressure The systems calculates the fuel needed based on the initial settings for injector size at a specific pressure. If the pressure changes then the fuel calculations will be off. I recommend checking the feed and return line pressures at the very beginning. This can save a lot of time later. The pressure on TBI should be 13 psi and 43.5 on TPI/MPFI with stock regulaters.
These are feed side pressures and should not change with rpm or load.

The return should be near 0 psi.

These are basics that need to be done before any tuning or data logging can begin.

**beamsjr** · 12-15-2016

Thank you very much. Twisting the pickup wires worked great for the idle. I found the return line was clogged, took care of that and I am running great. Thanks again for the excellent advice.