[busmup808]

Charger is on. Just have to finish the timing belt.

[05SVRACER]

I've been fighting a problem for a while and want to see if you guys have any input.




My 98 3.4 SC manual falls on it's face and pulls all timing until around 3500 rpm, then it pulls "ok". I do have the URD / split second FTC piggyback.


I thought I was having a knock sensor issue, which I have the GM style external bolted to the head setup and have had that on the truck since shortly after the rebuild and SC install roughly 50k ago. Have installed new sensors, remotely put them in the glovebox covered in foam, and disconnected them. Disconnected resulted in a CEL and pulling all the timing completely.

With all that being said, It's looking like the factory ecu or the piggyback. Has anyone had a similar problem? Any way to test either or send either off for testing / repair?

I'm strongly considering a stadalone ecu, but don't know where to start...

[gamefreakgc]

Originally Posted by 05SVRACER

I've been fighting a problem for a while and want to see if you guys have any input.

My 98 3.4 SC manual falls on it's face and pulls all timing until around 3500 rpm, then it pulls "ok". I do have the URD / split second FTC piggyback.


I thought I was having a knock sensor issue, which I have the GM style external bolted to the head setup and have had that on the truck since shortly after the rebuild and SC install roughly 50k ago. Have installed new sensors, remotely put them in the glovebox covered in foam, and disconnected them. Disconnected resulted in a CEL and pulling all the timing completely.

With all that being said, It's looking like the factory ecu or the piggyback. Has anyone had a similar problem? Any way to test either or send either off for testing / repair?

I'm strongly considering a stadalone ecu, but don't know where to start...

There's nothing magical about 3500 RPM but it could be an open loop/closed loop dynamic. If you are really mashing it, it will downshift to about 3500 RPM and switch to open loop in which the piggyback alters the signals to add more fuel and pull some timing. That makes me think it's not the piggyback and instead you've got a rogue sensor feeding bad data in closed loop. The sensors that could be on the suspect list are:

Mass Airflow Sensor
Ignition/coils/spark plugs (some engines eat spark plugs in 15K miles)
Oxygen sensor, upstream
Throttle Position Sensor (this can fail with no code)

That should get you started. I am not saying these all have to be replaced, just tested. First thing to check is the plugs and not just a visual check. Measure the spark gap. Should be no larger than 0.035" but ideally 0.032". Once you get above 0.035" you'll start to lose power under high boost situations. Once you go over 0.038 you'll start having misfires and severe hesitation under heavy throttle. More than once I've helped a friend with hesitation like this and found out there's a worn out or damaged spark plug.

From there, clean the MAF and test the TPS as outlined in the factory service manual. The O2 sensor is about $50 on Amazon and can be replaced anyway if has never been done and should improve things a little.