91 Q45 Timing - Bad at 15º - Good at 20º Better at 25º ???

[trw2k]

The car has been running great since fixing codes (12 MAF - 32 EGR - 34 Knock sensors - 53 Exhaust Gas Sensor)
Fixing the vacuum lines and pulling a ball bearing out of the EGR tube fixed all of them.

SO Today-
I have never set the timing on this car so figured I should check it.
I followed the instructions at http://www.q45.org/checktiming.html - went with the technique in "B".
The timing was 25º BTDC actually it was even a bit higher. Like I said this car has been running great at all speeds.
I set it to 15º (4th notch from the left) - Idle at 650 took it out and all though it idled and ran smoothly under gentle acceleration it had NO power under medium to heavy acceleration...like NO power flooring it.

SO I set the timing to 20º and it was much better...

This thread reports something similar but it is never resolved post4571722.html?hilit=q45%20timing%20q ... s#p4571722

This makes no sense to me...any ideas as to what is going on?
..Throttle Position Sensor?
Is it ok to just time it to what it runs best under and forget it?

...is it possible that the cars electronics have compensated for past errors and is now set to run at 25 BTDC?
If so, is there any way to reset it all to a default running configuration?

Tim

[Q451990]

Did you unplug the AAC valve?

Heath

[trw2k]

Thanks Heath - I did disconnect the AAC but I didn't disconnect the Throttle Position sensor (according the above mentioned link) so I will try that today.

When I do disconnect the AAC I don't always see a drop in RPM. I have recently taken it out and cleaned it though.

I was reading about the effect a bad knock sensor can have misfire-driving-me-nuts-please-help-97- ... r#p2468611
The knock sensors sending the message to the control unit of knocking and the control unit retarding the timing to eliminate the knocking. If I reset the ECU and the code doesn't come back does the timing reset back to pre-knocking timing?


I drove the car to work today and it runs great at 20BTDC...but...

[Q451990]

Not sure... I haven't messed with the timiing much. The knock sensors will retard the timing advance, but I don't know how much of that takes place at idle.

Heath

[trw2k]

Thanks Heath for being willing to help out everyone!

Turns out I do have a bad knock sensor. I didn't know that a bad Knock Sensor won't make the check Engine light come on.
I might try bypassing the knock sensors with the 470k ohm technique just to see if the engine timing changes.

[trw2k]

Alright this mystery is solved.

The knock sensors were both non-functioning.
The ECU sensing this retarded the timing about 10º.
Someone at some point in this cars life set the timing to 25º BTDC to adjust for this.

I first cleared the code 34 from the ECU. As I learned, a malfunctioning knock sensor code 34 does not trip the check engine light so I wasn't aware that I had a code 34 until I checked.

I started the car as it had been running (25º BTDC)...warmed it up and set the timing back to where it should be at 15º BTDC.

Then I tricked the ECU into thinking there were two good knock sensors installed (found elsewhere in the forum) by putting a 470k 1/2 watt resistor into each knock sensor connector & connected up the Engine Temp Sensor connectors (otherwise it would throw a code 13) and started the car.


It started right up.
I took it out.
It ran great without throwing any codes

Now I get to pull the plenum and change out the knock sensors

Tim

[Q451990]

Now I get to pull the plenum and change out the knock sensors

Fun for you!

Nice troubleshooting, and yes - the knock sensors do need to be functioning. Dennis (Q45Tech) mentioned in one of his posts, that the ECU must check for more than just the proper resistance at startup, because even with the resistor trick, the timing maps are off eventually.

Heath

[squeefoo]

Thanks for the update !!

When I replaced mine I replaced the crusty crinkly coolant hose.
I aimed the hose clamps so you could check then with an extension once in a while by sticking it through the upper plenum runners. Just set the plenum on top and eyeball it up.