Max Knock, timing pulled.

[AWDfrank]

My cousin's car (91 gst) has been acting really slugish. His car will not idle unless he has his base timing advanced to around 10 degrees.

We used my datalogger on it and the knock was reading the max allowed, 43, and his timing was being pulled to around 5 degrees so theres no need to say it was very slow.

He changed the base timing and I he didn't tell me how he adjusted it, but I assume he lowered it from 10. After this, the knock lowered to 25-35 and timing was pulled no lower then 10-13 degrees.

What could he do to lower knock even more? His boost is at 10 psi and knock occurs while reving and cruising. Could it be a bad knock sensor? How can phantom knock be checked for? Ill have him check for goo on the knock sensor, any other ideas?

 

[gdmbat85]

yea, the only things i could think of are either the knock sensor is bad (my personal thought) or your having phantom knock from lifter tick. only reason i think its a bad sensor is cause its reading full knock. usually if you get phantom knock it doesnt read full knock. goodluck

 

[1gcrazy]

I'll assume you've already adjusted your BISS screw.....
You make it sound like you're adjusting the timing to lower the idle...

 

[JayRolla]

Have him set timing to 5*btdc and do not change it. If it will not idle he has problems else where. Adjust the biss screw. If that dont work the isc may be bad. Also a boost leak test should be performed along with checking TB to see if its sticking, dirty, leaking, or if the cable is binding. His knock is coming from the advanced timing.

 

[AWDfrank]

I talked to him and I guess he only lowered the timing from 10* to ~8*.

Of course we did try adjusting the biss screw for idle, but besides the idle with base timing at 5* the engine revs slow, is slow and still knocks to 43 counts. In other words it is slower at 5* base then it is at 10*? I don't know why this is, it's as if it's opposite of what it should be doing. I suppose he should keep the base timing at 5* regardless of it being slower and fix any other problems he has. Why would advancing the timing make his car faster, but with no more or less knock?

I also think he may have a problem with his isc, sometimes his car will finally idle normally but will raise from 1,000-1,500 rpm. It seems obvious that the ics is the problem in this case, that or idle surge. Could this be a reason for the problem stated in my OP?

 

[4Gmoney63]

What do the low fuel trims look like? When i had horrible boost leaks at the tb my fuel trim was pegged at 140% and it would knock to 43 count when cruising if i let it. Once i fixed the leaks and got my fuel trim back to normal the problem went away.

 

[JayRolla]

List all his mods that he has. That will help. I would check the knock sensor and if you feel some goo coming out its bad.

 

[spyderturbo007]

I would also crack open the ECU and make sure the caps aren't leaking.

 

[AWDfrank]

Low fuel trim is 137.

All he has is a 2g manifold, intake pipe, b/c @ 10 psi and a cheap muffler on the stock catback.

I think he is going to do the caps on the ecu today or tommorrow so we'll see then.

This is for my car, why would all the fuel trims be at 100 only?

 

[JayRolla]

His fuel trim is at 137 and he has no fuel mods. Wierd should be closer to 100. With you car I dont think the 1990's ecu reads fuel trims. I would have him check the knock sensor to see if its bad or maybe loose.

 

[AWDfrank]

Alright, I'll update tonight.

 

[AWDfrank]

Just in case anyone comes across this thread with the same problem, it was a bad knock sensor. Seemed to solve everything and base timing is back at 5* with no problems.

 

[1gcrazy]

Mine is bad and knockin...I've got a spare. Just have to find it...

 

[spyderturbo007]

List all his mods that he has. That will help. I would check the knock sensor and if you feel some goo coming out its bad.

Just in case anyone comes across this thread with the same problem, it was a bad knock sensor. Seemed to solve everything and base timing is back at 5* with no problems.

Good job JayRolla on your diagnosis!