At Cruise: CEL & Scanmaster Knock Count

[jmc1590]

Hey all,
I just ran across a few problems on my Talon tonight and would like the input of the (more) educated masses. For the last month or so since I got the car, I've been keeping it in town, basically back and forth to work. Rarely get over 45. A couple of freeway pulls allowed me to lower the boost setting the previous owner had set. (21 Psi with no visable fuel mods! What the heck...) I got to the point where a setting of 12 on the SBC would no longer throw knock codes on my Scanmaster. Since then, everything has been acceptable, until today...

Had a chance to take a drive to the next town over, about a 25 mile drive. Commute traffic, just about everyone running 65. No obvious problems for the first 15 miles or so. Then without warning, while keeping the speed steady, the knock reading on my scanmaster jumps to 40! CEL pops on as well. I pull my foot off and the CEL goes away, and the knock reduces to 0. Until I touch the gas again, then knock increases, CEL goes on, and I take my foot off the gas. Two or three of these cycles, and everything evens out again. No knock displayed, no CEL. 5 minutes later the cycle repeats.

I got to town and spent 10 minutes driving around, at low speed with no problems. Started to head back and it happened again. Choosing the Power mode or Economy mode made no difference. Trying to use Cruise Control did nothing. (Well, nothing good. But that's a problem for another day...) Again, once I got into town, reduced speed, the problem dissapeared.

Some info from during the drive: Narrowband never stopped jumping back and forth over .5, which is typical. Low Trim seemed stable at 91, Mid Trim at 86 and High Trim at 84. The CEL came on, but never stayed on. The CEL stored in the Scanmaster is 12, which is MAF. (And I believe is from leaving it unplugged after removing / reinstalling the intake. Amazing how fast you remember the little things in a 2 block drive...)

Boost guages (aftermarket, and the digital on the SBC) both show boost sitting right at ~0 at cruise (3000rpm) without my foot in it.

Ideas? Suggestions?

Thanks!

James

 

[GsxMan98]

sounds like u have a bad knock sensor and i wouldnt run that much boost with no fuel mods or maybe bad ecu

 

[jmc1590]

A little more information...

I took the Talon out again today on the same drive I took last week, with an emphasis on seeing what was occuring at the same time the knock went nuts. Much like last time, the first 15 minutes went without issue. That included a drive over the local peak which added load to the engine. On the other side, the road settles into a light grade, which presented no obvious problems. At first.

Same as before, right around 3000 RPM, while holding steady on the throttle, my knock indicator jumped to 40. Pulling off the throttle allowed it to settle back to 0. Fuel trims are in the same area as before: 91 Low, 86 Med, 84 High. O2 trim jumps on both sides of 100, but not by much.

I did find that turning off the overdrive raised the cruising RPM to 4000 and there were no problems. (A minor display of 1 or 2, but I understand that's normal.) As speed dropped and I got closer to 3000, it occured one more time.

Boost during the trip ranged from 6 at the very start, to 2-3 during the drive. At cruise, boost stays right at -7 or -8, unitl I touch the throttle.

I feel a couple of things are related: RPM, temp and throttle position. I am running a MAF-T and wonder if this could be related to one of it's settings. (The fact that the problem sits right at 3K makes me wonder...)

Thanks in advance.

James

 

[scott90gsx420]

Well for starters is the knocl sensor bad?? Reach behind the motor and feel it if its all slimy then it needs replaced.. Also make sure its not loose.. Second do you have any phantom knock such as noisy lifters or rattling under the hood?? Third try changing the settings on there for the 3000 rpm range add some fuel and see what happens.. I doubt its real knock at that low of a load but do it just to check.