HELP, no codes but I'm getting lots of detonation

[howard]

Hello all. I've been trying to diagnose this problem for a week now. Unfortunately, it's a Maxxon dual twister SMEC and my snap-on diagnostic reader can't seem to talk to it. Anyway, it's cal is for a 3 bar map, +40 injectors, G head, 2.5 engine and super 60 turbo. The only way I differ is that I have a ported swirl head and a super 70 style turbo. The mini was running fine about 2 weeks ago, for around 100 miles when it was still cold out but when it warmed up (or maybe it's just coincidence) I started noticing the Check Engine light coming on briefly which means the detonation sensor is sending a signal. A day or so later it started "singing" or whistleing at 1-2 psi boost under part throttle, fairly loud too. Everything appears to be connected and there are no codes. Timing is set at 10 degrees and just sitting and idleing or light driving - it's great. For giggles, I put the stock SMEC back in even tho I have the 3 bar map and +40 injectors. It did run a bit rich, but driveable and my snap on could talk. Again no codes but I could hear the same singing and the snap on showed the detonation sensor signaling 0.4.
I am really stuck so I'd be happy to listen to any input at this stage,
thanx alot,
Howard

[Phreakish]

check to see if the knock sensor is loose, tighten it down real good to be sure its not rattling.

[lametec]

It's possible the timing curves are too aggressive for the swirl head.

[howard]

Wow, Phreakish - great idea! Ya know I was hurrying to get the engine back together and remember that the sensor took a big socket that I had to find - I don't know if I just put it in hand tight or not

Lametec - I was thinking the same thing but it was OK for quite a while. 18 psi boost and all.

My boss is busy so I started thinking of things I'm gonna check tonight;
1. pull the spark plugs to make sure nothings weird
2. check the map sensor voltages with different vacuum
3. bypass the baro-read solenoid and check the map again

thanx guys,
Howard

[Phreakish]

if the stock smec did the same thing with the head, then it might not be. Back down base timing by 4* and try that, see if it goes away. Sounds like something loosened up to me... check the vac line going to the FPR, and maybe do a FP check to make sure all is well.

Good idea checking plugs, that'll tell ya the combustion side of the story. My turbo 'sings' to me too, but it aint detonation (just turbo wail, sounds pretty neat actually... well, more like an ambulance trying to get thru my exhaust manifold!).

couldn't hurt to also check the ignition/cam timing - if the cam timing jumps, it can advance/retard the ignition...

[howard]

Well the detonation sensor is/was definitely in tight so that's not it.
I checked all 4 plugs and they are identical - a light brown with slight silver peppering on one side, and fairly clean and white on the other. Again, these only have maybe 250 miles or so. The silver peppering is probably pieces of my piston, which doesn't leave me with a "feel good" attitude but that's what I'm trying to correct.
The map sensor's voltages are right on target and that's both by itself, and thru the baro-read solenoid so I don't think that's it either.
I checked timing again and it's at 10 degrees so it hasn't moved on me since the other day.
The one big update is that I played with my snap on scanner to find out what computer the maxxon computer is and it turns out to be a 1988 turbo 2 SMEC. Then I started looking at all the sensor outputs and the one that I forgot about is the Air Temp Sensor. I don't have one and the snap on scanner is showing it as 5.0volts or -7 degrees fahrenheit. I'm wondering if that could be the problem.
Howard

[MRBOOST]

It be the cal! G head cals on swirl head motors = not good.

Quote:

Originally Posted by howard Hello all. I've been trying to diagnose this problem for a week now. Unfortunately, it's a Maxxon dual twister SMEC and my snap-on diagnostic reader can't seem to talk to it. Anyway, it's cal is for a 3 bar map, +40 injectors, G head, 2.5 engine and super 60 turbo. The only way I differ is that I have a ported swirl head and a super 70 style turbo. The mini was running fine about 2 weeks ago, for around 100 miles when it was still cold out but when it warmed up (or maybe it's just coincidence) I started noticing the Check Engine light coming on briefly which means the detonation sensor is sending a signal. A day or so later it started "singing" or whistleing at 1-2 psi boost under part throttle, fairly loud too. Everything appears to be connected and there are no codes. Timing is set at 10 degrees and just sitting and idleing or light driving - it's great. For giggles, I put the stock SMEC back in even tho I have the 3 bar map and +40 injectors. It did run a bit rich, but driveable and my snap on could talk. Again no codes but I could hear the same singing and the snap on showed the detonation sensor signaling 0.4. I am really stuck so I'd be happy to listen to any input at this stage, thanx alot, Howard