Detonation After Injector Upgrade And Tune Up.

[7-UP BILL]

Gentlemen. I have a '90 LX that is somewhat modded. Vortech S-Trim, Edelbrock heads, Gt-40 intake and a fairly tame Isky cam. It was cut on a 114 LC for the SC. It had 30 LB inj and a Pro-M "bullet" MAF. I was able to get 42's and a newer Pro-M for a very decent price this winter. After R/R injectors, I did some maintenance, plugs, wires and C/R. Plugs are 3923's and were burning real nice. "Light grey". BTW, old plugs were 15 years old. Car has 45K on body and 20K on mods. I did notice my conical filter (K&N) was pretty dirty so I cleaned it with their kit. It had a dark oily film on it. Vortech runs the line from the oil fill tube to the filter box for some reason. Now, the engine is getting "air" and when I somewhat "hit" the throttle, I hear that dreaded detonation now. I have a 255 "intank" and a T-Rex. I had the timing set at 10*, but lowered it to 8* and bumped my boost retard to 3. Still detonating. Does anyone have a direction I can start to go to remedy this. Thanks in advance.

 

[mikestang63]

I would highly recommend you get the car dyno tuned before you damage the motor, blower . Detonation is caused by too much timing or its running too lean. What is your FP set at? Is your fuel pump, regulator and injectors all working. What is your A/F ratio? What is your spark gap ?do you have an aftermarket igniton. Are you running premium fuel. how much boost

Not sure what you mean about the motor getting air. The breather tube needs to run to the airbbox before the MAF so you venting the crankcase properly. I assume you are running a PCV valve still and no catch can.

The oil on the K&N is because the filter was dirty Do not over oil the filter.

 

[7-UP BILL]

I know what detonation is. My FP is 40 and goes to about 45 under a light load with an FMU. I have an MSD boost timing master (analog). Plugs were gapped at 35. The oil on the filter was black, not the red K&N oil. My comment on "getting air" was meant to mean the filter is now clean. It's only pinging if I hit it somewhat hard. I've tried to pull codes but I get nothing. Now a 5-speed orig. an AOD. Neutral safety switch is disconnected. Never liked them. I'm thinking that with the old 30's and that dirty filter, I was getting enough fuel. Have no idea what the A/F ratio is. ALL my sensors are original. Is there any way to test the MSD? I think maybe the fuel is suspect as it's been in the tank with StaBil since Oct. Full tank. BTW, the heads are O-ringed. Getting on a dyno at $500 w/ a kid in college is not in the cards now. Any other thoughts would be appreciated.

 

[7-UP BILL]

bump

 

[90sickfox]

If I were you I'd get a wideband air fuel ratio gauge. You'd always know exactly what ratio you're running at. Going lean is a no no. Talk to Willie Lynch at dirtydirtyracing.com.

Our cars computers do well with 30lb and below fuel injectors.... above that and a tune is needed. Willie is one of the most respected tuners and I'm sure he could send you a good tune without the car being dynoed. From the looks of it you're not new to this. Hope this helps you out.

 

[2000xp8]

Did it run right before you changed things? If it was fine before and you aren't running different mods, I probably wouldn't have messed with it.

Did you change the disk in the fmu? Been a long time since I messed with one, but i'm pretty sure the 30's and 42's require a different disk.