Lean Misfires at 2700-2800 rpm

[DoctorDex]

Originally Posted by cbatters

Next tine you rev the car in neutral, look at the nock sensor and stop immediately if you see that you are getting a high knock count. (Video wounded like extreme detonation.)

Not sure if I understand what you mean about the video being wounded like extreme detonation.

When I rev it in neutral, from time to time when the car is warm, I will see a few knock counts just in the 2600 - 3000 rpm. I may see 1 - 2 knock counts at any one point in time within this range. The total knock sum might be as high as 5 - 6 counts if I add together all of the "little knocks", within the 2600 - 3000 rpm range, I see when I blip the throttle in neutral. Most of the time, I won't see any knock within this range.

The lound noise heard @ ~ 2600 rpm is coming from the exhaust when it is "sport" mode. It sounds almost like a backfire, except I know it isn't because its not coming out of the intake. The sounds gets much quieter, but is still definitely audible with the exhaust in "tour" mode. I think the video quality is poor and the noise is probably louder than it should be in the video because the car is parked in a parkade which is causing the sound to echo. Under load, If I gradually/quickly accelerate through this range it doesn't make the noise, but it will sound like alot like that on decel, once it gets into the 2600 - 3000 rpm range. Maybe this points to spark timing issue?? --> Running out ideas.

[DoctorDex]

The saga continues...

Completed some experiments today trying to narrow down the possible causes for my car's weird behaviour:

Misfires in 2500 - 3000 rpm range:Bought some starting fluid (petroleum ether). Had a friend spray it into the plenum with the engine running. Revved it, in neutral, from 1500 rpm - 4000 rpm repeatedly. Miss occured regardless of whether or not ether was being sprayed into the intake.

Conclusion: Missing is not caused by fuel injectors/fuel injector timing or any other fueling issue. Therefore, we can effectively throw out my idea that there is a problem with sequential fuel injection. This points to a problem with spark or a mechanical issue.

Edit: I am going to repeat this test again but via a different method. After rethinking the experiment, I realized the amount of ether being sprayed in continously while the engine was running would never be enough to power a cylinder not receiving fuel. Therefore, I'm going to retry the experiment using 100% methanol, which will be sprayed when I manually activate the meth injection kit. This should provide more than enough fuel and it will definitely determine whether the culprit is a spark/fuel issue.

Hot start issue: Ran the fuel pump for ~ 1 min, using the check connector, to clear any vaporized fuel from the fuel lines before "hot starting" the car. Car started easily, however, it still wanted to run extremely lean & rough for the first few minutes. If I try and rev it up, while it is running lean, I can't get the rpms above the magic number, yes you guessed it: 2600 rpm.

Conclusion: Vapor in the fuel lines seems to be contributing to the hot start issue. However, I can't fully explain why it wants to run so lean and rough for the first few minutes despite they're being no vapor in the lines. I find it a bit odd that I can't get the rpms above 2600 rpm (the same place I see the miss), which makes me think that the reason its running so lean for the first while is because it is missing and unburnt O2 is dumping into the exhaust.

Next step: Add starting fluid, when it is running lean on hot start, to see if this fixes the problem. In addition, examine both front and rear 02 sensor voltages when it is running lean to figure out which bank is missing and then start systematically pulling plugs to determine if is one particular cylinder is responsible for the miss.

Anybody have any other suggestions or possible tests I can run?

[Darksurfr]

Do you have the "BOV silencer" still installed in the Bubble split tube just past the MAF? If that isn't there thats a big issue. Creates a MAF stall

[DoctorDex]

Originally Posted by Darksurfr

Do you have the "BOV silencer" still installed in the Bubble split tube just past the MAF? If that isn't there thats a big issue. Creates a MAF stall

No, I'm running a blow-thru system. Therefore, I don't use any of the stock piping. My Bov vents to the atmosphere ~ 6 inches before the air is metered using the GM MAF. Thanks for the suggestion though.

[davidm5287]

Has anyone tried testing or replacing the MFI Fuel Engine Control Relay, the relay thats on the passenger side mounted next to the radio and ECU. Just a suggestion since I don't think I read about anyone testing this relay yet.

http://3sx.com/store/comersus_viewIt...dProduct=26912

[DoctorDex]

Originally Posted by davidm5287

Has anyone tried testing or replacing the MFI Fuel Engine Control Relay, the relay thats on the passenger side mounted next to the radio and ECU. Just a suggestion since I don't think I read about anyone testing this relay yet.

Haven't tried it. However, I do have an aftermarket fuel pressure regulator and gauge and I'm not seeing any issues with fuel pressure when the engine is running. The only abnormality I see is that my fuel pressure drops slowly after the car is shut off, which seems to add to the hot start issue.

[DoctorDex]

Amended the first post, so people don't have to read all 19 pages to find out whats been going on. Everything was posted from memory, so please excuse any inaccuracies. If I've missed something, described something poorly or I'm just blatanly wrong, just let me know and I'll fix the post.

[DoctorDex]

Not sure if anyone is even following this thread anymore, but I figured I'd ask anyways:

1. Does anybody with this problem have an HKS DLI or MSD Dis-4 HO?

a) If no, is there any use in trying an HKS DLI? This would be assuming it is some sort of spark-dwell issue (which I think TurboBob mentioned before?).

b) How about a MSD Dis-4 HO, supposedly it increases the number of sparks in the sub 3000 rpm range, which you'd think would also help.

From what I've seen people have reported smoother running in the sub 3000 rpm range with the MSD Dis-4 HO, but I haven't seen anything about the DLI re: low rpm throttle response. Anybody have any anecdotal evidence?

[badass3000]

I dont have one.
I dont think it should be needed.
I am STILL HERE. Wish I could help a little bit more.

[DoctorDex]

I agree it shouldn't be needed. However, I recently started experiencing brutal spark blowout on my rear bank (? change in weather?) and I've been thinking of getting one anyways. Hoping it might be a two birds with one stone sorta thing.