Diacom users
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,630
Likes: 10
From: Drag racing junkie Va.
Diacom users
I just got my Diacom-P installed and ran at the strip this weekend with it for the first time. I'm seeing a 4-8 degree spark retard at
5000-5400 rpm in first gear only (auto w/2600 stall, 3:73s). The knock sensors are new and I had a combo of Sunoco 94 and 102
race gas in the tank, EdWright chip and SLP exhaust. I see the spark counts pegging each time this happens, any ideas where to
look?
Thanks in advance, Dave :flag
5000-5400 rpm in first gear only (auto w/2600 stall, 3:73s). The knock sensors are new and I had a combo of Sunoco 94 and 102
race gas in the tank, EdWright chip and SLP exhaust. I see the spark counts pegging each time this happens, any ideas where to
look?
Thanks in advance, Dave :flag
Drifting
Joined: Nov 2000
Posts: 1,722
Likes: 0
From: Big D Tx
Cruise-In II Veteran
Re: Diacom users (new92racer)
what kinda thermostat do you have in your car, what was your running temps. also, what was your o2 sensor readings around the time of the spark retard.
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,630
Likes: 10
From: Drag racing junkie Va.
Re: Diacom users (88L98)
The thermo is 160, the engine was in the 176-192 degree range over numerous runs, O2 readings were 920-942 mv
and the injector pulse widths were around 9.2 ms.
and the injector pulse widths were around 9.2 ms.
Racer
Joined: Jul 2001
Posts: 399
Likes: 1
From: Toronto Ontario
Re: Diacom users (new92racer)
You're running too rich. My best performance is with the O2 reading around 850-870mV at WOT. Reduce your fuel pressure and your motor shouldn't knock as much + you'll go faster.
Drifting
Joined: Nov 2000
Posts: 1,722
Likes: 0
From: Big D Tx
Cruise-In II Veteran
Re: Diacom users (Eric94)
id have to disagree, my motor seems to be quickest around .915-.920. although, .940 does seem a tad rich. you might just be getting false knock, you could try placing a resistor (3.3k ohms?) from wire on the knock sensor to ground to disable the knock sensor temporarily.
[Modified by 88L98, 2:05 PM 9/24/2001]
[Modified by 88L98, 2:06 PM 9/24/2001]
[Modified by 88L98, 2:05 PM 9/24/2001]
[Modified by 88L98, 2:06 PM 9/24/2001]
Drifting
Joined: Mar 1999
Posts: 1,931
Likes: 1
From: Norcross GA
Re: Diacom users (88L98)
Adding more fuel or less spark advance will reduce the preignition if it is there. I'd suggest you look at the knock signal to see if it is real first. i.e. The disconnect idea's mentioned above. Or maybe just (temp) take some timing out and see if it still detects knock.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
Instructor
Joined: Sep 2001
Posts: 171
Likes: 0
Re: Diacom users (ZylaRace)
Fellas-
In another thread, (a/f ratio dated 9-20) I noted that volt readings by themselves
to determine a/f ratio is of little value. To do so, would result in an a/f ratio being
off up to 1 full ratio. Example: instead of 12.5, it can be 13.5 to 11.5. Exhaust
gas temperature (and variations of same) must be factored in. Any exhaust gas
analyzer manufacturer w/ integrity will admit this. This includes Motec and Autronic,
the 2 I had considered the gold standard in exhaust gas analyzers. This standard
may now include the 'new kid on the block' FJO Enterprises, of which I became fam-
iliar with just recently through the above mentioned thread. They have what could
be considered new technology to factor in exhaust temperature. The bottom line
is, this new technology and its equal accuracy can be obtained for alot less money.
By the way, check out their web site in about 4 to 6 weeks for something new from
them. As a side note, wide band sensors, by themselves, do NOT guarantee anything
in the way of accurate a/f ratio readings! Also, different O2 sensors will cause the volt
reading obtained to vary as well. Hope this helps. A site one can use for reference is http://shared.slowcar.net/o2_volts.xls
In another thread, (a/f ratio dated 9-20) I noted that volt readings by themselves
to determine a/f ratio is of little value. To do so, would result in an a/f ratio being
off up to 1 full ratio. Example: instead of 12.5, it can be 13.5 to 11.5. Exhaust
gas temperature (and variations of same) must be factored in. Any exhaust gas
analyzer manufacturer w/ integrity will admit this. This includes Motec and Autronic,
the 2 I had considered the gold standard in exhaust gas analyzers. This standard
may now include the 'new kid on the block' FJO Enterprises, of which I became fam-
iliar with just recently through the above mentioned thread. They have what could
be considered new technology to factor in exhaust temperature. The bottom line
is, this new technology and its equal accuracy can be obtained for alot less money.
By the way, check out their web site in about 4 to 6 weeks for something new from
them. As a side note, wide band sensors, by themselves, do NOT guarantee anything
in the way of accurate a/f ratio readings! Also, different O2 sensors will cause the volt
reading obtained to vary as well. Hope this helps. A site one can use for reference is http://shared.slowcar.net/o2_volts.xls
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,630
Likes: 10
From: Drag racing junkie Va.
Re: Diacom users (arnold)
I agree with the idea that the car might be to rich myself. I went to the MPC Corvette dyno day a couple of weeks ago and we saw a 10 hp gain when the FP was upped 4-6 lbs. from stock. However, we don't race dynos do we! I haven't had enough track time since then to play the "ABAB test" routine with the FP for et/mph changes. Last Saturday I did lower the pressure by 4 lbs. and noticed a definate SOTP improvement, much crisper throttle response. To bad the battery in my laptop had gone dead by then so I couldn't record the results.
Does the addition of the resistor disable the knock sensor(s)? I've heard that some of the aftermarket chips disable the KS, anyone have this info?
Thanks for all the help and hints so far, Dave :flag
Does the addition of the resistor disable the knock sensor(s)? I've heard that some of the aftermarket chips disable the KS, anyone have this info?
Thanks for all the help and hints so far, Dave :flag
Racer
Joined: Jul 2001
Posts: 399
Likes: 1
From: Toronto Ontario
Re: Diacom users (new92racer)
Adding a resistor of a high enough value( in the MEG ohms ) will definitely disable the knock sensor. What's actually happening when you do this is that you're changing the low pass filter frequency that is in series with the connection to the ECM. A higher value resistor = a lower low pass filter frequency. I wouldn't suggest this because the spectral content of a engine knock contains many higher frequency components. GM has calibrated the low pass filter so that the ECM false noise induced knock readings are minimal.
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,630
Likes: 10
From: Drag racing junkie Va.
Re: Diacom users (vette_tweak)
I found the link today that describes the knock sensor mod to lower its sensitivity, might give that a try. Can anyone else add their O2 readings at WOT to this during a good pass? I was thinking that this is a tuning point for the AFPR but I might have been going the wrong way. I'd rather use EGT but haven't scored one of those units yet. Thanks again, Dave :chevy
Le Mans Master
Joined: Oct 1999
Posts: 9,713
Likes: 3
From: Sachse Texas
Cruise-In I Veteran
Cruise-In II Veteran
Re: Diacom users (94vette)
LT4 knock modules only work with '94-96 computers. Since his is a '92 that will not do any good.
I would say lean it out just a tad. I was running terribly rich with the Ed Wright chip. I found it ran best with between 39 and 42 psi dialed in on the regulator with the vacuum line off. I would not go below 39, nor would I go above 45 or 46 on an LT1.
Are you running SVO injectors? If you are running 24lb SVO injectors, Ed may have it running a little more rich than if you were running a 24lb GM injector. At least that is what I attributed my running rich to.
Other sources of false knock can be heat shielding hitting something or anything else loose that may be knocking around next to the engine. Since you have new knock sensors, did you tghten them to 12-14ft lb? If you tighten them more than that, they may turn out to be more sensitive. Just throwing out ideas.
I would say lean it out just a tad. I was running terribly rich with the Ed Wright chip. I found it ran best with between 39 and 42 psi dialed in on the regulator with the vacuum line off. I would not go below 39, nor would I go above 45 or 46 on an LT1.
Are you running SVO injectors? If you are running 24lb SVO injectors, Ed may have it running a little more rich than if you were running a 24lb GM injector. At least that is what I attributed my running rich to.
Other sources of false knock can be heat shielding hitting something or anything else loose that may be knocking around next to the engine. Since you have new knock sensors, did you tghten them to 12-14ft lb? If you tighten them more than that, they may turn out to be more sensitive. Just throwing out ideas.
Team Owner
Joined: Apr 2000
Posts: 27,818
Likes: 8
From: CT
Re: Diacom users (Vette92)
Chris......
How's the new HEART coming for the Blue Beast? Are you going out and talking to it yet? Hehe. I did that a few times last Winter. It sucks seeing it sit there.
JD
How's the new HEART coming for the Blue Beast? Are you going out and talking to it yet? Hehe. I did that a few times last Winter. It sucks seeing it sit there.
JD
Le Mans Master
Joined: Oct 1999
Posts: 9,713
Likes: 3
From: Sachse Texas
Cruise-In I Veteran
Cruise-In II Veteran
Re: Diacom users (JD 90 383)
The heart is still being worked on...very long and tedious process. Pistions should be in this week which puts the small block together next week. Having some head work done too so it looks like maybe 2 weeks I will go pick it up hopefully. I will probably have it all ready by Christmas ;). :crazy:
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,630
Likes: 10
From: Drag racing junkie Va.
Re: Diacom users (Vette92)
Chris,
I still have the stock injectors at this point, but I will back off the FP this weekend. Thanks for the tip on the heat shield, and the knock sensor torque, I'll look at them this weekend. :yesnod:
I still have the stock injectors at this point, but I will back off the FP this weekend. Thanks for the tip on the heat shield, and the knock sensor torque, I'll look at them this weekend. :yesnod: