New 393C running, Won't Rev Beyond ~3500 RPM

[barnett468]

As for the headers, I've read that you can't go too big

Unfortunately whoever wrote that is a moron and you can easily prove that to yourself by simply removing your headers and seeing how it runs then.

In the end' date=' the exhaust ports were 2.1" x 1.95", so I went with 2" primaries for the stroker, which I had seen recommended somewhere.[/quote']
If you search the net enough you will also see 1 7/8" and 1 3/4" "recommended" for this same app.

 

[Casey72]

It has a rough idle, but a "this thing will die at stoplights" idle with too little throttle blade dialed in.

I don't know exactly what you are trying to say here.

I'm just referring to the adjustment of the idle air control. It's done manually by turning the screws to open or close the throttle blades. More opening of the blade reduces the amount of air added by the IAC, less blade opening increases air. The amount of air added is indicated on the handheld and is ideally very close 0 at idle in neutral and 10-20 at idle in gear. More or less, anyway. Maximum is 175.

Too much opening of the blades will push the engine beyond the target idle RPM set by the handheld and the computer will retard your selected idle timing in an effort to lower the idle RPM. Too little opening of the blades leans things out, makes the idle rougher and will cause timing to be increased to compensate.

It's about striking a balance where idle RPM and timing match your settings in the computer, and it's done by turning screws on the throttle body.

 

[Casey72]

As for the headers, I've read that you can't go too big

Unfortunately whoever wrote that is a moron and you can easily prove that to yourself by simply removing your headers and seeing how it runs then.

In the end' date=' the exhaust ports were 2.1" x 1.95", so I went with 2" primaries for the stroker, which I had seen recommended somewhere.[/quote']
If you search the net enough you will also see 1 7/8" and 1 3/4" "recommended" for this same app.

I'm accustomed to folks with unverified or questiinable expertise spouting off about technical matters related to my field on forums, in articles and even in videos. It confuses the amateur. When it comes to automotive subjects I'm the amateur, and there's clearly no shortage of questionable information on the matter. As such, I appreciate your take on things.

 

[jbojo]

General question for my knowledge from the forum

I see lots of mention to increase A/F ratio but don't you want the mixture to be stoich or near stoich for the fuel being used and the altitude? I see a WOT A/F setting of 9 or 10, wouldn't the fuel burn rate be greatly diminished so a drop to 4000 rpm that was experienced be normal? If you want more fuel into the cylinders wouldn't it be done by using more efficient intake/exhaust flow instead? What would be interesting is what the A/F ratio is on the handheld at WOT.

Casey72, I found out about a family issue yesterday after my last post and had to beat feet back to WA so I drove 26 hrs straight to get home. I'll catch up and see if I can make any suggestions.

 

[Casey72]

General question for my knowledge from the forum

I see lots of mention to increase A/F ratio but don't you want the mixture to be stoich or near stoich for the fuel being used and the altitude? I see a WOT A/F setting of 9 or 10, wouldn't the fuel burn rate be greatly diminished so a drop to 4000 rpm that was experienced be normal? If you want more fuel into the cylinders wouldn't it be done by using more efficient intake/exhaust flow instead? What would be interesting is what the A/F ratio is on the handheld at WOT.

Casey72, I found out about a family issue yesterday after my last post and had to beat feet back to WA so I drove 26 hrs straight to get home. I'll catch up and see if I can make any suggestions.

There's clearly no rush at this point due to the need for new items in order for me to continue. Everyone has provided excellent guidance so far, too. I hope your family are well and I'm glad the 26 hour drive was free of drama. Thanks for dropping in and I'll look for your advice.

AFR on the handheld is exactly as commanded when I'm having the problem. I'm really thinking spark now, but someone told me about that fairly early on.

Regarding the AFR changes, they were part of the process of figuring things out. Ideal? Maybe, maybe not, but a good idea. I've been from valve float, through itgnition, across timing and around fuel and air. Folks have been great, with actual SMEs checking in.

 

[barnett468]

General question for my knowledge from the forum

I see lots of mention to increase A/F ratio but don't you want the mixture to be stoich or near stoich for the fuel being used and the altitude? I see a WOT A/F setting of 9 or 10, wouldn't the fuel burn rate be greatly diminished so a drop to 4000 rpm that was experienced be normal?

You set the fuel to where it runs the best and the AFR will be whatever the AFR ends up being when it is all said and done . As I mentioned before, there is no ideal AFR for all apps and not all gauges read the same.

If you want more fuel into the cylinders wouldn't it be done by using more efficient intake/exhaust flow instead?

No, besides that would require changing pistons if the compression is too low and/or installing the right size headers for the app to achieve the best overall amount of scavenging and/or a cam with the right profile that will create the best scavenging etc.

 

[Paul of MO]

Could this thing have a built in rev limiter? Maybe the spec got set/changed/defaulted?

 

[jbojo]

Casey72,

You mentioned that it might be timing issues so Just want to check the setup:

** The rotor is phased 15* opposite normal distributor rotation

** When the distributor was installed with the rotor you set the crank at 15* BTDC and you lined it up to fire on cyl 1. Assuming that you removed the weights and locked the distributor per instructions.

** On the hand held you disabled timing and started the motor and then set timing for 15* with the timing light and then locked down the distributor.

** Enabled timing control so Atomic was now controlling timing. You never have to adjust the distributor from this point on as the ECU will take care of it. You just input the info and the Atomic takes it from there.

Some general info, you probably know this now.

** Making an timing change on the handheld if you change it more than 2* you need to adjust the IAC cnt again. 0 t0 15 with the car in drive and warmed should be good.

** The Atomic uses the IAC motor and timing to hit target idle rpm. So if you see the timing changing on the handheld at idle the IAC needs to be adjusted. Normally the timing should vary 1* from your initial timing that you set.

** For cam selection my cam met the performance cam criteria but the car ran much better with the mild selection. The fuel maps are different with the 2 selections but Mild cam setting generally works the best in my opinion.

** just an fyi, if you use 900 as idle target and 1000rpm idle setting the ECU will begin to add timing after the motor hits 1000rpm. I would use 34* total at 2500rpm for your settings. Your initial timing is included in the 34* total so essentially you will add only 19* more if your initial timing was set at 15* in the ECU.

** I see you are using 10* ported vac so the ECU will not provide any vac adv until you hit 1000rpm so at idle you should see your initial timing at idle on the hand held that you entered if everything is set up correctly.

When you have time again please list the current settings if you have changed them from your last post. Also tell me a little about your motor.

 

[Casey72]

Could this thing have a built in rev limiter? Maybe the spec got set/changed/defaulted?

The FI and ignition box both have rev limiters set at 7000. Doesn't mean they're not having an issue. I'm grabbing a new coil at lunch and I have a new IAC in the mail. I'll try the coil today, but I'm feeling pessimistic.

 

[Casey72]

Casey72,

You mentioned that it might be timing issues so Just want to check the setup:

** The rotor is phased 15* opposite normal distributor rotation

** When the distributor was installed with the rotor you set the crank at 15* BTDC and you lined it up to fire on cyl 1. Assuming that you removed the weights and locked the distributor per instructions.

** On the hand held you disabled timing and started the motor and then set timing for 15* with the timing light and then locked down the distributor.

** Enabled timing control so Atomic was now controlling timing. You never have to adjust the distributor from this point on as the ECU will take care of it. You just input the info and the Atomic takes it from there.

Some general info, you probably know this now.

** Making an timing change on the handheld if you change it more than 2* you need to adjust the IAC cnt again. 0 t0 15 with the car in drive and warmed should be good.

** The Atomic uses the IAC motor and timing to hit target idle rpm. So if you see the timing changing on the handheld at idle the IAC needs to be adjusted. Normally the timing should vary 1* from your initial timing that you set.

** For cam selection my cam met the performance cam criteria but the car ran much better with the mild selection. The fuel maps are different with the 2 selections but Mild cam setting generally works the best in my opinion.

** just an fyi, if you use 900 as idle target and 1000rpm idle setting the ECU will begin to add timing after the motor hits 1000rpm. I would use 34* total at 2500rpm for your settings. Your initial timing is included in the 34* total so essentially you will add only 19* more if your initial timing was set at 15* in the ECU.

** I see you are using 10* ported vac so the ECU will not provide any vac adv until you hit 1000rpm so at idle you should see your initial timing at idle on the hand held that you entered if everything is set up correctly.

When you have time again please list the current settings if you have changed them from your last post. Also tell me a little about your motor.

Everything is as you describe. Frankly, I picked up a lot of what Ibe learned about making the Atomic work by reading your posts, so it's unlikely that I'd have things set much differently. My settings are the same as they have been, but I brought fuel for WOT back to 11 for now, 20 timing at idle, 34 total at 2500 and no vac advance. Cam is Performance, IAC is not playing well and pegs out when I drive it and come back to idle.

The engine is a 393 Cleveland, 4V heads, Weiand X-celerator, Hooker SC headers with 2" primaries (for which Ive been called, lol), 10.4:1 compression, 242/248 @ .050" and .659"/.666" lift. It's about to get a new MSD coil from the speed shop. It's the only thing left as far as I can tell and it was suggested early on, but I tuned instead.

 

[tony-muscle]

If AFR is suspect, is there a way to know if the oxygen sensor is measuring correctly? I understand you are not getting a fault, but could it be slightly out of calibration? If the sensor is off calibration or slow, it then will completely throw off the EFI unit.

If timing is suspect, can you hook up a timing light and check timing as you approach the troubled 4k rpms. I can't remember if this was already done or was it suggested.

I know in my business a lot of problems are caused by instruments that are not really measuring correctly. A lot of time is spent troubleshooting a matter with no success and in some cases it comes down to a faulty instrument.

 

[mjlan]

I have no experience with the MSD EFI setup that you have, but I think you mentioned that it seems to run great at anything other than WOT- is there any TPS calibration that could be out of whack?

I'm assuming that the Atomic has a TPS sensor? If not, ignore me and carry on...

 

[Casey72]

If AFR is suspect, is there a way to know if the oxygen sensor is measuring correctly? I understand you are not getting a fault, but could it be slightly out of calibration? If the sensor is off calibration or slow, it then will completely throw off the EFI unit.

If timing is suspect, can you hook up a timing light and check timing as you approach the troubled 4k rpms. I can't remember if this was already done or was it suggested.

I know in my business a lot of problems are caused by instruments that are not really measuring correctly. A lot of time is spent troubleshooting a matter with no success and in some cases it comes down to a faulty instrument.

To my mind it was all suspect. But not now.

 

[Casey72]

I have no experience with the MSD EFI setup that you have, but I think you mentioned that it seems to run great at anything other than WOT- is there any TPS calibration that could be out of whack?

I'm assuming that the Atomic has a TPS sensor? If not, ignore me and carry on...

The TPS runs 0-5 volts, but I was unsure how to test it. It did show position properly when I pressed the gas pedal, though.

 

[Casey72]

To everyone who suggested a bad coil: you win.

New MSD coil was procured and installed. With much trepidation I warmed it up and took it on the road. On the big highway I shifter into second gear, brought it to 4000 RPM and stomped it. Holy crap! It was a rocket to 6000 RPM where I let off the gas. I did a couple more runs with the same results through the gears. Awesome. It will need minor tuning, I'm sure, but the thing is super quick.

Someone once said that the problem with being a pessimist is that you can never celebrate when you're right. I dont think he mentioned how much sweeter the crow can taste when you're wrong, though.

Thanks to everyone for the help. I picked up some knowledge and fixed my problem, so I hope others have honed their troubleshooting and gotten smarter on something. Also, my mood is much improved from the last few days.

 

[73pony]

That's great news. Glad it is fixed.

 

[tony-muscle]

Bravo!

I took a lot of notes for when I add my own EFI.

1971 M-code Mach 1

 

[Casey72]

I'm pretty stoked about it. After everything in this thread and a long talk with a fellow from tech support at MSD (tech support was great), the only thing that could be turned up was the possibility of a bad coil killing spark. And so it was.

If you get something from this regarding your FI installation then I'll feel less bitter over the frustration. Actually, I'm pretty over the whole thing with the engine now doing good things for me.

 

[midlife]

That's great! I was reading this thread with interest, saying to myself: "Gawd, it's probably something so simple that everyone is overlooking". I was just about to break out the popcorn to see how everything turned out. Good job!

 

[barnett468]

To everyone who suggested a bad coil: you win.

Yes but what about the people that told you your timing was in to early and it was lean so it ran noticeably better after you richened it up? :whistling:

I have worked on over 1,000 cars and never had a coil do what yours dd unless it also made the engine misfire.