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

[Casey72]

A silly question.... did you reprogram the EFI and indicated you have 393 instead of 351 ci ?

1971 M-code Mach 1

Not a silly question AT ALL. Because I almost did forget to change it in basic settings and had to go back to set 351 to 393.

 

[barnett468]

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ok, you can not check the timing with the vacuum connected . plug it and never connect it again.

post timing results with the vacuum DISCONNECTED.

you are screamin lean . your engine is going to melt . it needs A LOT more gas.

that is a huge cam . i would run a multi fire box like an msd.

what is your plug gap? . it looks way too big . should be around .035" if you have a high voltage coil.

 

[tony-muscle]

Is the oxigen sensor working? The mixture should be automated by the efi brain.

1971 M-code Mach 1

 

[Casey72]

.

ok, you can not check the timing with the vacuum connected . plug it and never connect it again.

post timing results with the vacuum DISCONNECTED.

you are screamin lean . your engine is going to melt . it needs A LOT more gas.

that is a huge cam . i would run a multi fire box like an msd.

what is your plug gap? . it looks way too big . should be around .035" if you have a high voltage coil.

With the naked eye the ends of the plugs are dark tan and had me thinking a tiny bit rich, which is what the AFR shows when running at around 13.8:1 on the handheld. The plug gap is .035 as set when I installed the plugs a few days ago. The coil is run my a MSD 6AL as required for the timing to be controlled by the fuel injection. There is no vacuum advance whatsoever on the distributor. Vacuum advance is handled by the software only based on user settings.

 

[tony-muscle]

What's the AFR as you approach the 4k rpm?

1971 M-code Mach 1

 

[Casey72]

Is the oxigen sensor working? The mixture should be automated by the efi brain.

1971 M-code Mach 1

The WBO2 sensor reads no fault and shows an average ratio of 13.8:1, which is automated.

 

[Casey72]

What's the AFR as you approach the 4k rpm?

1971 M-code Mach 1

It appears to jump around at that point. I need to get a look when I'm not having to handle traffic to see if there's any consistency in what it does.

 

[barnett468]

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give it way more gas.

don't rely solely on the afr gauge.

do the timing test.

you said it does not have vacuum advance but the computer controls the vacuum advance . this is not possible if you do not have a vacuum can attached to your distributor.

 

[tony-muscle]

What's the AFR as you approach the 4k rpm?

1971 M-code Mach 1

It appears to jump around at that point. I need to get a look when I'm not having to handle traffic to see if there's any consistency in what it does.

Video it ... so you can concentrate in driving.

I think something is not right with either fuel delivey, the efi or the oxigen sensor as you approach 4k. Is there a AFR table with an entry at 4k that may be off?

1971 M-code Mach 1

 

[Casey72]

.

give it way more gas.

don't rely solely on the afr gauge . put tape over it for now.

do the timing test.

you said it does not have vacuum advance but the computer controls the vacuum advance . this is not possible if you do not have a vacuum can attached to your distributor.

I'll admit, when going through MSDs instructions for Atomic timing control I didn't see how that stuff could work, but every piece is stripped off the distributor in the process, including vacuum advance. I'll force some AFR changes in the handheld and see what I get.

 

[Casey72]

What's the AFR as you approach the 4k rpm?

1971 M-code Mach 1

It appears to jump around at that point. I need to get a look when I'm not having to handle traffic to see if there's any consistency in what it does.

Video it ... so you can concentrate in driving.

I think something is not right with either fuel delivey, the efi or the oxigen sensor as you approach 4k. Is there a AFR table with an entry at 4k that may be off?

1971 M-code Mach 1

Video should be doable. AFR is user programmable for idle, cruise and WOT. Not so complicated as for other systems, but it can be tweaked. How that holds up is questionable, because once the self-learning took over it went from a setting of 14.0 13.8 in practice.

 

[barnett468]

.

give it way more gas.

don't rely solely on the afr gauge . put tape over it for now.

do the timing test.

you said it does not have vacuum advance but the computer controls the vacuum advance . this is not possible if you do not have a vacuum can attached to your distributor.

I'll admit, when going through MSDs instructions for Atomic timing control I didn't see how that stuff could work, but every piece is stripped off the distributor in the process, including vacuum advance. I'll force some AFR changes in the handheld and see what I get.

ok good . it is too lean at steady throttle and wide open throttle, so i would go up at least 1.5 richer everywhere with the AFR . in other words, if there is a separate circuit to make it richer at wot like a power valve does, make that circuit richer also . you can always turn it back some if your plugs turn black but they wont with another 1.5 - 2.0 in AFR.

then post the timing test after you get around to it.

if it wants more timing, you will need to add it.

you must fix every little thing you find, and after all the the things are corrected, we will have a lot better idea what the problem might be if it still exists . its possible that it may be fine after more fuel and more timing . only testing will tell.

.

 

[Casey72]

.

give it way more gas.

don't rely solely on the afr gauge . put tape over it for now.

do the timing test.

you said it does not have vacuum advance but the computer controls the vacuum advance . this is not possible if you do not have a vacuum can attached to your distributor.

I'll admit, when going through MSDs instructions for Atomic timing control I didn't see how that stuff could work, but every piece is stripped off the distributor in the process, including vacuum advance. I'll force some AFR changes in the handheld and see what I get.

ok good . it is too lean at steady throttle and wide open throttle, so i would go up at least 1.5 everywhere if that makes sense . in other words, if there is a separate system to make it richer a wot like a power valve does, make that circuit richer also.

then post the timing test after you get around to it.

if it wants more timing, you will need to add it.

you must fix every little thing you find after all the the things are corrected, we will have a lot better idea what the problem might be if it still exists.

.

I'm certainly interested in tracking the little things before doing surgery. I have a plan of sorts now.

 

[barnett468]

i forgot to mention . if the valves are floating enough to limit the rpms to 350, the engine would be missing and popping a lot etc.

 

[Don C]

If you can re-map the AFR I would try it at around 12.5 during acceleration. If that helps, you may have to go even richer on acceleration. I agree with Barnett, 13.8 is way too lean. I would also recheck all of the connections, especially the injectors. If you have a problem with a sensor or low vacuum will the handheld show a fault or trouble code?

Have you checked any spark plugs, yet?

 

[Casey72]

i forgot to mention . if the valves are floating enough to limit the rpms to 350, the engine would be missing and popping a lot etc.

It gets noisy when the trouble starts. Rumbling and shaking with a fuel smell at times.

 

[barnett468]

Have you checked any spark plugs, yet?

I had him remove the two front ones and post photos . They are on page 3.

 

[Casey72]

If you can re-map the AFR I would try it at around 12.5 during acceleration. If that helps, you may have to go even richer on acceleration. I agree with Barnett, 13.8 is way too lean. I would also recheck all of the connections, especially the injectors. If you have a problem with a sensor or low vacuum will the handheld show a fault or trouble code?

Have you checked any spark plugs, yet?

WOT is set for 12.5. Idle and cruise are set for 14.0, but have settled into 13.8 over time. Diagnostics will show errors on all the equipment, but it's running clear.

ETA: Yes, plugs look dark tan to me. The camera may not reflect that, as it has some color issues. Turned dark skin to red and purple paint to green just in the last two days. Based on a few decades of dabbling in looking at plugs and header collectors they look good to me in person.

 

[basstrix]

I'll try your suggestions as I whittle away at each approach to the problem, but everything was pulled from an engine with no issues whatsoever and bolted directly to the new engine, except for the PS pump, which is a new addition. Nothing is impossible, but I wouldn't expect a couple days of swapping engines to turn "known good" parts into issues. Fuel pressure holds when the problem arises, so I'm hesitant place any blame there.

I agree with you, it's not likely that a component failed from simply swapping from one engine to another... at the same time, the symptoms are consistent with ignition breakdown and/or fuel delivery.

Best wishes and keep us posted.

 

[will e]

You could always slap a carb on it for a test.