1993 F250 351W, E40D, 2WD.
Hey yall, long time no message. Its been a minute but I had finally installed my new motor, and she runs great. Lots of power, no oil pressure issues this time, she stays cool, awesome! Just a slight drawback that I am trying to diagnose right now.....she dies.....nearly every time she comes to a complete stop....and only in drive. If I switch her to neutral right before coming to a complete stop, zero issue. And she will idle all day in park with no issue.

Some things that I know, vacuum reads right around 16 when idling, I knew this cam would have lowerish vacuum because it technically was not meant for efi. However the specs were close enough that I was willing to risk it (Edelbrock #2182) (specs will be listed below). And I know she has the tiniest of vacuum leaks that I am trying to narrow down right now (she slightly deviates just below 16 every 9 seconds or so (rpm lowers when it happens).

This does not feel like a fuel issue.

My hypothesis right now is that she does not produce enough vacuum, and so when I press the brakes and the booster draws in vacuum its to much for the engine to handle and stalls out? I do not even know if that is possible, but its my best guess right now. However at the same time my drive way is at an angle, and because of that I am able to slowly stop with minimal pressing the brake pedal and she does not die (at least not usually). And because of the incline I am able to leave her in drive without her moving forward, and when I press the brake pedal when she is in drive but stationary she does not die. So this only happens when she is moving and then stopping? Which kinda shoots my hypothesis in the foot.

The only thing I have really checked beyond everything else I have said is the iac valve. And all I did there was unplug it, and she showed a vast difference in rpms and behavior so I plugged it back in.

It will be a week before I can work on her again, and I would like to keep in mind what everyone else's thoughts on this problem might be.

I do appreciate any thoughts towards this, I have thought about buying a vacuum canister for the brake booster, but I do not like throwing parts at a problem that I do not fully understand yet.

Thank you to all who can try and help!

 

Summit's listing states that cam is not EFI compatible:

https://www.summitracing.com/parts/edl-2182

Given your symptoms, I would agree with that.

 

Well in my defense I had called Edelbrock before purchasing it and talked to their "specialist". On paper we both agreed it would meet the bare minimum required for an efi system, he mentioned from his notes of the cam that the reason it was listed as "non-efi" was due to the fact it was not built for, and was not tested on an efi system. I had ran the cam specs through desktop dyno, and I liked what I saw. That and I could not find any other cam that could match or exceed it while keeping the efi happy with vacuum (if you know of a better one, please let me know!). If that's the issue, then live and let learn. Im going to leave the house in a little while and try to find an empty road, disconnect the brake booster hose, and try to come to a hard stop (at least as hard as a stop one can make without a booster). And see if the issue persist.

Thank you!

 

Update, I do believe I have narrowed it down to the cam not providing enough vacuum. I did 3 stops with the brake booster unplugged, she stayed running every stop. The other 3 with her plugged in, she died every stop. Welp, I guess I will be ordering a vacuum canister. I will keep you updated once I get it!

 

I suspected the cam was on the edge for working with the factory Speed Density system. Your stated vacuum at idle is a clue. One thing to verify is the base timing with the SPOUT plug out. Retarded timing influences vacuum to the lower side. You may be able to bump up the base timing more than the typical 12 to 14* BTDC.

 

You could POSSIBLY cheat it too. If you pull the front cover and use an adjustable timing set, you could advance the cam like 4 degrees. That COULD help with vacuum by closing the intake valve a little sooner.

 

What I find wild is that it is "technically" smaller than the Melling factory replacement for the 351w crown vic cam. It is on a narrower 112 LSA vs the 115 of the Melling. But there is a ton more intake duration on the "factory replacement ", at 283 degrees vs the 270 he has.


Melling factory replacement for FI 351w crown vic.

 

Just out of fun I put the melling cam in engine dyno, the difference in where the power curves are is interesting.

Edelbrock #2182



Melling SYB-35

 

a narrow lsa brings power down in the rpm range but idle suffers. That's why a good portion on factory cams are 113 and up. There are obviously outlying examples, but the majority of factory cams are in the one hundred and teens area.
You notice that the Edelbrock cam has power come on quick and then falls off, but the factory replacement melling makes power over a broader area. I have never been a fan of tight LSA cams outside of dedicated racing. And even then, i try to avoid it if possible. Tight LSA cams were designed to give a bit of streetability to a lumpy sounding cam. You just give it less overall lobe duration and tighten the LSA to get the potato-potato-potato sounding idle, that doesn't stall with a tight converter. But, doesn't pull up top either.
Heck, even the vaunted GM "offroad cam" sold in the 70s and 80s that made power out to 7500 was like 114 or 115 lsa. But, it needed 4.56 gears and a manual in a Vette or it was a dog till you got it revved to 4000.
Sizing cams can be tricky for street applications, efi even more so. Basically, find the cam you WANT and go 2 or 3 sizes smaller.