Warm start stumble/bog after cmcv system disabled

[s197richie]

My car had been sitting a long time and rats made a real nest in the intake valley. There were too many rusted fasteners for me to deal with it so I farmed it out to a local guy who specializes in performance, restoration and repair of all gens. He suggested an unhook of the cmcv system while he was in there and since he has decades of experience I figured sure. So anyway he repaired the rat damage and the car runs great; it does set codes for runners since the cmcv is unhooked. But on warm or hot restarts it does stumble and bog horribly; it goes away after a couple accelerations but it's just kind of annoying and embarrassing. Maybe the ecu is trying to detect the cmcv and making an adjustment when it doesn't see it; idk. Anyone else experience this? TIA preesh

 

[Dino Dino Bambino]

A CMCV delete requires a retune to adjust for the altered airflow characteristics. Only then will you see the full performance benefit.

 

[StockishS197]

Just to be sure too, did you just unplug the CMCVs or install CMDPs?

If only the former, I would suggest installing CMDPs and getting a tune as Dino suggested.

 

[07 Boss]

What exactly did he do to unhook the charge motion plates? I mean if he just disconnected the electrical connector that would be worse than actually have them operating. Did he remove the butterflies or did he prop them open? Did you get a tune for them not operating?

 

[s197richie]

What exactly did he do to unhook the charge motion plates? I mean if he just disconnected the electrical connector that would be worse than actually have them operating. Did he remove the butterflies or did he prop them open? Did you get a tune for them not operating?

He told me there was mechanical linkage he could unhook so the mechanism would just lie flat. Prior to the repair the car ran great at higher rpm's but under say, 3500rpm if you floored it, it would stumble and slow down. In addition to the cmcv unhook he also changed the spark plugs, replaced a cracked coil, and ungunked any buildup he found (I've since installed a catch can). The car was only started once per week for a few years so I imagine there was a lot of blow-by accumulated by not actually taking it out, warming it up and winding it out. The car is still running the 93 octane Brenspeed OTS tune which only accommodates the C&L cold air intake modification. The understanding was the cmcv unhook wasn't going to improve performance but it was a bad design and better off disabled.

 

[07 Boss]

He told me there was mechanical linkage he could unhook so the mechanism would just lie flat. Prior to the repair the car ran great at higher rpm's but under say, 3500rpm if you floored it, it would stumble and slow down. In addition to the cmcv unhook he also changed the spark plugs, replaced a cracked coil, and ungunked any buildup he found (I've since installed a catch can). The car was only started once per week for a few years so I imagine there was a lot of blow-by accumulated by not actually taking it out, warming it up and winding it out. The car is still running the 93 octane Brenspeed OTS tune which only accommodates the C&L cold air intake modification. The understanding was the cmcv unhook wasn't going to improve performance but it was a bad design and better off disabled.

Well that's your problem. If they are just lying there flat, in the closed position, you are choking the motor. If you have them propped open the car won't idle correctly. See, at idle or low rpm the plates are closed/flat with a small opening to let air through. This makes the air turbulent and supposed to help the air fuel mixture. When you step on the gas they will open and allow air to pass more freely. If you want to delete them you need to remove the butterflies, not just unhook the mechanism. Either hook them back up or delete them properly and get a tune. Your car won't run correctly as you have restricted the air flow. It won't have any power and like you have been experiencing, starting issues. The butterflies may be opening a bit after you rev it just because the airflow is forcing them to open and why it might run a little better after that. But either way you need to delete it properly or hook it back up.

Oh and don't go back to that mechanic anymore, he's an effin hack.

 

[StockishS197]

Pull the intake manifold and make your own CMDPs from your CMCVs. Plenty of write ups if you don’t want to buy the Steeda Billet CMDPs.

Then contact Brenspeed for an updated tune to update for the CMDPs and your car will run better.

 

[07 Boss]

Do you see those butterfly valves? If they are closed or lying flat, they are choking off the air flow. They linkage he unhooked is preventing these from opening. So either remove the butterflies and fill the holes or reinstall the mechanism so they work properly.

 

[JC SSP]

I did mine with high temp two-part epoxy rated for metal. No issue and cost me $10.00. I also did a little polishing… lol old hot rodders never die.

 

[Juice]

You can't delete those without making tune changes.
Long runner low rpm torque, short runner high rpm power.
You cannot change the laws of physics, delete and you will lose low end torque.

 

[Dino Dino Bambino]

delete and you will lose low end torque.

I can tell you from first hand experience that is 100% not true.
This isn't a variable runner length intake manifold with valves to switch from long narrow runners to short wide runners at a certain rpm. The CMCVs are only there to minimise cold start and idle emissions.

 

[s197richie]

Oh and don't go back to that mechanic anymore, he's an effin hack.

Well I wonder why he'd do that; his personal vehicles are a FBO Termi and Trinity GT500. I didn't specify any budget; he wrote up everything he recommended and found damaged and all I subtracted out were new fuel injectors since those I could just easily do myself down the road if issues persisted.

His experience with all gens is noteworthy and I didn't ask him to cut any corners or save me money.

TY

 

[StockishS197]

Well I wonder why he'd do that; his personal vehicles are a FBO Termi and Trinity GT500. I didn't specify any budget; he wrote up everything he recommended and found damaged and all I subtracted out were new fuel injectors since those I could just easily do myself down the road if issues persisted.

His experience with all gens is noteworthy and I didn't ask him to cut any corners or save me money.

TY

Probably because it will still technically run, just not well.

The intake manifold removal on these cars is really easy. And once that’s off, the CMCVs are held on with 4 bolts. Very straightforward to do, even with minimal tools/experience.

 

[s197richie]

What exactly did he do to unhook the charge motion plates? I mean if he just disconnected the electrical connector that would be worse than actually have them operating. Did he remove the butterflies or did he prop them open? Did you get a tune for them not operating?

I contacted him today since I was considering Brenspeed Detroit Rocker cams and either proper Steeda delete plates or a whole hog FRPP intake and asked him if I only did the cams and retune should I mention to them the cmcv system is currently disabled (they are propped wide open at the moment; before I wasn't sure about that detail). He did say the cam upgrade would require proper deletion of the cmcv but nothing about a need to retune it right now for the prop job. It runs strong but just stumbles a bit on warm/hot restarts for the first couple take-offs. Thoughts? TIA

 

[07 Boss]

I contacted him today since I was considering Brenspeed Detroit Rocker cams and either proper Steeda delete plates or a whole hog FRPP intake and asked him if I only did the cams and retune should I mention to them the cmcv system is currently disabled (they are propped wide open at the moment; before I wasn't sure about that detail). He did say the cam upgrade would require proper deletion of the cmcv but nothing about a need to retune it right now for the prop job. It runs strong but just stumbles a bit on warm/hot restarts for the first couple take-offs. Thoughts? TIA

Well if they are propped open it will still need a tune to get rid of your stumble. It does this because it is tuned for a different air flow at the lower rpms when the valves are either closed or slightly open.

 

[StockishS197]

I contacted him today since I was considering Brenspeed Detroit Rocker cams and either proper Steeda delete plates or a whole hog FRPP intake and asked him if I only did the cams and retune should I mention to them the cmcv system is currently disabled (they are propped wide open at the moment; before I wasn't sure about that detail). He did say the cam upgrade would require proper deletion of the cmcv but nothing about a need to retune it right now for the prop job. It runs strong but just stumbles a bit on warm/hot restarts for the first couple take-offs. Thoughts? TIA

Skip the FRPP mani and go with the Steeda Plates

I have had both. The FRPP will pull slightly harder up top (6500+ RPM) but be slightly softer in the low/mid range. With basic cams and bolt ons, you really won’t notice a difference.

The biggest reason I pulled off the FRPP mani and went back to stock IM + Steeda CMDPs was tuning around the EVAP purge system was a nightmare for idle quality with the FRPP. The EVAP design is poor and will cause idle fueling issue during purge that is essentially impossible to correct unless you disable or partially disable EVAP purge at idle. Instead of evenly distributing the purge (fuel vapor from gas tank) like the stock IM, it dumps it into the driver side port and causes uneven fueling during purge.