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abysmal cold starts after V cam install

HELLOW

Member
Joined
Jan 16, 2022
1992 240 +T, 440cc injectors, LH 2.4, chipped.

Swapped out the T cam for a V cam and now my cold starts are horrible. The engine chugs hard for the first 30 seconds it runs, idles super low, sometimes stalls out by itself. After it runs for 30 seconds or so it clears up and runs excellent, I am liking the powerband from the V cam.

Is the V cam just destined to have poor cold starts or can this be fixed? Two things I suspect could be causing this: I didn't check the valve shim clearances and the chips are made for the T cam. Will addressing these help the cold starts or should I just switch back to the T?

Timing was re checked, new distributor+ rotor, new plugs bpr7es gapped to .028.
 
You absolutely must check the valve clearance when changing the cam. My V was fine on cold starts. If you absolutely know that the CTS is reading right, that the maf is good, there are no vacuum leaks, and your injectors flow and scale how the chip is tuned for, then it should be good. Someone on the TB discord had rough cold starts that was solved with going to B230FT injectors and the resistor packs instead of the 850 orange top injectors, even though both flow the same at full duty, it seems like they didn't flow the same at very short injector rates.

Considering it's idling low, I'd suspect there's something there that's wrong with the TPS and IAC. Basically there's an issue with the mixture and combustion of your engine that is evident when the ECU is not looking for feedback from the o2. The ECU can't really learn in open loop.
 
Is it a recent swap or has LH had time to adapt to the new cam? My B230FD idled like crap just after i swapped from M to V, but got much better with time.
It's fairly recent, 3 weeks ago, daily driving it. It was improving slightly over time but it hasn't gotten any better recently.
 
You absolutely must check the valve clearance when changing the cam. My V was fine on cold starts. If you absolutely know that the CTS is reading right, that the maf is good, there are no vacuum leaks, and your injectors flow and scale how the chip is tuned for, then it should be good. Someone on the TB discord had rough cold starts that was solved with going to B230FT injectors and the resistor packs instead of the 850 orange top injectors, even though both flow the same at full duty, it seems like they didn't flow the same at very short injector rates.

Considering it's idling low, I'd suspect there's something there that's wrong with the TPS and IAC. Basically there's an issue with the mixture and combustion of your engine that is evident when the ECU is not looking for feedback from the o2. The ECU can't really learn in open loop.
I'll have to check the valve clearances that seems like the most likely culprit. It idles low in the first 30 seconds if you try to rev it up it chugs and barely runs. Then after it clears it has a normal idle speed. Chips are scaled, everything was perfect with the T cam.
 
V Cam actually sounded like a cam on cold starts for about 2-3 days until LH figured out what was goin on :LOL:, then it was perfectly fine. Check for vac leaks and valve clearance.

I later switched to "modern" injectors and noticed a smoother idle and slight bump in mpg, but it ran fine on the stock injectors for 2 years prior.
 
Hello,

I also installed a V Cam. I checked the valve clearance. everything fine. My cold start is also rough. But the engine doesn't stop. I think you have a problem, which is now made worse by the V Cam. In my experience, the valve clearance still fits when replacing original camshafts. Have you checked the compression?
 
It can be close on factory cam swaps, but it can be different, and it is always good to make it correct.
Tight lash will affect idle.
 
Tight lash will affect idle.
I didn't see anyone talk about why the cam change or tight valve lash will have such an effect. The reason is the change in manifold vacuum.

A longer duration cam will reduce the manifold vacuum you used to have with the stock cam. That makes the idle less efficient and cold idle can suffer a lot.

A tight valve lash will maximize the duration of the cam, so running with slightly looser lash will reduce duration and therefore increase vacuum. It can be enough to make cold idles more tolerable.
Dave
 
The lash will affect off the seat duration, but I don't think it'll affect duration @ 1mm enough to make a difference. I tried my V with .015" and .018" lash and it made no perceivable difference. I have zero cold starting issues or running irregularities with the A in my car now with stock LH, and the A has more off the seat overlap than the V. I strongly believe it's not the cam or the nature of LH.
 
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