Engine and car shakes bad/ misfires on the road after cam swap (CL-12-249-4) 1988 Chevy C1500 aTBI 350

Slade88

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Hey everyone, I’ve made a couple posts here about my cam swap I did on my truck. Well I finally got it idling 950 rpm in park with a rough idle, 550 in gear when the truck is hardly in motion and 1000 when the truck is moving very fast down the road with my foot off the gas.

Timing is set at about 8 degrees very close to 0 degrees TDC.

It’s running a little more hot then usual but it keeps a consistent temperature.

My gas pedal feels more stiff then usual and vibrates when I press on the gas, the whole car vibrates past 1000 rpms and backfires slightly at 3000 rpm, I have a little less power then usual but my power band has definitely moved up in the rpm’s

I have 2 pretty bad exhaust leaks from where the headers connect to the exhaust pipes which I assume is causing some of my issues

When I rev the engine is park at high rpm it blows black smoke which looks like unburnt fuel

My engine also shakes a lot at idle when I pop the hood, a lot more then usual

I have a feeling it’s running rich and not burning all the fuel because my gas mileage has gotten significantly worse as well.

Is it safe to drive before I fix all this? Like it won’t damage anything driving it?

I don’t expect my truck to run as smooth as it did with the stock cam but this is kinda ridiculous how bad it seems to run now.

I have my check engine light on and plan to pull the codes in a couple hours

Could this just be my computer acting up with the new hardware? It’s not that big of a cam

Thanks!
 

RichLo

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Have you done anything with the TBI tuning to give you a better baseline? Are the o2 sensors new? Are you confident your valve lash is set correctly?
 

Schurkey

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I finally got it idling 950 rpm in park with a rough idle, 550 in gear when the truck is hardly in motion and 1000 when the truck is moving very fast down the road with my foot off the gas.
That's terrible.

Timing is set at about 8 degrees very close to 0 degrees TDC.
8 degrees is 8 degrees away from TDC. That's not "close".

My gas pedal feels more stiff then usual and vibrates when I press on the gas, the whole car vibrates past 1000 rpms and backfires slightly at 3000 rpm, I have a little less power then usual but my power band has definitely moved up in the rpm’s
Was the cam degreed when installed, or did you rely on "Dot-to-dot" for cam timing?

What is the cranking compression pressures of all eight?

Are all the plug wires installed correctly? Have you checked the spark plug condition? Cap, rotor, plug wires in usable condition?

What is the fuel pressure?

EGR stuck open?

Lifter preload too tight as has already been hinted at.

I have 2 pretty bad exhaust leaks from where the headers connect to the exhaust pipes which I assume is causing some of my issues
Maybe. I think there's way more wrong than that, though.

When I rev the engine is park at high rpm it blows black smoke which looks like unburnt fuel

My engine also shakes a lot at idle when I pop the hood, a lot more then usual

I have a feeling it’s running rich and not burning all the fuel because my gas mileage has gotten significantly worse as well.

Is it safe to drive before I fix all this? Like it won’t damage anything driving it?
You're washing the oil off the cylinders, causing cylinder wall wear. You may have already overheated the catalytic converter.

NO. FIX THIS before driving around.

I have my check engine light on and plan to pull the codes in a couple hours
Don't just "pull codes". Look at the data stream--verify EVERY sensor; especially coolant temp, MAP, TPS.

Could this just be my computer acting up with the new hardware? It’s not that big of a cam

Thanks!
I think you've got more going on than just a computer reacting to a non-stock but mild cam.
 

Slade88

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Have you done anything with the TBI tuning to give you a better baseline? Are the o2 sensors new? Are you confident your valve lash is set correctly?
I’ve adjusted the idle screw but that about it, o2 sensor was replaced last year
 

Slade88

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That's terrible.


8 degrees is 8 degrees away from TDC. That's not "close".


Was the cam degreed when installed, or did you rely on "Dot-to-dot" for cam timing?

What is the cranking compression pressures of all eight?

Are all the plug wires installed correctly? Have you checked the spark plug condition? Cap, rotor, plug wires in usable condition?

What is the fuel pressure?

EGR stuck open?

Lifter preload too tight as has already been hinted at.


Maybe. I think there's way more wrong than that, though.


You're washing the oil off the cylinders, causing cylinder wall wear. You may have already overheated the catalytic converter.

NO. FIX THIS before driving around.


Don't just "pull codes". Look at the data stream--verify EVERY sensor; especially coolant temp, MAP, TPS.


I think you've got more going on than just a computer reacting to a non-stock but mild cam.
It has new spark plugs and all new plug wires, the distributor is in pretty good condition.

That’s about how my truck idled before the cam swap and for years I never had a problem with anything

I installed it dot to dot like every video online said

Right now I don’t have a compression tester

How do I test the fuel pressure?

Not sure if egr is stuck open or not

They might be, I tightened them down until I felt resistance spinning them as I hand cranked the engine then when they all had resistance I gave them a quarter turn, this is the first time I’ve ever set lifter pre load

It runs a little more hot then usual and it has 2 new coolant sensors

Luckily I don’t have a catalytic converter

That sounds very bad f!ck.

I don’t have anything to test a data stream with and don’t have the money or the know how to operate one

Really regret doing this, all the videos and forum threads made doing a cam swap sound like changing a battery. Wish I never did this. I’m thinking of taking it to a shop so they can run their fancy computer on it and tell me WTF is going on. Really hope I have not permanently damaged my engine from my own foolishness. Thank you for the advice, I don’t really know where to start anymore, the truck ran absolutely perfect before the cam swap and all the sensors performed correctly, now it’s like nothing works, I don’t even care if my car shakes at this point I just want it to be able to take me from point A to point B without tearing itself apart. Other then that IDGAF at this point in time, used to care about speed but it seems that’s out the window at this point
 

RichLo

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I’m thinking of taking it to a shop so they can run their fancy computer on it and tell me WTF is going on.

Probably your best option right now but call ahead to make sure they will actually work on it. Some shops will flat out deny to work on a vehicle that an owner has modified and now isnt running right. Or they will only give you a quote for bringing it back to stock.
 

Schurkey

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I tightened them down until I felt resistance spinning them as I hand cranked the engine then when they all had resistance I gave them a quarter turn, this is the first time I’ve ever set lifter pre load
That's a red flag.

"Spinning" pushrods is fine...IF you've done it before so you have some idea of how much drag to feel for, (Hint: Not very damn much) and if you're certain the lifter is on the base circle.

I've seen guys spin pushrods until the lifter is totally collapsed, and then give 'em another half-turn, making absolutely sure that the valves can't close properly. If the engine runs at all, it runs shiitty, rough, shakes like it's having an org_asm. The faster the engine turns, the better it gets--but it's never right.

When I set lifter preload, I either lift the pushrod to check for up 'n' down clearance, or move the rocker up 'n' down.

Loosen 'em all, so the pushrods all have vertical play. Tighten 'em all until the pushrods have NO vertical play. Turn the crank exactly one full turn--360 degrees. SOME of the pushrods will have play. Tighten only those, until there's no play. Then tighten all of them "your choice" of preload. 1/2 turn is common. GM used to recommend 1 full turn. Some lifters have restricted travel, and may need less preload.
 
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Slade88

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That's a red flag.

"Spinning" pushrods is fine...IF you've done it before so you have some idea of how much drag to feel for, (Hint: Not very damn much) and if you're certain the lifter is on the base circle.

I've seen guys spin pushrods until the lifter is totally collapsed, and then give 'em another half-turn, making absolutely sure that the valves can't close properly. If the engine runs at all, it runs shiitty, rough, shakes like it's having an org_asm. The faster the engine turns, the better it gets--but it's never right.

When I set lifter preload, I either lift the pushrod to check for up 'n' down clearance, or move the rocker up 'n' down.

Loosen 'em all, so the pushrods all have vertical play. Tighten 'em all until the pushrods have NO vertical play. Turn the crank exactly one full turn--360 degrees. SOME of the pushrods will have play. Tighten only those, until there's no play. Then tighten all of them "your choice" of preload. 1/2 turn is common. GM used to recommend 1 full turn. Some lifters have restricted travel, and may need less preload.
I always have the mentality that a little too loose is better then a little too tight, all my rocker arms go all the way up and back down as well, just as they did with the original camshaft, they all look even, I didn’t have but a little bit of metal in the oil during the initial break in. I spun them until I felt the slightest resistance then I stopped, my cam manual said half a turn for the lifters I got with the kit, I have no ticking or popping sounds from the engine if that means anything. But knowing me I’m not surprised if I screwed this up too
 

Slade88

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I found a shop very close to home that will run one of those fancy obd1 computers on my truck for an hour for $140. Would it kill my engine to drive a mile down the road to the shop? If anything’s wrong I’ll pay them to fix it
 
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