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

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RichLo

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Tough situation and it sucks your first major upgrade had to go south.

This is definitely not the recommended way of tuning the computer after a cam swap but if you drive it an hour, dont be surprised if it starts running better. It wont get perfect since there was a problem before the cam swap and a shop still needs to run diagnostics but the computer might start learning the new cam as you drive. As long as there isnt a major mechanical problem like lifters collapsed from tightening too much, it should make it.

Also, if you haven't already, you might want to change the oil for some high-ZDDP cam break-in oil before the trip.

If your Ford friend can at the very least double check your valve adjustment before the trip, you can feel better about that at least.

We could list a dozen things to check but it sounds like your backed into a corner at this point.
 

Slade88

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Tough situation and it sucks your first major upgrade had to go south.

This is definitely not the recommended way of tuning the computer after a cam swap but if you drive it an hour, dont be surprised if it starts running better. It wont get perfect since there was a problem before the cam swap and a shop still needs to run diagnostics but the computer might start learning the new cam as you drive. As long as there isnt a major mechanical problem like lifters collapsed from tightening too much, it should make it.

Also, if you haven't already, you might want to change the oil for some high-ZDDP cam break-in oil before the trip.

If your Ford friend can at the very least double check your valve adjustment before the trip, you can feel better about that at least.

We could list a dozen things to check but it sounds like your backed into a corner at this point.
I’ve driven it about 40 miles city driving, with no noticeable change in my gauges or how the engine acts, just the same consistent problems I mentioned, wouldn’t internal engine damage manifest it’s self during this period? I’m genuinely thinking my two massive exhaust leaks could be causing the misfiring/bad gas mileage/backfiring/shaking problems. Before I half assed re installed the headers my engine ran smooth in the garage. When I first installed the cam the engine ran great but it was slow on the road because I hadn’t set the timing. Wouldn’t any internal engine damage occur during the 30 minute break in period? I’m going to fix the exhaust leaks tomorrow and see what happens.
 
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Make sure your timing is set correctly, not close, but to the factory specification which I believe is 0°. How much manifold vacuum is the engine pulling at idle in park? What timing set did you use when you put the camshaft in? Is it one of the aftermarket timing sets with multiple keyways that allow you to advance/retard the timing?

I suspect that your valves are improperly adjusted, or you could have ignition system problems i.e. wires, plugs, cap, and rotor. That camshaft is fairly mild and shouldn't cause that much trouble.

Try reading this for valve adjustment procedure:

Keep it simple, and adjust one cylinder at a time. I have adjusted the valves on hundreds of engines using this method and it works. I think you are over thinking this whole thing, and just need to start with the basics and figure this mess out.

Readjust your valves using the method in the link on the Pace Performance website, set your timing, and see how it runs.

I worked for GM dealerships for 15 years, including 11 years in our GM Performance Parts engine shop, so Chevy V8's have been my specialty. Good luck with your project.
 

thebigcar

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I just skimmed over the first page so I don't know if this was already done but FIRST thing I'd double check is spark plug wires going to the right cylinders. You may be off one on the distributor .... Then I'd (re)check valve lash. Normally lash not set correctly (all the way around) will give you firery backfires through the carb / TB or a lot of valve train clacking

To me, this is a dead giveaway:
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

and this

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

and this

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

Sounds like you got a cpl of dead cylinders or misfiring which is probably spark related considering the work you did

EDIT **** after proof reading it occurred to me you may have done the install so terribly (or didn't check your valve lift / timing vs piston clearance before ordering the cam) that you bent a valve or 2 or 3 or 4 in which case, expensive lesson learned.
 
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383_Stroker

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Aside from all your major issues. Exhaust leaks anywhere near the O2 sensors will likely cause them to read lean and cause the ecm to add additional fuel to compensate.
 

Crome_C1500

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U need a flashed chip ,ur running too rich, tbi are always gonna run ruch when u mod the truck, I have a 91 c1500 with edelbrock intake,headers, spacer on the tbi, msd and a compcam and had the same problem
 

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Slade88

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Ok everyone a couple updates, I appreciate all the help once again! I got the headers real tight to the exhaust pipes so the leaks should be gone (have not started the truck yet). I have ordered a new o2 sensor that I will install tomorrow, I replaced the map sensor as well. I’m trying to give the computer a fighting chance to fix the rich condition of the air/fuel ratio. The cam is very very mild so I doubt I bent valves due to the cam itself I also did do my cam timing correctly. Valve lash is probably set wrong, all of these problems I now have did not happen during or after cam break in. They happened after I messed with the headers the timing disconnected the battery probably wiping all the fuel maps and other critical data.

I’m doing everything I can before I get into valve lash because I’m dreading doing that by myself again (and of what I might find). I will get timing exactly on 0 degrees after everything else gets sorted with the first start after all the new sensors I’ve installed, the sensors are original and I’m guessing they over heated during the break in.

I’m also going to check to make sure those plug wires are on the right way, I feel like most of my problems are due to the engine running extremely rich. And when I pulled codes it told me I had a bad o2 sensor bad map sensor and possibly a bad EGR valve which I will replace as well when I have the money
 

Schurkey

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"Codes" do not tell you that you have a "bad O2 sensor" or a "bad MAP sensor".

"Codes" tell you that there's a problem somewhere in the sensor circuit. Could be the sensor...could be the wire harness. Could even be in the ECM itself. Could be unusual operating conditions caused by a fault somewhere else.

Stop replacing parts, do more diagnosis.

Disconnecting the battery does not "wipe critical data". It clears codes, and clears the ADAPTIONS to the fuel tables. Those adaptions are rebuilt as you drive. The base fuel tables--without adaptions--are close enough to make the vehicle run adequately enough to be safe to drive, as it rebuilds the adaption database.
 

351FUN

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Ideally I would like to fix it myself, I do have a mentor who knows just about everything about cars but isn’t familiar with chevys (ford guy).

I'm a Ford guy. It's all very similar. Chevy does some really stupid **** with this engine but it has the same parts as a Ford.

The distributor is original so is the cap and ignition coil.

Those are a prime suspect. Cap and rotor are day 1 replacement items for me on a new used vehicle, along with plugs and wires. The distributors on these engines start to really act up after 100k miles. Cap and rotor are cheap and easy to replace, even with Chevy making the engine backwards. You really need more testing and less shotgunning though tbh.
 

RichLo

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Valve lash is probably set wrong, all of these problems I now have did not happen during or after cam break in. They happened after I messed with the headers the timing disconnected the battery probably wiping all the fuel maps and other critical data.

I’m doing everything I can before I get into valve lash because I’m dreading doing that by myself again (and of what I might find).

Are you saying now that it ran absolutely perfectly after the cam swap and your problems happened only immediately after installing the headers? Diagnostics change if this is the case.

If not and you are still suspecting valve adjustment, DO NOT RUN IT until you re-adjust the valves!! Get yourself a hand start switch to rotate the engine and take your time and go 1-cylinder at a time with a battery charger hooked up. Its not that hard, just takes time.



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