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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Slade88

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Some more updates, I had no car to get to work today so I had to drive it. This was the first time I drove it with the exhaust leaks fixed and my new map sensor and new 02 sensor, it drove a lot better and a lot smoother, no more backfiring, the engine still shakes a good bit at idle, but the whole truck doesn’t shake when driving unless I hit 1100-1200 rpm then the gas pedal starts to vibrate a good bit, the whole truck wants to shake when I’m stopped at a light with my foot on the brake and I let off the break a bit, or when I’m reversing with my foot on the brake lightly, it wants to shake then.

It still idled very rough, it was idling at 500 and got lower and stalled out at a light!! Then I started it up and everything was fine again

The truck still feels slower then it used to be

I don’t feel confident enough in my valve lash ability to do it by myself, so I’m not going to tackle that until I have someone to help.

I do not plan on driving the truck anymore until I get this sorted. It’s a shame these new sensors didn’t fix my issue
 

383_Stroker

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How'd it go?

Look your new plugs over really well, it's very easy to crack the porcelain installing a plug if you pull at all sideways on the socket.
 
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thatclappedsilverado

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These sbc trucks are pretty simple. if you have the cam . to . then the cam timing is fine. check the lash on the rockers and make sure its correct. everyone has their own way of doing it. i just shake the rocker and go till it doesnt have much play and a 1/4 turn. if thats fine. make sure the intake was tq properly. as well as the tbi. and make sure you have the plug wires on correctly. cause for as many engines. as i have built and sbc i have worked on ive made plenty of mistakes. haveing 1-2 plug wires on the wrong spot on the cap can be an issue with back firing. all in all it probably needs some more timing put into it. 8* isnt alot for that cam and i could be wrong but when i had the tbi heads on my truck with the comp 270h my initial timing was 12* and it ran and idled fine. there isnt alot to mess up on these engines. and your new dont beat yourself up over it the only real way to learn is from your mistakes. just double check your work. you could have a vacum hose not hooked up or one is leaking. these truacks are getting up to age. a few more years and mine will be 30. Hope you get it figured out. if you cant, bring it up to pa and ill help you work on it.
 

Schurkey

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if you have the cam . to . then the cam timing is fine.
There's no way to know that.

Mistakes happen when grinding the cam, when marking the timing set, etc. Don't get me started on the number of folks who've shot themselves in the foot with the multi-keyway timing sets.

The O-N-L-Y way to know for sure is to install the degree wheel and dial indicator.
 

Slade88

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Hello everyone, this will be my final update for this project!

I re adjusted my valves with a video from a channel called uncle Tony’s garage

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Linked here^

I also made sure all my plug wires were in order

It ran like a champ. It’s idling way high at 1500 rpm in park (don’t worry I’m fixing tomorrow). What should my target idle be in park on the road etc? I understand I need to adjust the idle screw with the iac in the home position and unplugged?

The engine shakes no more! No more smoke no more shaking gas pedal, all my wacky problems are gone, and my truck is faster then ever as well. Gas mileage also appears to have returned to normal

It doesn’t seem to want to stall either

The idle is way too high and my idle screw cap has already been drilled as I’ve fiddled with this before.

I would like to thank you all once again, I have read every single reply to this thread and done my best to follow everyone’s instructions. If not for this forum I’d be dead in the water

The truck also lightly backfires when accelerating really hard but I can live with it. I figure the computer is still going to need to adjust to the new hardware, I think my timings a little off as well, but these are not the most urgent issues to me.

Thank you!! Runs better then it ever has before
 

L31MaxExpress

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I would look at fuel pressure and timing. The best running of these engines had 13-14 psi fuel pressure stock and I have seen as little as 9.5 psi also stock. I have also found these engines generally like another 6-8° advance over the baseline of Zero or TDC. Most of them have less than 20° total advance at WOT, the heads like about 26-28°.

As for setting idle, jump a to b in the aldl plug, turn the key to run, wait 30 seconds and then disconnect the IAC connector. Start the engine and set it for about 550-600 rpm with the idle rate screw. Shut the engine off, plug the IAC back in and then pull the negative battery cable for 30 seconds, remove the ALDL jumper.
 
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