So two days ago, i was driving around like a normal guy, it was on Halloween, and I went to my house and hung out there with the parents. Then when I left i started driving and then a few minutes later the car felt like it lost power, and shakes like I have Michael J Fox for an engine. So I checked some plugs and they were fine, all the cylinders are firing ( primary water pouring test when hot) and all distb wires are connected and so are all the vacuum stuff. Only thing that isnt connected is the air pump stuff, and along with it starting to shudder upon throttle the air pump started pumping as well at the same time the shuddering happened. It sounds like I'm driving around with a knock, but if you plug up the hole on the back the sound is gone... There's also a missing kinda sound coming from the tailpipes... Along with checking the plugs, wires, vacuum, distributor, i replaced the esc module, the flat pancake connector on the driver side part of the firewall and its still shuddering/studdering. What Could I be missing?

 

Huh? What is a "primary water pouring test"?

If you want to know if the cylinders are running, I suggest a cylinder-balance test, where you kill the spark to one cylinder at a time while watching a vacuum gauge connected to manifold vacuum.

So the air pump function and the shuddering happen simultaneously? Any chance the air pump is pushing air "upstream" which tells the O2 sensor the exhaust is very lean? Perhaps a defective diverter valve, or perhaps the computer is falling out of closed-loop, and pushing air upstream to help heat the catalytic converter?

[What's up with the automated link to eBay when I type in " catalytic converter "? That link is NOT my doing.]


WHAT hole?

If this were in my garage, I'd be doing a cylinder balance test, perhaps a compression test, perhaps a leakdown test, and I'd connect a scan tool to look at the data stream. Anything else is stumbling around in the dark, hoping for "good luck".

 

Ran a scan tool and it said there was nothing wrong. The water test is pouring water on the header primaries and if it bubbles off like boiling water then the cylinder is firing. Pullef all the plugs and only one is a little black. As for the hole. Its on the back of the air pump on the driver side. The smog pump?. I never had the whole thing completely off when i did the headers and it didnt do anything till now and when I turned it on the "knocking" sound was like pushing air out. Cover up the hole. sound went away. But thats all so far. I may not bothe r with the 305 as I have found vortec 350 with 100k on for 250 I may swap it.

 

Scan tool, or crappy code-reader? You're looking for the data stream more than for codes.

 

both injectors spraying evenly? Could try a set of new plugs if nothing else found wrong-sometimes a spark plug can look good,but have a cracked insulator or other fault that only acts up at certain times.

 

I could be weak fuel pressure, tbi will run on ridiculously low fuel pressure. Stock spec is 9-13, I've seen em run on 5psi (just not very well).

 

Well spray pattern was equal looking, yes it was a cheap scan tool my service engine light turns on after warm up cycle, but there are no codes, some days it goes away, some times it doesn't. All the plugs were fine accept for cylinder #4 plug. It was running rich, so i wonder if it fouled out and caused it to detonate sometimes, and to sometime not detonate. But, i came across a vortec 350 deal so Ill be doing that swap within the next week.
** pulled the plugs, all were good except number 4, and replaced it fixed the shuttering Thanks for all the help! Sometime times its only one little thing that can make or break what is goin on haha