1989 318 Running rough.

[Huttemannc]

Hey, I have an 89 with a 318 that has about 53k original. Never rebuilt. About a month ago it started running super rough. It idles fine, but under load it just has no power and bucks and shakes real bad. I was thinking spark, so I changed the plug wires, plugs, cap, rotor. Solved nothing. I was thinking fuel delivery, swapped out the fuel filter, fuel pump, fuel lines. Solved nothing. Both injectors on the tbi seem to be pushing the same volume, should I swap them? I know i need to replace the temp sensor, as it no longer reads on the dash, that wouldn't be the issue would it? it went out months prior to the engine running rough. Throttle position sensor? Vacuum leak? Ive looked for leaks and cant find any, it seems to idle at a constant RPM. Jump time? That is something i really havent looked at, i dont have access to a timing light, but can get one if need. What is the recomended advance on that engine? What have you all found to be a time setting that is good for a daily driver? i really am at a loss here. Is there any benefit to puling the TBI and dropping a carb on it? what all is entailed in such a task? any carb suggestions if that is the route to go? Dash codes are normal with nothing hinting at the engine, just a battery negative disconnect (?) and a A/C relay fault. Any help or ideas would be super helpful. Thanks.

 

[El Huapo]

It looks like you have done what I too would have done already. But one thing I learned from my dad was to check the mechanicals too. By that, I mean to do a compression check and while the plugs are out, roll the engine around to #1 cylinder at TDC (I put a ty-rap with a second one threaded into it to make a "T" so it can't go down inside) and look at the timing marks. Hopefully it will be at the right place. Other folks will demand a "Leak-down" test too, but I never did that.
Note: the #1 piston will be at the top of its travel twice in a cycle, so don't let that fool you, keep rolling it.
I had a similar truck that had the trans get a little goofy under hard throttle that shifted up and immediately back one time, over-revving and it bent one valve just a little tiny bit, but it subsequently acted similar to your description. A valve job solved that, thankfully there was no discernable damage to the piston.
Farther in the past, I had a '68 327 El Camino with a "Flat cam" which only missed under load. It's other noticeable characteristic was a "Popping sound" down in the manifold that you could hear with the air cleaner off. A mechanical friend told me to look for that and yep, it was there and the cam had one lobe that was completely round. In those days, it was only a Saturday morning job to replace the cam and lifters, engines were clean then. Also, with the valve cover off, you could see that one valve rocker just didn't move like the others.
Best wishes on your hunt.

 

[gogereaver]

Same problem I'm getting code 36 on the computer.