I have a 1989 Camaro RS Conv with a 350 TBI (didn't come with the car) and recently its beginning to run really bad. I've replaced Fuel Filter, Spark plug wires (1 of them was burned a little), both fuel injectors, fuel pressure regulator, MAP sensor, cleaned out throttle body, used some top engine cleaner, set timing to where I believe it should be (was a little off before), replaced pcv valve, tons of other things and for some reason still running rough. When im sitting at a light it surges and sometimes cuts off and when it itles down to around 900-1,000 rpms I feel this strange vibration. Another thing is when I accelerate, just before it goes to shift the engine seems to bog out or hold back, which is something it didn't used to do. Also, I've checked the fuel pressure and it stays at 13 psi which is what its supposed to be at when its running but when I turn the ignition off it goes down to about 2-5 psi, then when I turn the ignition on it goes back up to 13 psi but immediately drops down to 2-5 psi until I start it, then it stays at 13 psi. Thats about all I can think of for now.. Any help would be greatly appreciated.. and sorry for the long post.

 

Check your ignition module. I had a similar problem on my '89 305 TBI. It turned out to be a bad module and the distributor was worn out at about 150k miles. I put a new aftermarket distributor in and it came with a new module. No problems since.

 

Its normal for your fuel pump to do that. TBI fuel pumps do not hold much residual pressure. Your pressures sound good.

The TBI engines are very basic and are usually very easy to diagnose. Check to make sure you have absolutely NO vacuum leaks. TBI engines like to suck in the TBI base gasket. Take some carb cleaner and spray all around the TBI base, intake manifold, and vacuum lines. You can also try blocking off the EGR valve, if its still there. The springs inside these diaphram type valves corrode or get weak and can cause pre-mature opening.
Could also be a weak coil. (I'm just throwing out random fixes from previous experiences).

 

Well, I fixed 2 problems.. but 1 of my problems is now worse.. I took the throttle body apart and found a bunch of old gasket material that had fallen down into the fuel inlet tunnels that go down into the fuel injectors, so I cleaned out the whole thing, and that really improved things, then I adjusted the timing and its running great.. except 1 problem.. While im sitting at a light or something the car kind of jerks back and forth when I take my foot off the gas, and it acts like its going to die but it doesn't any more. Also have a very bad vibration while sitting at lights. Im kind of new to messing with the timing so it is entirely possible its off. This is how I've set it, I unplug the connector the book says to unplug, brown connector? on the passenger side, right near the blower for the a/c I believe is where it is, I unplug that, then I set the timing, 1st time I set it 6 degrees before top dead center, then this last time I think its set for 12 degrees, now it runs great except for at idle. Thanks for replying by the way.

 

12 seems a little high, but I dont know your setup. Are you getting any pinging from the engine under WOT? With my stock 305 tbi I could only get about 8* advance, and with the heads/cam I can pull about 10*. If I go up to 12* it does what you say, at idle it'll down down to about 300 rpm, then hop back up to 600. If I pull the timing down to 8-10 it idles great though. You're setting the timing right though Are you running 92/93 octane with that high of timing?

 

Isn't it 6 deg for most any 3rd gen?

 

Of course
All I run in my cars are 93 octane. Im not really getting any pinging or anything but Im getting this ticking noise (but I''ve had that no matter what I set the timing to, not sure what it is, think I have a leak in exhaust manifold(s) but that will go away when I put the headers on..).

Its more or less completely stock, no real modifications except the new exhaust system, I think its a 80 series? Flowmaster exhaust, bullett high performance cat (seems to basically just be a shell).

I'll try turning the timing down from 12 to between 8-10 and give that a try.. I skipped the minor changes and jumped it up to 12, just to see what would happend.. I get awesome acceleration but shi**y idle.

 

I tried that but I had slight detonation at idle and also at WOT it would bog out to nothing and then shift.

 

If you can get your hands on a lap top, definitely hook WinALDL up to your car. If the timing doesnt help it, that should give you some idication as to where to go. I dont see why you'd get detonation with 6* advance though. Is it backfiring at all?

I should also add it'd be great to check your knock counts with winaldl. If they didnt change the knock sensor to a 350 one when they did the engine, the 305 one likes to register a lot of false knock from what Ive read. Could be retarding your timing to the point where the car just cant idle.

 

Hmm, ok I'll give it a try, I have two laptops I can use but I don't think I have a cable that would work, may have to buy one. I set the timing to 8 degrees before tdc and its even worse than at 12.. Seems to get better the higher I go, maybe I should try it as high as it will go and see what happends.

 

Ah, you know I'd bet your distributor is off a tooth. Check that, too.

 

Off a tooth? Oh god.. you mean I've got to take the distributor back out again? grr..

Whats the best process? Should I set the timing mark to top dead ctr and then remove it? After its removed how exactly do I rotate it to get it exactly right? (that is if thats what needs to be done.)

 

That sounds to me an awful lot like a 305 sensor picking up false knock in the 350 and retarding the hell out of the timing. I'd start with a new 350 knock sensor and set the base timing at 8* and see what you get.

If you're checking your timing with a timing light then having the distributor a tooth off won't change the actual timing, only how far either way you can rotate the distributor to adjust it. If you can adjust it between 0* and 20* BTDC then you're on the right tooth.

 

Ok, I'll go pickup a new knock sensor today.. Thanks for the help all, will see if that fixes it.

 

Oh yah, another question, since I have a 350 instead of a 305 with a TBI, most of the parts stores list certain engine types, like 5.7L FI (TPI) and they have a 5.0L TBI listed.. Since mine is a 350 TBI and not TPI, should I use parts for a 5.0L as listed or use the parts listed for the 350? For fuel injection replacement parts I've had to tell them to look up a GMC Truck with a 5.7L TBI (wasn't my choice really, it was how the car came) and I've yet to decide whether I should spend all the money to put a TPI setup on it or just toss a carb on it.