firebird904

I've posted this a few times in the v6 section with little response so I figured I would try here too. I have an 88 camaro with a v6 and for the most part it runs somewhat decent but here's some of the issues I've been having. I've been getting poor gas mileage, idle jumps around from 900rpm to 2000rpm, and I occasionally get a small backfire through the intake when taking off from a stop. It does not do this all the time only when it feels like it but it is getting a little more frequent although the gas mileage has been the same.

Things I've replaced,

plugs
wires
ICM
Pick up coil
ignition coil
cap/rotor
GM MAF
CTS
IAC
Air temp sensor
All vacuum lines
Fuel filter
Fuel Injectors


The only sensors I haven't replaced are the o2 sensor and the TPS. I checked the TPS with a digital multi meter and it's in good working order and I'm not sure about the o2 sensor. I know it's not original because it was replaced about 15 years ago by my father and the car had maybe 3000 miles put on it after that before it was parked but I'm not getting any codes at all ( except for code 12 ). I'm not really sure what else to do. Should I replace the o2? Any help would be extremely appreciated.

rgarcia63

Using the set initial timing procedure. You can check for timing stability, since the ECM timing control is disabled when setting the timing, the timing mark when seen with the timing light should stay steady at whatever idle speed you hold it at, ramp the rpm slowly from idle to 2000 rpm if the timing mark jumps around, the distributor needs to be replaced, or determine the cause.
You can also check for timing chain stretch by first turning the crank clockwise one full revolution just to take up the slack, align the mark with the zero on the timing tab. Remove the distributor cap so you can see the rotor, turn the crank-counter clockwise until you see the rotor begin to move. The distance the timing mark has moved is the amount the timing chain has stretched.
With a balancer diameter of 8 inches, an 8th inch stretch in the chain amounts to approx. 1.9 degrees in timing.
I would also do a cylinder leak down test to see if the valves are sealing properly.

Maverick H1L

iTrader: (8)

Have you replaced any top end gaskets? The valve cover gaskets have a tendency to dry out and cause a nice vacuum leak as well as an oil leak. PCV valve, tubing and grommets as well. I second the timing check... As well as a manifold vacuum test (at the back of the intake on the opposite side of where the brake booster hose connects). The vacuum may have dropped slightly with the new cam, but if it's ridiculously low, you have other issues.

firebird904

I will check the timing stability possibly today (if this darn storm calms down) and see what happens. The thing is that back when the engine was stock it did the same thing but one day it just stopped and I didn't have any more trouble till I took it on a 50 mile drive. I did a compression test and everything was within spec ( new rings ). I lapped the valves myself before I put them back in and the valves still looked good since the heads only had relatively low miles on them. All of the gaskets in the engine are brand new fel-pro gaskets. The intake backfire really is just a small pop when taking off sometimes but I can get on it at any speed after that and it gets up and go's just fine. Thanks for the help guy's I'll do that test and reply with results.

Maverick H1L

iTrader: (8)

Don't forget the vacuum test and make sure your valve covers are tight... And don't forget to check the ends of the idle air bypass pipe at the throttle body and intake manifold.

firebird904

I checked timing stability, that checked out good. Went picked up an o2 sensor and put it on and the idle leveled out and doesn't hunt now. I took it on a 20 mile drive and noticed a slight improvement in acceleration hopefully gas mileage will increase . I still however, have the small intake backfire but it only did it once today. I'm going to get a vacuum gauge sometime this week and will see how it goes.