e7engineer

88 with a 3.1 ( had it in it when the car was purchased ). The car misses badly, have a lot of black smoke coming from exhaust. Installed Vacuum gauge due to fuel regrlator operates off of engine vacuum. Gauge starts at 5" H2O, after about 30 seconds the vacuum increases to 20 to 22" H2O, then drops down again. Checked all vacuum lines and EGR Valve, Replaced PCV valve and hose, Replaced intake and plennum gaskets and spark plugs.
I was told by several people to that the timing chain may have streached, There is slack in the chain, how much is too much slack?
Any ideas would be helpfull........

Impreza WRX

The timing chain would affect the cam timing, but IIRC there should be a tensioner that adjusts for slack in the chain. If she's pouring black smoke, my guess is you're running richer than Bill Gates. How old are the vaccum hoses? If things are old rubber, they should be coming apart right about 5 years ago.

e7engineer

As stated earlier, Hoses are good, replaced the PVC hose. Don't know what a IIRC is, but the timing chain has no visable tensioners, just guides.

Impreza WRX

IIRC is shorthand for "If I Recall Correctly". In any case, if the cam was altering the timing, you would notice as the valves would be bent, unless the '88 has a non-interference engine. In either case, if you think the timing chain is too old, then change it. Just make sure to line up Top Dead Center correctly on both cam and crank. Once that is right, see if that fixes the missing problem. Is this engine EFI or carburated?

e7engineer

When I bought the car, someone replaced the 2.8 with a 3.1 throttle body