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Vacuum on 2.8L in 86XJ Cherokee Bill Huges -Help please!

STILL have problems getting sufficient vacuum on 2,8L engine. Suggestions greatly appreciated.

Problem is engine does not develop sufficient vacuum to run emission controls nor sufficient vacuum to run dist. advance etc. correctly. Carb (vari-jet Rochester) running too rich due to low vacuum; two carbs applied and both act exactly same (to eliminate/isolate carb problem). BOTH carbs worked fine/perfect on other engine!

Compression is at top of specs. All cylinders equal in pressure. I rebuilt this engine about 3 months ago.

Mechanical timing is correct, alignment/position of cam/crank at index re: timing chain, etc. NOT a 'jumped' timing chain tooth, etc. Runs retarded after set up w/ #1 piston @ tdc and matched to vibration damper. Max. idle/max vac. occurs at ~ 20°TDC. No visible leaks at intake manifold with either ether or propane at manifold-block joints/gaskets. Engine will significantly *increase* rpm when ANY vacuum hose is pulled from intake manifold, so I'm pretty sure I dont have an intake manifold leak. Otherwise runs too too rich.

Only thing not tested is distributor control module and spark pick-up assembly in distributor.

ANY suggestions would be GREATLY appreciated. (damn engine is now heavily fouled with carbon)

Reply to
RichH
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Reply to
L.W.(ßill)

Ha ha ha .... I know how to downshift so small engines are my forte and fuel economy on long haul is my goal. On a well tuned 2.8L I can get

22-23 mpg and normal highway speeds with my antique Cherokee.

Dead steady vacuum gauge but at 10 inches hg. vac. THATS the problem cant get 15! No emissions control below 15!

Could the distributor module be faulty and firing the coil early .... how does one test the dist. module??? .... other than swapping modules?

Cross cylinder blown gaskets - no physical evidence. Buy sicne you posted it Ill check by doing a volume/pressure leak down test.

I'm running out of ideas and am becoming quite 'frazzled'.

Thanks

L.W.(ßill) Hughes III wrote:

Reply to
RichH

Reply to
L.W.(ßill)

Timing chain.....

Maybe #1 isn't on the right distributor cap post or does it matter in that engine? Could be thinking of a different one.

I am not sure on that engine, but some also will run with the distributor 180 off. They just run poorly.

Are you sure that #1 is at TDC on the compression stroke when the rotor is tagging that post in the cap?

I stick my finger in the spark plug hole and use a wrench on the crank bolt to turn the engine as it comes to 0 on the timing mark.

It only hits compression every two turns of the timing mark.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

RichH wrote:

Reply to
Mike Romain

Reply to
RichH

Constant low vacuum is quite often caused by a blocked exhaust system. Could be a clogged converter or possibly the muffler has collapsed internally.

Chris

Reply to
c

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