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off topic....rough running non gm van.


handmedownreatta

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my van went from running great to barely running in about thirty miles.its running really rough, sometimes backfires under acceleration,has a ticking noise.the oil on the dipstick isn't milky.its not running hot.oil pressures fine.i used a vacumn guage at idle and discovered the vacumn moving rapidly back and forth between 3 and 7 pounds.i don't think clogged cats because lots of flow out of the tailpipe.its a multi fi system.i ordered an adapter to hook to my scan tool but its not here yet.any ideas?

Edited by handmedownreatta (see edit history)
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It does sound like a vacuum leak with readings that low. It should be in inches of mercury if it is a vacuum gauge but that's only a detail. The rapid fluctuation generally points to a valve problem of some kind, sticking/bent valve or possibly valve timing as also mentioned. Does this engine use a MAF? I don't think mentioning the brand will be an issue and may help. I had a 3.0 Taurus that would eat one lobe of the camshaft although it would idle smoothly, any attempt at acceleration met with similar results. Of course old 60's small block Chebbies would do that too. Check engine light on??

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its a 1991 ford aerostar with a 4.0.i got the ford cord for my scanner today.scanner shows no codes.the check engine light is off.these things are well known for blowing head gaskets but the oil on the dipstick looks good and no bubbles in the radiator.i thought maybe clogged cats so i dropped the entire exhaust at the manifolds,no difference,still 3-7 pounds vacumn.the design of this van places the fi up against the bottom of the van,its very hard to look for busted hoses or other things out of place. the ticking noise turned out to be a rattle in the cat probably caused by the rough idle.

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Ooh, that doesn't sound like a lot of fun to work on. The 3.0 and 4.0 aren't related but anything is possible. Maybe a long shot, but does this have the TFI style ignition? It is a thin electronic module, maybe 1.5"w x 4.0"l x .5" thick attached vertically to the distributor. Those can go bad but not all at once. They may give a warning such as a bad miss climbing a hill or other odd behavior. I have replaced a handful of them on Escorts to Tauruses. Good unit but does have a lifespan, sort of like the crank sensor. I don't think that model uses a MAF, batch fire speed-density only, but could be wrong.

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Oops. I looked up the 4.0 in the Aerostar and it's the same as the Ranger. Should have similar ignition to our Buicks, waste spark, MAF etc. The one item I had go bad was the vacuum operated EGR. Not uncommon. It will kill manifold vacuum if stuck open like I had happen at low and idle speed. That also has the effect of making the power brakes very weak, especially on initial running. I fabricated a temporary metal gasket to go between the valve and the tube leading up to the intake. It was stuck partially open so removing vacuum connection from valve had no effect.

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Oops. I looked up the 4.0 in the Aerostar and it's the same as the Ranger. Should have similar ignition to our Buicks, waste spark, MAF etc. The one item I had go bad was the vacuum operated EGR. Not uncommon. It will kill manifold vacuum if stuck open like I had happen at low and idle speed. That also has the effect of making the power brakes very weak, especially on initial running. I fabricated a temporary metal gasket to go between the valve and the tube leading up to the intake. It was stuck partially open so removing vacuum connection from valve had no effect.

thanks.i'll check it.i have had loss of power brakes.

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thanks.i'll check it.i have had loss of power brakes.

With vacuum that low, it's no wonder. Mine was around 9" of vacuum and sounded like it had a huge cam at idle. Very bad rolling idle. Blocking off the EGR had vacuum of 20"-21"Hg. I couldn't get any of it apart so I replaced the valve and the tube from the exhaust manifold (Ebay) as well as the vacuum control valve up near the intake manifold. I had to get to some of it through the left wheelwell. Hope this helps.

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Sorry to mislead you. I see what you mean about the lack of EGR. At least it eliminates that issue. My '97 Ranger (last of the pushrod 4.0's) also have issues with the intake manifold gaskets where the upper and lower bolt together but that shouldn't give vacuum readings like that. It sounds like the original suggestion of valve timing or sticking is in play. I am not certain what dead miss on the ignition would do to vacuum? It does have the waste spark system like the Buick

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