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Low and bouncing vacuum, when warm?


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88 Comanche, 2.5, 4spd, no A/C

 

Been working on getting the new motor installed. It seems to run real good until the engine warms up. It starts and idles fine when cold, shows about 16 in.Hg vacuum with a steady needle. As the engine warms up, about 3 minutes, the vacuum will drop to 10-8 in.Hg. and bounce like a blurr. The engine seems to drive fine but if you lift off the gas when coming to a stop the engine will stall. You can start it and it will idle fine unless you punch the throttle off and on.

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I pulled the vacuum line on the EGR and noticed there is no vacuum present in the idle condition, should there be? Good point on the O2 sensor, I have noticed the idle searching up and down a bit. I put a timing light on the engine and saw the timing @ 10 degrees, that is really not adjustable. At this altitude a little extra timing is probably OK and lower vacuum is normal. There are only 42 miles on the engine now, it will take a while for things to settle out and break-in.

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Oh.......there are only 42 miles on the engine??

 

I missed that :doh:

 

The engine is not even started to be broken in yet. You still running break in oil???

 

Get some millage on that new engine, and then see what it does.

 

Your dealing with a new born baby there, and once you get it out of diapers, then the fine adjustments can be made.

 

I did miss the point that your in that "lite air" area, and I'm thinking there both a 02 sensor, and IAC for them "lite air" running conditions.

 

Yes, the timing is not adjustable, and 10* BTDC sound correct, the timing is adjusted thru the ECU, and more ""Tuned"" after the engine hits operating temperature.

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I'm not running any special break-in oil, just 5w-30 and a Mobil1 oil filter. I got the engine from AutoZone, Proformance is the builder in Springfield, Mo. They look like a pretty good operation, lots of ISO certifications and process controls. They are a teir 1 engine supplier to Chrysler for remanufactured engines.

 

One thing I need to understand is the EGR valve circuit. What triggers the solenoid to open and close the EGR valve? I'm not sure if mine is working properly, when I apply a vacuum source to the valve there is no change in the engine RPM?

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I'm not running any special break-in oil, just 5w-30 and a Mobil1 oil filter. I got the engine from AutoZone, Proformance is the builder in Springfield, Mo. They look like a pretty good operation, lots of ISO certifications and process controls. They are a teir 1 engine supplier to Chrysler for remanufactured engines.

 

One thing I need to understand is the EGR valve circuit. What triggers the solenoid to open and close the EGR valve? I'm not sure if mine is working properly, when I apply a vacuum source to the valve there is no change in the engine RPM?

 

Was the engine broken in from the rebuilder?

 

What type of 5w30 you running? Synth? Dino?

 

Rob L.

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I don't think the engine was actually broken in, they did some pressure testing and a short spin up for compression check. There is some special testing on high-end motors where they will actually run them on a dyno, I doubt my $1400 2.5 AMC saw any of that testing. Here is a clip on the factory testing from their web site.

 

100% Functionally Tested

Before it leaves the factory, each PROFormance engine must pass multiple levels of rigorous testing. All complete engine assemblies are pressure tested to ensure that there are no leaks internally or externally within the cooling system which verifies that the cylinder heads, expansion plugs, and water passages are properly sealed. All units are 100% functionally tested for oil pressure, oil flow, and compression. Advanced testing includes live fire testing of fully assembled engines and their components and dynamometer testing under varied and extreme conditions.

 

I'm using the old fashion dino juice, I have heard that synthetic oil is not a good break-in oil on the old technology engines. Chevron Supreme, API service SM.

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Yup, you hear right on the dino oil, what's the spect's from the builder, change at 300 miles, then again at 1000.....or something like that???

 

The more reply's you make, the more info we find out :doh:

 

Rebuild from Advance.......that's a long block, correct???

 

You had to bolt on the manifolds???

 

Did you bolt on the intake as per spects???

 

Your waving idle/vacuum could be from leaks on the intake manifold.

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

 

 

Get some mileage on the engine before you start tearing apart things.

 

 

About 1/2 way down this page is the test for the EGR solenoid and valve -

 

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

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See..........time and mileage on a re-man engine, takes some time to "break" in.

 

It's not like a new drill motor, you take it out of the box and plug it in, and it works :eek:

 

Engines take a little more time to work out their bugs, and seat, and now that your still breaking it in, keep the oil changed!!!!!

 

Check back after you crank on another thousand miles to see if your vacuum problem is still there :D

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