Won't Rev. Help!

[RoyBatty]

Have you determined which cylinders are misfiring? Or are all of them running the same?

[majicwrench]

Save your strength. Does it still run well with the return line pinched?? If so, injectors can deliver enough fuel, cam timing is close enough, ignition timing is close enough, cam lifters etc are fine.

Tis not getting enough fuel. OR is getting too much air for the fuel. Are you dang sure all the air is going thru AFM?? Unmetered air will make it run lean. Not familiar w Spider air intake system, but try pinching off the various hose that go to the big duct. Is duct in good shape?? Flex it, look for cracks.

And if it revs w return pinched is NOT your exhaust. But if you ever do have to check it, it just takes seconds to drill a hole, test backpressure, and put sheet metal screw in hole. It's the way proffesional mechanics do it.

[RoyBatty]

Disagree,
It is not wasted time to determine whether or not it's just one cylinder or all of them. Knowing he had had the engine out and fuel lines disconnected, it is not out of the question that one or more of the injectors is partially obstructed. Improper flow from the injector s can cause misfiring.
An easy way to check for a cold cylinder is by hitting each exhaust port with a stream of water from a spray bottle to compare how fast the water burns off. The cylinder that burns off the water the slowest is likely where you need to start.
The amount of blockage needed to cause problems is minuscule.

[majicwrench]

I'd agree with you but then we would both be wrong

It is not one cylinder. You could smash the gap on one plug car would still rev, still get up to speed.

I like the spray bottle/water bit, I usually use a non-contact thermo gun, but water would work well if you had one dead missing.

[chrisfiat]

17 inches of vacuum is not right you should be at least 20to 23 at idle, possible plugged cat or a large vacuum leak. loosen up the flange to the converter and see if vacuum improves, spray some carb cleaner around all areas of the intake where there are seams or gaskets or vac lines , any potential leak area, to check for a change in engine running, do this carefully car cleaner burns. also check to see if the intake tubing from the air meter to throttle body is properly fitted and not cracked or broken

[wizard124]

Hey, i like all the input!

i definately have a miss. Rough idle and miss. When i open the throttle butterfly at the plenum, it revs to about 2500 and begins to bog down. At this point if i jiggle the throttle plate, i can work the higher revs but it isnt smooth. not much difference if i pinch off the fuel return line or not.

[DanD]

You should have no problem revving an engine to almost any RPM in neutral. I'm thinking that the cam lobes on #4 should look to be at 10 and two o'clock when timing marks are lined up.

When you test for fuel pressure, are you testing on a running engine ? A constricted filter or fuel line can deliver static pressure but not meet flow requirements.

[wizard124]

I re-inspected the air tube. OK
Fuel pressure an flow. Pressure regulator all check good.
Double checked cam marks with TDC; as close as the toothed wheels allow.

I think my next check will be the AFM sliding contacts. Then start pulling injectors.
This is past fun.

[RoyBatty]

Scroll down this page to just past the halfway point.
http://www.hiperformancestore.com/Ljetronic.htm

[chrisfiat]

Hey, i like all the input!

i definately have a miss. Rough idle and miss. When i open the throttle butterfly at the plenum, it revs to about 2500 and begins to bog down. At this point if i jiggle the throttle plate, i can work the higher revs but it isnt smooth. not much difference if i pinch off the fuel return line or not.

so did you disconnect the converter to see if vacuum / running improved?

[wizard124]

Hey, i like all the input!

i definately have a miss. Rough idle and miss. When i open the throttle butterfly at the plenum, it revs to about 2500 and begins to bog down. At this point if i jiggle the throttle plate, i can work the higher revs but it isnt smooth. not much difference if i pinch off the fuel return line or not.

so did you disconnect the converter to see if vacuum / running improved?

When my cat was replaced, the muffler shop took out the flange and straight welded it. But, removing the O2 sensor to relieve pressure made no difference.

[wizard124]

I am starting to think I may have a bad Ignition Control Module.

The car never had the "engine just dies but starts up awhile later syndrome" I've been reading about. But it would do an occasional, brief engine miss/performance loss hiccup.

Thoughts?

[azruss]

my experience is that the module either works or doesnt. You may want to look at the mag pickup. The wires under the cap can be an issue, even if everything looks fine from the outside.

[DanD]

my experience is that the module either works or doesnt. You may want to look at the mag pickup. The wires under the cap can be an issue, even if everything looks fine from the outside.

Yes, those wires can get weird with the vacuum advance shifting them around. The insulation can look great, but the wire inside can be corroded to dust.

[DanD]

When my cat was replaced, the muffler shop took out the flange and straight welded it. But, removing the O2 sensor to relieve pressure made no difference.

Your exhaust is almost 2 inches in diameter. Your O2 sensor is a hole the size of a spark plug. Respectfully, I don't think this is a fair test. You said vacuum goes down to almost zero when you rev it and run out of power. If that is true, it sounds like your engine can't draw any air. If no air can get out, no air can get in. It may seem like a pain to disconnect the cat, but it might eventually have to be done.

Also, if you do not know how old the fuel filter is, replace it now. Then get some Deoxit D5 from your local Radio Shack, and go to town on all those little connections you took off, using the D5 and a tooth brush. Include the grounds. I have seen perfectly good temp sensors fail to function because of oxidation inside the connector, which looked fine to the eye.