Hi all:

1985 245. I've been working on this car for 8(?) months+ with time out for lymes (I don't recommend it).
it's finally running but doesn't handle increased gas. Distributor rotation doesn't fix it. Fuel pressure is about 30 at the rail and doesn't drop on acceleration. There's soot in the exhaust. The Cat converter had disintegrated and was empty. There's a signal at the distributor. Both computers are replaced, there's a small 3rd one under the glove box but it looks new so I haven't messed with it. I found several air leaks but the change was minimal, a leak would have to be huge to have that much effect (judging by the effects of the small ones). The vacuum lines test, unless there's some I haven't found. The gas has been replaced but is still dark. I'd be grateful for any suggestions.

I'd start with Intake manifold gasket, FPR, AMM. AMMs fail in varying ways.

A few years my car wouldn't stay running. Unplugged the AMM. Started easily but lacked power on the way home; Last year same no start. Had to keep the revs up to get out of the parking lot. Ran great at speed but would die below ~2000 RPM.
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240 drivers / parts cars - JH, Ohio

Thanks. FPR is good (rail pressure is constant 30 lbs), I'll check the gasket after the AMM is verified. I thought an AMM was a MAF, WTF!

I see MAS (Mass Airflow Sensor), AMM (Air Mass Meter), MAF (Mass Airflow Sensor), Hot Wire MAF; and I think there are others. I think MAF is the generic term. Maybe most correct but I rarely see it here. FCP lists it as a "Mass Air Flow Sensor".

I think I've had FPRs w/ good pressure that were bad.

I've seen a lot of vacuum leaks in the last 2-3 years.
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240 drivers / parts cars - JH, Ohio

I switched out the fuel pressure regulator and the problem persists, but I noticed when the fuel line nut was first cracked, there were bubbles in the fuel rail. Seems like that shouldn't be a unique problem but maybe if the bubbles were big enough they could affect all injectors at the same time and cause jumpy acceleration. so ... a loose hose fitting between the tank & fuel pump?

bubbles in the fuel rail. Seems like that shouldn't be a unique problem but maybe if the bubbles were big enough they could affect all injectors at the same time and cause jumpy acceleration. so ... a loose hose fitting between the tank & fuel pump?
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The hose on the intank pump is cracked or crumbling?

Art's pic

http://cleanflametrap.com/transferPump_files/image055.jpg

1. Bubbles in fuel: Pull the feed at the sender and blow into it against the pump. And/ or disconnect the feed at the rail, attach a clear hose, jump the main pump and see if you're getting bubbles. I've had pinholes in the curved pipe coming off the sender; and cracks in the rubber hose.

2. Vacuum leak: Spray water around the intake and see if there's any change. Check the hose to brake booster.

3. When I've had low power it's been a restricted fuel filter - but that bucks under heavy load; or audible vacuum leaks; or a failed MAS

4. Compression, plugs, wires, etc are good? No chance it jumped time?

(I don't know much about the earlier cars. I try to stick to 1989-90)
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240 drivers / parts cars - JH, Ohio

all that stuff is clear, I found a leak between the main & in-tank pumps that was drawing air, it's fixed but still runs badly. what would cause it to "jump idle"?

I have been trying to follow your posts but I have to admit your descriptions are a bit jumpy too!

First it is jumpy acceleration and then there is jumpy idle. You still had dark gas after replacing it...?That's pretty hard since unleaded fuel is clear.

You have me looking at the jumps you made while changing components to have them not work.

My overall conclusion is that jumping is not going to make the car stop twitching. Just try some plain ole-back-to-basics repairing.

Start with a good ignition repair. New parts removes the guessing. A miss fire will make "several" adjustments take place within the engine management system "so fast" that it's all you are going to do is hide and watch!

Back to fuel being bad. Dark can be rust or jelly. I do not know where you have "seen" this but it can be a nightmare movie on anybody's radar!

Low fuel amounts from contaminants will mean lean mixtures!

A lean mixture is very erratic or unstable by its own nature compared to an overly rich mixture that smolders and languishes. A rich type of condition is out of the perimeters of any quick responses from the engine management system. There by, no jumpy things from rich mixtures. IMHO!

Sorry about saying things that may offend you but I felt you needed a little tilt put under your playing field by now.
Go to FAQ's on what if my engine needs a tune up after sitting. Something along those lines.

Phil

Yes, you have been having trouble following. "jump idle" was jon-h description, my question was in reply to his thread. don't read too much into it.

Ok if you say so.
I thought I tagged the post for May10 and was working with dark fuel.

A statement by you later used "jumpy" in limp mode while testing the AMM. I think Jon and you were thinking a like and he put that there later. Its ok, as it's all small potatoes in the big picture.

I wanted to tilt our heads a little, stand on one foot and rub the top of our heads, if it will smooth out YOUR engine.

The management system "has to" deal with a properly ignited fuel charge in order to not get jumpy!

I see fuel lines, vacuum lines and part changes appearing from back end to front end. Change on some but you are getting frustrated after this amount of time. Sorry about the time out you had with lyme. That is tough stuff.

May I suggest that a simple bad rotor button can do some of the weirdest things.

A distributor cap shows its ugly face but terminals can be cleaned. Unless its cracked moisture is about the only thing that brings out a grin with them.
Same for wires but they can have even more sporadic things going on internally. Unique materials used to contain the physics of transferring electricity. Doing this is a science all to itself.

Ignition components are expendables for reasons why not give them their space as being a weak link.

To add one more item in the mix of chatter I am doing throw in a timing belt off one tooth. Lots of documentation on those.

Nothing can disturb air flow more to other cylinders than ill timed valves or a unpredictable throttle position change on the management system.
93's got different TPS's at the end of life of the 240 to get finer detail.

A manifold leak that another posters passion for a hot pick.

Here for what its worth.
Phil

it's too dramatic, nothing subtile like low power. with gas, the timing light flashes 20 deg+ off and farther so it misses that cycle, when it slows down it fires again in half second spurts, the more gas the louder and longer between spurts. I found a used knock sensor that I'll try out tomorrow.

Thanks, I'll try that. how does it jump time? the timing light goes crazy when it bucks.

I replaced the submersible hose ($30 for 4 inches), maybe the hose clamps weren't tight (?) I totally love to do stuff over (and over).

if you replaced the hose, then that's prob not it.

I found an air leak in the tank & the in-tank motor wasn't working, that's fixed but the motor still runs badly. what's the symptom of a bad knock sensor?

I just swapped with one from a running 86 (same numbers on the side). there was no difference in acceleration.

Symptom sounds like a failed AMM swap in your spare known good one.
Dan

I disconnected the AMM but it's still jumpy in limp mode.

If it runs fine at idle that is limp home mode. You can drive it being light on the throttle but it is not going to accelerate normally because the AMM is not working as it should and computer is in a default mode.
Dan

I just swapped one from a running '86. it ran no differently

That makes sense, I'll find one that runs and try it. I'll let you know.