77' 280 acceleration problem

[brento_1488]

hey guys, baught this 280 from a lady who baught it off the lot in 77. one owner, she "drove it till it stopped running." well its running now.

but im kinda goin nuts on what the deal is now

put it in gear and accelerate and it doesnt run right. backfires (through the intake) and doesnt want to rev past 3000.

thought it was the coolant temperature sensor. orderd a new one that wasnt it...

ive lurked around threads to try and find the problem. no luck yet.

figured ide ask the pros and see what kind of help i could get in resolving my running problems.

thanks

Brento

[robftw]

Check and make sure you dont have a vacuum leak from the AFM to the intake manifold, could be your AFM too... Or timing

[cozye]

dont do anything else until you put a fuel pressure gauge on it. almost ALL of the EFI problems are related to fuel delivery, and perfect pressure is the key. A rusty gas tank, clogged filter, faltering pump, faulty fuel pressure regulator, etc.. can all cause your problem. There are lots of other causes too, but you can't even begin to go down those paths until the fuel delivery is 100% tested and verified.

[LeonV]

Did you get any moisture into the engine? If yes, the TPS is the usual culprit.

[brento_1488]

i appriciate it guys. any trouble shooting ideas??

[240260280z]

Yeah I am pretty sure it is the throttle vane switch (aka TPS) and it is easy to resolve. Check here and follow calibration procedure and you should be good to go.

The problem is that when this switch sticks in the idle position, the computer goes into coast-down mode when the revs are above 3000rpm and cuts off fuel until revs go below 3000. It is probably the world's first rev limiter albeit by accident.

http://atlanticz.ca/zclub/techtips/tps/index.html

[cozye]

The car will run decently without the TPS connected, if you want to rule that out you can just unplug it. If you are giving it a bunch of throttle without the TPS, it will be lean so just use partial throttle when trying it out. IT will give you something to do while you are waiting on your fuel pressure gauge.

[FastWoman]

The TPS is almost certainly the culprit with the rev limiting, but the problem suggests your computer is seeing the no-throttle condition, in which case there would be a slight idle enrichment. The "middle" position on the TPS, in which no contact is made, would be the leanest condition. Then at maybe 2/3 throttle you'll get a "full throttle" enrichment.

So considering that you're running lean (hence the backfiring), I suspect there's other stuff going on besides the TPS. But there usually is. In my experience, the most common problem on any old car is rotted vacuum hoses. If you go all over your vacuum spaghetti, I bet you'll find a few rotted hoses. I'd replace them all, so that you know they're good. Also look for cracks between the bellow-folds in the boots between your air cleaner and air flow meter (AFM) and between the AFM and throttle body. A crack in the latter one can result in unmetered air leaning your mixture. You could also have a leaking intake manifold gasket. A quick test of the tightness of your engine intake can be done very quickly with my "yogurt cup test" ™. See here:

http://www.google.com/search?q=%22yogurt+cup+test%22+site%3Aclassiczcars.com&sourceid=ie7&rls=com.microsoft:en-us:IE-SearchBox&ie=&oe=

And then there are other reasons for lean running. We'll discuss those with you after you've ruled out the simple stuff.

[brento_1488]

thx. im waitn on the fuel pressure gage to help narrow my search down too. ill start replaicin vacume and fuel lines for now.

in the mean time, i have a california 280. can i just pull all that california $^!# off? will the car run fine? i live on an island where we have no smog controll so im not to worried about smog

[FastWoman]

Well, contrary to popular belief, all that emissions junk does really make the engine run more cleanly and efficiently if it's working correctly. However, if it's in disrepair, it will screw your performance and smog up even worse than if you removed it. It's illegal in most states to remove or modify emissions equipment, by penalty of not passing state inspection -- and possibly fines imposed in some places???

It's a pretty safe bet that the BCDD on the bottom of your throttle body doesn't work. Most people remove and plate over that. Your carbon canister is probably fine, is required by law, and does nothing to dampen performance. Just check it out to verify it works and doesn't leak. Some people remove the EGR stuff, without much ill effect. That cleans up the engine compartment a lot. Some of your spaghetti might have to do with the A/C high idle and not emissions. You can do without the A/C high idle (which is helpful), but you can't do without the vacuum supply to your air handler, which controls heater doors and such. If you have an air pump (doubt it), that probably can be removed. Non-California 280s had no catalytic converter, so if you can make the "California" go away, I suppose you could remove the cat. I have no knowledge of the altitude switch and whether you could delete that. I think the throttle let-down dashpot on top of the throttle body is helpful if it works. It should have no tubes connected to it. I think that's all your engine compartment junk, but there might be something else.

[240260280z]

Did you try what Cozye suggested?

[brento_1488]

about the TPS? ya its not the TPS. like cozye said it ran decently with out it even plugged in. havnt had much oprotunity to work on it much more in the past few days.