Øyvind Aasvang

Hi all
I have an 84 Buick Electra Estate Wagon With 307 Vin Y in it, 70k miles
And it misfires, but only noticeable in Lock-up.
I have changed O2 sensor, cap, rotor, plugs, wires, coil, ignition module, even the carb, TPS and EGR
Idle speed set to 550 rpms in drive, ignition is at 22 degrees.
The AIR-system is disconnected/removed by me, this redused the misfireing some, but not all of it. I belive doing so removed a "vacuum leak" in the air-diverter.
I belive it's running in "closed Loop" from startup, it opens for EGR flow right away after starting.

Cruising Down the highway I notice the car sometimes gets more powerful, I've also noticed when warming up With the choke still partially on that it suddenly revs up conciderably. I belive that when I'm out driving and make a stop somewhere, stop the engine and restart, it's more powerful, like I've reset something in the ECM.
It's hard to maintain 60+ mph, it just seems to be lacking Power. In Lock-up it pulls itself on the flat road but a small Climb or a headwind makes it slow Down.

It runs average 17 mpg

I really hope someone can help me
Thx

pavemobile

If you haven't already checked this; under the carb primaries, when fully open, you will see 2 EGR tubes...these can fill with carbon to the point of fully clogging. The intake passage that feeds flow to these tubes can also clog; I fought that monster in the past. Just a deep socket is all you need (after carb removal of course) one is bigger than the other. The Olds 307 ECM tune is very sensitive to EGR flow, just a thought...and a little keyboard troubleshooting. Might be worth a look.

Øyvind Aasvang

Thanks pavemobile
I'll look into that. But I suspect it gets a little too much EGR, it has a little hesitation when i start to accelerate, and it's more powerful if i block the passage between the manifold and the EGR-valve. But then I get the pinging of course..

jcdynamic88

that increase in revs when the choke is still on is probably the ecm going into closed loop and advancing the timing.has the timing been set properly?

Sugar Bear

The low power could be a catalytic converter starting to clog. They often gave a moaning sound near the right front floor and the air filter would get sooty.

Øyvind Aasvang

Yes I kinda suspect the EMC lives a life on it's own. It's also noticable when i drive, as the Power suddenly comes back for a period

Øyvind Aasvang

Catalytic converter is removed. And, as I understand, that can make changes in the exhaust backpressure and can cause uncorrect EGR-operation.

jcdynamic88

the ecm is supposed to keep the timing retarded initially to make the engine warm up faster,when it reaches a certain temp it goes into "closed loop" and starts advancing the timing.has the initial timing been set?are you running the stock quadrajet? without a cat the idle mixture screws should be accessed and adjusted.

Øyvind Aasvang

Yes, jcdynamic88, you're right. I had a quick check on it just now, and it increases the revs when it's warming up. Also it kept the EGR-vacuum closed until it revd up, probably going into closed loop. But I think it was abit early, it only ran for maybe two minutes befor going into closed loop. The initial timing is set to 22 deg. And it's a stock q-jet, never been used (so it's not adjusted for this engine). It has the same numbers as the original one, but I guess the idle mix should be adjusted. When I accelerate it's kinda slow from 0/3-1/3 throttle, on 1/3-2/3 throttle it gets more power, and even more when the secondaries open. I assume this is because above 1/3 throttle the MC-solenoid doesn't adjust Fuel/Air-mix?

jcdynamic88

one of the more common problems i remember from that vintage olds is the vacuum line to the map sensor (on passenger inner fender) would frequently get melted by an a.i.r tube and either not allow vacuum to pass thru or it could even hold vacuum.the tube looks like a wire and is in the harness that goes over the passenger valve cover.i've also had bad map sensors that wouldn't set a code/light because it was stuck voltage wise within the parameters the computer was looking for.is this still computerized?

jcdynamic88

scratch that last question

Øyvind Aasvang

Yes, I've checked the MAP-sensor. What puzzled me when i checked it was that it gave the voltage reading opposite to what i read it was supposed to. I dont'remember now if the voltage should increase or decrease with more vacuum, but it struck me as strange that it performed opposite to what the internet told me it should. But I got a fault code when I unplugged it.

I'm also thinking about the coolant temp sensor, as the car seems to be going in and out of closed loop during driving. If it's dodgy and confuses the ECM.