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Now that the ECU is working I'll do that first, thanks. From fully warmed up, stop at a traffic light it takes a few seconds at idle for the engine light to come on.
Maybe if I can figure out how to avoid traffic lights this wouldn't be a problem.
Should be able to idle for a few minutes before any codes set in the system.
Probably a good idea to check ignition timing. might pay to check TDC on the balance is actually TDC.
I thought of another couple things to check which 'could' potentially cause the Check Engine light to flicker. Is your Air Pump and A.I.R. system in-tact? It's possible it could also cause some flickering
The A.I.R. system (pump/diverter/AIR tubes/Check Valves, etc) should pump a little fresh air into the exhaust stream at idle to re-burn any unburnt fuel ...to raise the temperature of the catalytic converter (where it's at it's most effective Temp range). It also helps keep the O2 sensor a little warmer too. The O2 sensor needs to be a minimum temperature of 600*F to start generating a mv signal between 100 (lean) to 900 mV (rich) to the ECM. You can and should measure with a meter at the O2 wire. You can observe at the scanner too, but the scanner is the ECM output, not the sensor output. 450mV is the middle ground and the reading should flip-flop rapidly above and below 450 mV between rich/lean (which you'd see on a scanner). The AIR tubes can rust at the base where they go into the exhaust manifolds and the check valve rubber seat at the top can burn-out from exhaust heat (over time). If that happens then some exhaust diverts back through the AIR system, and reduces the amount that the O2 sensor reads. The same thing is true for most EFI and new vehicles, where an exhaust leak 'can' reduce exhaust flow going past the O2 sensor and throw off it's reading and affect the reading the ECM is 'expecting'. So worth checking the air injections system. AIR tubes and the check valves are pretty cheap to buy new these days. When I was young AIR tubes were like $90 ea. now they're like less than $20 ea aftermarket and the check valves like $10.
Even "IF" the air pump system is not operating properly, ....let's say, your car can still operate fine as long as all exhaust goes through the exhaust manifold (not blowing out of exhaust leaks). I drove a Caprice for 150k miles with a non-working air pump and plugged AIR ports (plugged at the manifold). I was young and didn't understand what all that stuff did. It was expensive back in the day to buy those from GM parts. But the engine ran fine with no real problems for year. Yes, the Check Engine light did flicker at idle once in a while at idle. I wouldn't advocate taking that stuff off and I myself have returned most of it to OEM state. I owned several 80's caprices and the CCC system was really robust on all of them ..so long as it was maintained. On my 81 Corvette I have kept all the emissions in-tact.
Regardless, the GM emissions manual clearly states that for 1981's the O2 sensor can and often cools down below 600*F during idle (my car often does) dropping the mV reading, and the Check Engine light may flicker (and will run in 'Open Loop' temporarily). My 81 Caprice runs in open loop at idle but quickly goes into closed loop 2 seconds off idle. Maybe with a new O2 sensor it wouldn't do that, I haven't tried one. They're cheap. There is a conversion some guys used to do to install a newer (multi-wire) 'heated' O2 sensor in the system. I haven't done that though.
Other things to look at are vacuum leaks (with a vacuum gauge), double-check the ohms on the temp sensor, and match the reading up to the table per the ambient temp (when it's cold). It's worth removing the EGR and check underneath for it being plugged with crud (clean with a screwdriver). Then make sure the EGR pulls 'up' momentarily the moment it's started. Make sure the PCV valve is good and the grommet on the valve cover isn't cracked. The purge valve canister hose (to the carb) should be good as should the rest of the charcoal canister hoses.
But inspect the AIR system, check/change the O2 sensor too.
I thought of another couple things to check which 'could' potentially cause the Check Engine light to flicker. Is your Air Pump and A.I.R. system in-tact? It's possible it could also cause some flickering
The A.I.R. system (pump/diverter/AIR tubes/Check Valves, etc) should pump a little fresh air into the exhaust stream at idle to re-burn any unburnt fuel ...to raise the temperature of the catalytic converter (where it's at it's most effective Temp range). It also helps keep the O2 sensor a little warmer too. The O2 sensor needs to be a minimum temperature of 600*F to start generating a mv signal between 100 (lean) to 900 mV (rich) to the ECM. You can and should measure with a meter at the wire. 450mV is the middle ground and the reading should flip-flop rapidly above and below 450 mV between rich/lean (which you'd see on a scanner). The AIR tubes can rust at the base where they go into the exhaust manifolds and the check valve rubber seat at the top can burn-out from exhaust heat (over time). If that happens then some exhaust diverts back through the AIR system, and reduces the amount that the O2 sensor reads. The same thing is true for most EFI and new vehicles, where an exhaust leak 'can' reduce exhaust flow going past the O2 sensor and throw off the reading the ECM is 'expecting'. So worth checking the air injections system. AIR tubes and the check valves are pretty cheap to buy new these days. When I was young AIR tubes were like $90 ea. now they're like less than $20 ea aftermarket and the check valves like $10.
Even "IF" the air pump is not operating, let's say (for argumentive purposes), your car can still operate fine as long as the exhaust is NOT being diverted (...all exhaust goes through the exhaust manifold). I drove a Caprice for 150k miles with a non-working air pump and plugged AIR ports (plugged at the manifold). I was young and didn't understand what all that stuff did. It was expensive back in the day to buy GM parts. But the engine ran fine with no real problems, but the Check Engine light did flicker at idle once in a while. I wouldn't advocate taking that stuff off, I've returned most of it to OEM state. On my 81 Vette I have kept all the emissions in-tact.
Regardless, the GM emissions manual clearly states that for 1981's the O2 sensor can and often cools down below 600*F during idle (my car often does) dropping the mV reading, and the Check Engine light may flicker (and will run in 'Open Loop' temporarily). My 81 Caprice runs in open loop at idle but quickly goes into closed loop 2 seconds off idle. Maybe with a new O2 sensor it wouldn't do that, I haven't tried one. They're cheap. There is a conversion some guys used to do to install an 83 or up 'heated' O2 sensor in the system. I haven't done that though.
Other things to look at are vacuum leaks (with a vacuum gauge), double-check the ohms on the temp sensor, and match the reading up to the table per the ambient temp (when it's cold). It's worth removing the EGR and check underneath for it being plugged with crud (clean with a screwdriver). Then make sure the EGR pulls 'up' momentarily the moment it's started. Make sure the PCV valve is good and the grommet on the valve cover isn't cracked. The purge valve canister hose (to the carb) should be good as should the rest of the charcoal canister hoses.
But inspect the AIR system, check O2 sensor.
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I've removed the seized air pump EGR and all associated equipment. I'm only interested in the performance and economy aspects of the ECU: adjusting AF mixture, advancing the timing, and lock-up of the torque converter. I realize that increasing oxygen content into the exhaust manifolds can heat up the O2 sensor to avoid triggering the check engine light but there are simple work-arounds for that.
Do I care about reducing emissions? Of course but to a point. Back in the 80's (college and the beginnings of my career= poverty) I had a hand-me-down '72 model car with a 351 V8, a two bbl carburetor and points ignition. I think there may have been an air pump on it when new- my Dad was the original owner, but if so he quickly yanked it out. There never was a catalytic converter. In '84 I worked for the DOT in Hartford CT and, being an urban setting, all the counties required annual smog testing. This wasn't a visual inspection of your equipment but a performance oriented one where they sampled your exhaust with a probe. Since I always kept my car in a state of perfect tune and made sure the engine was good and hot, the test came back basically zero. I was burning all the fuel completely.
That's my goal, emissions-wise, with this car: perfect tune. I plan on removing the cat- it's probably plugged solid, getting rid of the stupid Y to Y pipe and installing true dual system with either an H or X equalizer.
Check/change the O2 then, maybe a new one will bring the mv rage up ...or else just live with a flikering light at idle. It's normal anyway. As long as it goes out off idle.
You can check the cat for being plugged (or not) on the vehicle. I think I read the number was above 2.5 PSI = restricted. I can check that. You could put an accurate psi gauge on it (at the top of the AIR tube). Also if the manifold vacuum can't be reached it could reflect a plugged cat. That's why it's so important to know the vacuum. The cats weren't as restrictive as guys used to think back in the day (lot of urban myths back then). The newer element cats are really almost no restriction. Makes a big reduction in emissions.
Not preaching but removing the cat gives classic car owners a black eye, and amunition for greenies to point fingers at the hobby. I know most guys don't care, but it IS something to consider, considering there've been significant lobbying efforts on the behalf of SEMA to keep regulatory efforts off the backs of the classic car hobby/industry.
The biggest downfall of the bead converters is they were HEAVY. Really heavy.
Thanks for your help Mark. I don't see many Greenies at car events so that's not a concern of mine. The exhaust sounds crappy with the Y so it has to come out. No way am I going to buy two cats. The car will be driven little anyway so that would be a waste of resources with little, if any, return.
The price of a new Bosch O2 sensor was only $24 over the counter so figuring the old one was nearing 40 years I bought one and put it in. The old one loosened easily but got harder to remove as it turned and messed up the threads. It took a half-dozen tries to start the new one in using only hand pressure but still became cross-threaded to fully seat. I was careful and able to compress the metal gasket, so it doesn't leak.
The result is basically the same as the old sensor, check engine comes on unless the engine is hot.
Chalk another one up to "don't throw parts at it". Damn, will I ever learn?
I have an appointment next Wednesday to get the cat removed and switch from a Y to an X pipe.
Did you check the stored codes to see why the light is coming on?
even though the new o2 sensor didn't seem to change anything it may still help it run a bit cleaner (not that we are in this hobby for that)
just to be clear removing the cat won't cause more codes but it should improve performance especially if it's the original one.
Try putting the EGR back on. The EGR helps lower upper cylinder head temps quite a bit. See what happens. Make sure the diaphram is good and the pintle clean.
Did you get your Monitor 85 scanner to read the ECM?
Yadkin
If you're comfortable with the OTC platform and looking to add a little more capability, I saw a Monitor 4000E that might go cheap on Ebay. The later versions show a few more data points per screen, easier to see what's going on: https://www.ebay.com/itm/Monitor-400...s/233525486742
For scanners on legacy vehicles, however, I would recommend the old-school Snap on MT2500 (or a newer SO scanner). The reasons I say this are:
The Old-school MT2500 provides 9 points of data per 'viewable' screen, and you can scroll down for more info. It makes it easier to compare readings from different sensors, etc. Nine pts of data is actually more data points on a single screen than a newer Solus Ultra believe it or not (on one screen). The MT2500's are inexpensive to buy nowadays. They were ahead of their time.
Even new Snap On scanners come with legacy software which can scan vehicles back to 81. So, if you had other cars/trucks you wanted/needed to scan, one scanner would do it all (although you need a special cable to connect with OBD-1 style connectors).
Bi-directional capabilities - Not a big deal with 81's (although you can activate the 'purge valve' I believe). But on newer vehicles the scanner can program fobs (in most cases), program new radios, ABS & Airbag modules, do gauge sweeps and a lot more.
But for just doing the 81 Vette, an inexpensive MT2500 kit with old cartridges would provide many data points easier to access which might help your troubleshooting process.
Did you check the stored codes to see why the light is coming on?
even though the new o2 sensor didn't seem to change anything it may still help it run a bit cleaner (not that we are in this hobby for that)
just to be clear removing the cat won't cause more codes but it should improve performance especially if it's the original one.
I'm big on low emissions, not just for the obvious reason but because a clean running car is a well-tuned car.
Prior to getting the CCC fixed and talking to the carb and dizzy the car ran filthy rich. The smell of unburned gas is unmistakable. Having been run like that by the PO for who knows how long I'm certain that the cat is plugged full. I will do further tuning and troubleshooting after I get that taken off on Wednesday.
It happened to me years back with an '81 Ford Escort. It was a beater but ran well until the electronic carb started running rich, gas mileage went down then no power after about 2000 RPM (which was most of the time with how I drove it). With that car I removed the cat, busted out the inside and put it back on, and it ran great. Still rich but served its purpose.
Try putting the EGR back on. The EGR helps lower upper cylinder head temps quite a bit. See what happens. Make sure the diaphram is good and the pintle clean.
Did you get your Monitor 85 scanner to read the ECM?
.
Thanks for your advice Mark but I'm going to wait util I get the exhaust flowing freely before I toss in more variables. Once I do I'll re-check the timing, check to see if it is advancing properly (it 'feels' like it is) and make sure that my scanner is conversing to the CCC properly.
The exhaust work has been delayed because the shop's having trouble sourcing an X-pipe due to this virus thing, and they don't want to make it themselves. I took the car out for a 30 minute joy ride earlier today and it ran great, engine light turned off as soon as I was 1/4 mile down the street and stayed off. No power at all over 3000 RPM which I assume is the clogged cat. No stink at all cooling off inside the garage.
New X pipe installed, Cat removed. The pavement was a bit wet this afternoon driving out of the shop. I was doing about 40, stepped on it and the rear tires spun.
