Poor MPG. Tune-up suggestions?

[22229stingray81]

Geez, you're absolutely right, thanks! I was looking for a section called "vacuum motors" or something like that. Passenger side stays closed except at WOT. That makes things a bit easier. I'll report back after I do the test procedure; thanks again!


-Tatortot

 

[22229stingray81]

Okay, both motors passed the vacuum test. Also checked the vac hoses and all is well. So I guess the air temperature sensor is at fault. I'll do the engine warm-up test again just to make sure. Anyone have the part number for the AC Delco air temp sensor? I found 213116, but the online databases say it doesn't fit an 81 Corvette.


-tatortot

 

[Antz81]

Delco list 213-116 as being for 1984 only.
corvette america a temp sensor as being for 1980-86???
I have found other places that list the temp sensor you said (213-116) for a 1981
also found these two as listed for 1981 on ebay, but a cross reference with delco doesn't match:
ATS18 Chevrolet Corvette Pontiac GMC Air Cleaner Temperature Sensor 8997493 | eBay
Air Temperature Sensor Standard ATS7 | eBay
The ATS18 is listed on the standard brand website is being for an 81 Vette. Can't find a delco number though. but the cross-referencing this part on the delco website brings me back to 213-116???
It almost seems as if no-one knows (at least the suppliers anyway.)
213-118 (for 1982/4) & 213-117 (for 1980 5.0) also seem plausible (as per delco website)
213-118 is blue as the one on mine is but that doesn't mean it's right either.
Hope that makes some sense and doesn't just confuse you more.

 

[GerryLP]

Tattor,

Check the routing on the hoses between carb and temperature sensor, and between vacuum motors and sensor. If they are backwards or reverse routing, it won't work like it should.

 

[22229stingray81]

Makes perfect sense, thanks! It's exactly what I'm finding too. Rock Auto actually has a closeout one for only $7, but I question the reliability. It's made by BWD. I might end up having to go with the ATS18.

Delco list 213-116 as being for 1984 only.
corvette america a temp sensor as being for 1980-86???
I have found other places that list the temp sensor you said (213-116) for a 1981
also found these two as listed for 1981 on ebay, but a cross reference with delco doesn't match:
ATS18 Chevrolet Corvette Pontiac GMC Air Cleaner Temperature Sensor 8997493 | eBay
Air Temperature Sensor Standard ATS7 | eBay
The ATS18 is listed on the standard brand website is being for an 81 Vette. Can't find a delco number though. but the cross-referencing this part on the delco website brings me back to 213-116???
It almost seems as if no-one knows (at least the suppliers anyway.)
213-118 (for 1982/4) & 213-117 (for 1980 5.0) also seem plausible (as per delco website)
213-118 is blue as the one on mine is but that doesn't mean it's right either.
Hope that makes some sense and doesn't just confuse you more.

 

[22229stingray81]

Well, I went out today for a ride to see if the flap would open when warmed-up in the snorkel. BTW, Gerry, I checked and the vac line routing is indeed correct.

Anyways, right away I could tell something was up. I kicked the choke off, and it idled a little high. I went for a drive, and as soon as I gave it some gas, it acted like the choke was on again. I pulled into a parking lot, and I wiggled the choke coil power wire. Revved the engine and the rpm's fell to normal. Drove around a bit more, and the RPM's went back up. Pull over again, take the whole air cleaner off, and really tape it on there. Turned around to go home, and it came on again. Dig this though: I was at a stoplight, and it was idling high, again like the choke was on, around 1000 RPM in gear. Then, it suddenly, over the course of a few seconds, goes back down to normal idle. I get it back home, and cannot get it to replicate the problem. I guess the choke coil was sufficiently warm at this point? Even when I take the choke wire off, it was fine. Anyways, I attached a picture. You can see what a lousy state the connector is in, so I will replace it. Also, that vac line on top of the coil I moved to under the coil. I'll report back when I do some more testing.... I will say this though; I saw the snorkel flap open, so I think all is well in that respect. I'll do the test again, hopefully without the idle problem. Stay tuned!

-Tatortot

 

[Antz81]

Well, I went out today for a ride to see if the flap would open when warmed-up in the snorkel. BTW, Gerry, I checked and the vac line routing is indeed correct.

Anyways, right away I could tell something was up. I kicked the choke off, and it idled a little high. I went for a drive, and as soon as I gave it some gas, it acted like the choke was on again. I pulled into a parking lot, and I wiggled the choke coil power wire. Revved the engine and the rpm's fell to normal. Drove around a bit more, and the RPM's went back up. Pull over again, take the whole air cleaner off, and really tape it on there. Turned around to go home, and it came on again. Dig this though: I was at a stoplight, and it was idling high, again like the choke was on, around 1000 RPM in gear. Then, it suddenly, over the course of a few seconds, goes back down to normal idle. I get it back home, and cannot get it to replicate the problem. I guess the choke coil was sufficiently warm at this point? Even when I take the choke wire off, it was fine. Anyways, I attached a picture. You can see what a lousy state the connector is in, so I will replace it. Also, that vac line on top of the coil I moved to under the coil. I'll report back when I do some more testing.... I will say this though; I saw the snorkel flap open, so I think all is well in that respect. I'll do the test again, hopefully without the idle problem. Stay tuned!

-Tatortot

I've also had problems with the connector for the choke power coming off.
It makes the choke plate at the top of the carb close almost all the way. (once the coil cools)
On mine it seemed to make it idle low not high.
Just a thought here: i do recall you raising your idle as it was low in the past. This makes me wonder if you are seeing problems with that connector making idle at normal speed, and sometimes it making proper contact, allowing the coil to heat and then the idle increases due to the increase in air flow.
Definitely get a new connector on there and see what happens.

 

[GerryLP]

Well, I went out today for a ride to see if the flap would open when warmed-up in the snorkel. BTW, Gerry, I checked and the vac line routing is indeed correct.

Anyways, right away I could tell something was up. I kicked the choke off, and it idled a little high. I went for a drive, and as soon as I gave it some gas, it acted like the choke was on again. I pulled into a parking lot, and I wiggled the choke coil power wire. Revved the engine and the rpm's fell to normal. Drove around a bit more, and the RPM's went back up. Pull over again, take the whole air cleaner off, and really tape it on there. Turned around to go home, and it came on again. Dig this though: I was at a stoplight, and it was idling high, again like the choke was on, around 1000 RPM in gear. Then, it suddenly, over the course of a few seconds, goes back down to normal idle. I get it back home, and cannot get it to replicate the problem. I guess the choke coil was sufficiently warm at this point? Even when I take the choke wire off, it was fine. Anyways, I attached a picture. You can see what a lousy state the connector is in, so I will replace it. Also, that vac line on top of the coil I moved to under the coil. I'll report back when I do some more testing.... I will say this though; I saw the snorkel flap open, so I think all is well in that respect. I'll do the test again, hopefully without the idle problem. Stay tuned!

-Tatortot

The connector is available. I am not home. So I cannot look up the part number, but it is available.

 

[22229stingray81]

Already got it on order, Gerry

Of course none of the local places had it, so I picked one up on eBay.


-Tatortot

 

[Peer81]

The choke connector is a special model that clicks in place, it also has the L shape in the connector. The one you have one is a bubba solution.

As for the choke, was the engine compleetly warmed up when you set out for the drive? Because it sounds perfectly normal to me if the engine isn't compleetly warmed up (and it takes a while) that everytime you hit the throttle the choke spring will snap the choke on again.
If that isn't the case, first look for Lars his paper to setup the choke the right way. For example the startup choke blade opening has a big impact on rpm (when warming up). When the engine is warming up and the choke is expanding the mixture can go from rich to lean or visa versa everything is possible. When rich the rpm drops when you have a good mixture or even a little on the lean side the rpm is higher. That way I can be the case that from one time to the next rpm is higher then a few minutes before. Even if you have the choke just right then you have the air cleaner that is giving air that is warming up AND the amount of air is changing... That way its a miracle that the engine has a steady rpm when warming up

Greetings Peter

 

[22229stingray81]

Okay, I got the new pigtail all connected up and I'm getting 12 volts. Started up the engine and let the fast idle come up. Kicked off the choke and it appears to be operating normally again! Small victories

I didn't have a chance to take her for a drive or do much tinkering as it is 100 degrees and nearly 100% humidity here, so stay tuned! Thanks for all the help.

-Tatortot

 

[22229stingray81]

I went for another long ride today. Flap was fully open when I returned so I guess all is well with the snorkel. Didn't have the choke problem so I'm assuming the new pigtail connector fixed it. Still runs a bit rough, but I think that's mostly when it's cold. I wonder if the passenger side flap not closing fully (because of the dent in the duct) is the culprit?

It still surges a bit even when warm, but when it's cold, at a stoplight, it acts almost as if it's going to die. Not quite that bad, and it always immediately recovers. Anyways, it's better but not quite there yet. Another consumption test is on the horizon. Quick recap of what I've done:

Replaced faulty vacuum hoses
Replaced faulty EGR valve
Replaced PCV valve
Replaced leaking headlight actuator seals
Tested air snorkel operation
Replaced choke heater pigtail connector

Thanks for all the input, fellas.

-Tatortot

 

[GerryLP]

I went for another long ride today. Flap was fully open when I returned so I guess all is well with the snorkel. Didn't have the choke problem so I'm assuming the new pigtail connector fixed it. Still runs a bit rough, but I think that's mostly when it's cold. I wonder if the passenger side flap not closing fully (because of the dent in the duct) is the culprit?

It still surges a bit even when warm, but when it's cold, at a stoplight, it acts almost as if it's going to die. Not quite that bad, and it always immediately recovers. Anyways, it's better but not quite there yet. Another consumption test is on the horizon. Quick recap of what I've done:

Replaced faulty vacuum hoses
Replaced faulty EGR valve
Replaced leaking headlight actuator seals
Tested air snorkel operation
Replaced choke heater pigtail connector

Thanks for all the input, fellas.

-Tatortot

That is great news, Tattor. You have little by little fixed it to the point in which is improving.

One thing to consider, is that with all the vacuum leak fixes, the engine will likely get out of adjustment because it had been adjusted before to make up the loss of vacuum signal.

So you can check timing and idle speed, to make sure that it is running how it should. Generally speaking, the initial timing can be improved to 10 or 12 degrees BTDC, and the computer will adjust from there. Or, you can set it at the stock configuration (I believe it is 6 Deg BTDC), and then adjust the idle to the emissions' lable's specifications.

 

[22229stingray81]

Thanks, Gerry. I suppose the next thing would be to buy a timing light. Then I can start a new thread titled "how do I use a timing light?" :L


-Tatortot

 

[Antz81]

Thanks, Gerry. I suppose the next thing would be to buy a timing light. Then I can start a new thread titled "how do I use a timing light?" :L


-Tatortot

I thought timing would have been one of the first things you checked.

 

[22229stingray81]

I didn't know where to start :L

I'm still wondering if it might also be a distributor/spark problem. My records going back to 1999 are pretty extensive, and I only see the plugs were changed; nothing else on the ignition. Plug wires look good.

So next step is I'll get a timing light and we'll go from there

-Tatortot

I thought timing would have been one of the first things you checked.

 

[Tom Bryant]

Plug wires looking good don't tell you much. The original ones on our '81 looked like new yet. I replaced one a few years ago that tested bad. Last year I could not get the idle quality that I was looking for so I bit the bullet and replaced all the wires. Ironically the one wire this time that tested bad was the easiest one to replace, but I had the set so I did them all. Got a Taylor suppression set from Summit extra long so I could custom cut them to exact length and get the wire through the motor mounts. Can't do that with the ends on. I also replaced the original cap and rotor and the plugs that were fairly new, but I was already under there. I wanted to eliminate all variables. The car runs beautiful now. Routing the wires correctly is a pain but well worth the effort.

Tom

 

[22229stingray81]

Yep, I was afraid of that. Do you happen to know what the stock wires looked like? Mine are black, with red connectors.

-Tatortot

Plug wires looking good don't tell you much. The original ones on our '81 looked like new yet. I replaced one a few years ago that tested bad. Last year I could not get the idle quality that I was looking for so I bit the bullet and replaced all the wires. Ironically the one wire this time that tested bad was the easiest one to replace, but I had the set so I did them all. Got a Taylor suppression set from Summit extra long so I could custom cut them to exact length and get the wire through the motor mounts. Can't do that with the ends on. I also replaced the original cap and rotor and the plugs that were fairly new, but I was already under there. I wanted to eliminate all variables. The car runs beautiful now. Routing the wires correctly is a pain but well worth the effort.

Tom

 

[Tom Bryant]

No red boots on originals. They are a real dark grey; not quite black. They have GM numbers on them and dates. I was more worried about the engine running great than numbers for judging so I went with the Taylor in black. The repro sets with the correct numbers and dates are more expensive and I have read posts on the NCRS forum from people that said they didn't last very long. That may vary with supplier, I don't know. Taylor, MSD, Accell and even parts store sets all list under the exhaust pre-made sets that are supposed to fit like original. Like I said earlier, the problem is getting the front two on both sides through the motor mounts.There is a wire separator inside each mount that makes it impossible to force the boot between the mount and block. You could take the mounts loose from the engine and raise the engine enough to do this but that is more work than putting ends on. Besides. if you don't use each project as an excuse to buy more tools then the project has been wasted. A good plug wire crimper is something that you will be glad to have from time to time.

tom