Rebuilt Rochester E4ME on a 1981 Corvette Code 45 Running Rich on Highway

[Reaper19]

Hi everyone,

I have been trying to track down how I can stop my CEL from coming on at highway speeds producing a code 45 (running rich condition) in the ECM on my 1981 corvette. I had my motor and carb rebuilt and since I have been able to adjust the carb to idle decent, but it runs rich only at highway speeds. The motor is mostly rebuilt stock, little bigger pistons and cam, 882 heads (original 624's were cracked) but nothing outrageous and is well withing the factory specs for the ECM according to the engine builder.

Items I have completed:
- replaced O2 sensor
- replaced all vacuum lines
- checked for vacuum leaks and found none
- found the EVAP can was clogged and charcoal packed solid. I was able to break up the charcoal by shaking and re-installing. Since, the gas smell in garage has gone away. I have also ordered a replacement and will be delivered next week.
- I also found a leak in catalytic converter so I ordered a new Magnaflow high flow which will also be here next week
-I have checked carb with Dwell and got it between 25-35 at idle
- Adjusted IAB
- idle screws are both 3 1/3 turns out now

Anyone have a suggestion why I may only be getting a rich condition at highway speeds?

Thanks

Reaper19

[429bbf]

there is an excellent discussion on may 08-2014 . use the search and type in E4ME look at the discussion by members (peer81 and jjr this may answer some of your questions .hth

[Cliff Ruggles]

Light throttle cruise A/F is controlled by the M/C solenoid.  It may not be working correctly, or not adjusted correctly.  There are two adjustments which control this area of the carburetor, the height of the M/C solenoid, and the upper metering rod limit adjustment.

If you are certain the solenoid is working, look at adjusting it and the maximum height of the metering rods.....Cliff

[Reaper19]

Thanks Cliff. I am certain the M/C is working, when I first had the carburetor rebuilt locally at a National Carb shop, it was running rich always and did not run smooth at all and I had a hard time starting when warm no matter how I adjusted the IAB or mixture screws. Afterwards I took it back and they found the newly replaced M/C was dead. They replaced it and I am able to set the dwell at idle to ~28 with the two mixture screws out 3 3/4 and IAB adjustments. I can also hear the M/C clicking away. When I take the car for a test run and then test with dwell I can see it bouncing around 54 which should mean it is calling for a lean mixture. If I slow down from highway speeds the CEL goes off and no more rich condition. I just replaced the emissions evaporator can, new Bosch O2 sensor and a Magnaflow catalytic converter. Took it for a ride without resetting the computer and still ended up with a CEL code 45 rich condition. Puzzling.

When you say adjust the solenoid are you referring to the rich and lean stops?

Thanks

Randy

[Cliff Ruggles]

There are two adjustments, the actual height of the M/C solenoid, which is the first hole closest to the front of the carburetor. 

There is a second adjustment for the upper limit or height the metering rods can reach, it is below the hole right in front of the upper idle airbleed adjustment.

When we build those carburetors here, we tap those holes and install set screws, then slot the adjustment screws with a fine hacksaw blade so the tuner can make adjustments without taking the carb apart.

There could be other issues not related to adjustments, more related to the quality of the rebuild parts, float out of adjustment, wrong N/S assembly, left the spring off the M/C solenoid, worn parts, incorrect parts, "generic" calibration,  etc......Cliff

[Reaper19]

I went out and bought a vacuum gauge today to help set the carb mixture screws and IAB along with using the dwell meter. I also brought the idle down to what the under the hood label and manual recommend, it is now set to 500-550 RPM while in drive, before it was around 650-700. The timing is set at 12 degrees BTDC, factory is 6 but my other corvette club members and gear heads are recommending 10-14 for best performance, do you agree?

The vacuum is sitting right at 18 1/2 now. The high end was 19 and 18 1/2 looks to be the sweet spot with the most stabile needle. Afterwards I readjusted the IAB to further stabilize the vacuum and allow the engine to run as smooth as possible. Ran the engine at 1800 RPM for a minute or so to get it in a closed loop, watched the dwell go up to 53 and then settled in at 31.5 at idle. This was the first time I was able to achieve a dwell close to 30, stable and hunting a half point up and down. Took the car out for a test drive and what a difference when accelerating from a stop or WOT, no hesitation at all and very responsive. But I still get a CEL at 50MPH or higher cruising speed and code 45, rich condition.

Next steps will be counting the numbers of turns to bottom out the lean stop and then back it out again to the same point for reference since it had to be removed by the carb rebuilder to install a new M/C and I am not sure if he placed it back in the same spot. The rich stop appears to be set at the factory setting since the plug is still installed. I also checked the space between the M/C rich and lean stop and it is right around 3/32, the setting recommended in the shop manual. I plan on turn the lean stop in a 1/4 turn at a time and test drive to see if that corrects the rich condition.

[Cliff Ruggles]

I'd go back into the carb and check float height, and see if they even put the correct N/S assembly in it, most likely not. 

Fuel level is a big player with fuel delivery, and effects the calibration more than most folks think.

I would also set up the M/C solenoid and metering rod limit screw to be fully adjustable without taking the carb apart, then you can fine tune it to get it within "range" after it is verified that everything else is correct.

I'd also recommend installing our kit while it's apart, far superior parts than what they would have used in it.  Our pump has best seal on it in this industry, it is NOT the same as the blue seals others are using, and our pump comes with custom wound springs for increased efficiency and performance........Cliff

[Reaper19]

Thanks again Cliff. I am waiting for the car to come back from the engine rebuilder for its 500 mile checkup, oil change, check torque on bolts etc. Once I get it back I am going to try a few more electrical checks, float level and M/C lean adjustment height, and possibly change out the ECM if necessary. If all still points to carb and I have issues with the carb I am going to give the local carb rebuilder one more chance and if he cannot dial it in ask for a refund and purchase one of your kits. I checked out the carb number (17085204) and it is the proper model used by GM on multiple cars from 81-90.

Thanks

Randy

[Cliff Ruggles]

It's probably unrelated to the rich running condition (but could be a "player"), but SBC 882 heads are complete "door stops".  They are the WORST heads to ever sit on a 350 engine that left the factory.  Very poor flowing, and super-restrictive on the exhaust side.  This was done for emissions most likely, to hold back exhaust flow to lengthen burn time and/or more time for the CAT to do it's work.  Not sure about any of that, but we NEVER use those heads for any power level or type of SBC engine build.

624's were a tad better, but every set I've ever seen was cracked as they are paper thin.  I'd put a set of World Products heads on my wish list, or even a set of factory 441, 336, 487 or 993 castings would be a HUGE upgrade from where you are at now.......Cliff

[Reaper19]

Hi Cliff,

Just an update, I talked to the carb re-builder again the other day and told him I am still having the same issues. He said he would rebuild one for me that was never touched and this would be the first time it was rebuilt. He asked for the series number on the carb I had, come to find out I had 17085202 that the previous owner put on the 1981 corvette which is actually from a 85 Monte Carlo SS or Trans AM H. O. So I looked up the carb that should have come on my 81 vette and it was 17081228. So he found one that was never rebuilt before. I put it on the car and so far the rich condition is gone   :-) after taking a pretty good test drive. I installed it on the car along with a new stainless steel fuel pump-to-carb line. The only item I will need to address is readjusting the TPS to correct the lockup on my tranny after adjusting the idle. They installed all the plugs this time so I will need to drill out the TPS plug for adjustment.

Do you sell the replacement plugs only for the TPS, Lean and Rich adjustments or have a good idea what I can use to plug the TPS adjusting hole back up?

Thanks again, Randy

[Reaper19]

Carburetor dialed in finally. I could not get the idle running right or dwell dialed in unless the IAB was only 1 turn out. I took the IAB all the way out and found when this carburetor was built the bottom o-ring must have fell off and was at the bottom of the opening. Being the weekend I found a replacement at the hardware store, installed and now I am able to set everything, dwell at 30 degrees, idle mixture screws 3 1/3 turns out, TPS at .56, timing 12 BTDC and idle 600 in drive. Factory idle is 500 but with the new cam it likes 600 better.

The problem I now have is a rough or off idle and the motor shakes a little, not a smooth idle. Any ideas?

[Cliff Ruggles]

I have the correct "O" rings for the valve in stock, and would put the correct ones on it.

The upper IAB adjustment allows the tuner to have full control of fuel at idle speed, when the carb is set up correctly.

If there is a vacuum leak someplace, or throttle plates not indexed/sealed up, or a leak at the primary shaft, getting a smooth idle may not be possible......Cliff

[Reaper19]

Thanks Cliff, I ended up taking the carb back to the rebuilder. The TPS was bad and replaced, new O-rings installed and lubed. I am able to get the dwell set up correctly but it still has a little off stumble/rough/surge at idle, otherwise the
engine is performing better than ever. I am able to smooth it out by changing the factory suggested idle from 500 to ~650 or more while in drive. I did have a little bigger cam and higher compression pistons installed when the engine was rebuilt, might be the reason it wants more idle RPM. Also, I have timing set at 12 BTDC. I checked all vacuum lines found that the cruise transducer was leaking so I plugged that line for now. I capped all vacuum ports one at a time and no change, except when I remove the map sensor vacuum line, the car really runs rough if unplugged.