AEM Gauge shows lean at WOT. Wondering why?

[1987 Porsche]

So I just installed my AEM gauge in my 78 911. I adjusted the warm idle mixture to 13.5 and have my idle set at 950. During wide open throttle or hard acceleration I notice the gauge climbing to the 15's indicating the car is leaning out rather then getting richer. Why would this happen?

Recent engine rebuild with 9:3:1 later SC pistons, 964 cams, bursh bypass pipe. This AEM Gauge install all stems from a cold start issue which I am still struggling with:

Cold Start Issue

Thanks,

Lou

[Reiver]

What controls enrichment on the US models? The Lambda? Is the lambda still there or gone?
I have a Euro SC and the WUR controls ours/mine...at WOT , also with an AEM, I see in the 11's....I'm also set about 13.5 ish as the 9.8-1 likes richer not poorer....

Whatever enrichment system you have it isn't reacting... I suspect you know that...I posted to let you know what you should see when set at 13.5...good luck

[SkiVT]

Double check the vacuum lines path all the way to throttle body from this pic

911 CIS Primer - Vacuum Lines

Post additional pics of all your lines also might help us help you.

[1987 Porsche]

Here is some pics:





Since its a 78 it doesnt have the Lamba System.

[timmy2]

Reiver,
The 78 and 79 US models are the same as the later Euro cars without Lambda.
All enrichment is via the WUR (aka system pressure regulator).
When I had CIS, my wideband gauge would drop into the 11’s at WOT.
Throw a fuel pressure gauge on and check your WUR and system readings are to spec.

[timmy2]

Just read your other thread.
Unmetered air is what I would be searching for. (Vacuum leak)

[SkiVT]

Lou

When I go back and read the other thread I am seeing a ccp of 1.7 w/o vacuum and 2.0 with vacuum. You also stated that you do not observe a jump in pressure when the TTV opens. I thought the normal pressure difference between vacuum and no vac is .6 or .7. Did you actually run the car at wot with the loner wur from Tony? I am simply wondering if your wur isnt reacting enough to vacuum. The wcp doesnt really support this thought but I cant figure out how vacuum can be working and you not see a change when the TTV opens. If there is no change at that early cold stage then the wot behavior shouldnt be surprising. We are just stumbling to identify exactly why...

Certainly should check pov etc for air leaks but I thought you smoke tested it all recently.

[1987 Porsche]

Mike,

I did not run a WOT test with Tony's WUR. I did not have the AEM gauge at the time. I am anxious to see if his WUR would perform differently now that I can monitor the air fuel mixture while driving. Once again I am going to look for vacuum leaks that I may have missed.

Thanks

[SkiVT]

BTW: your vac lines look like there are connected correctly. So assuming no clog in any of those lines, you should have vacuum. I am not sure if it's possible for the amount of that vacuum to be below "spec" so someone may be able to answer that question. I think of it like this: your wur has two distinct pressure curves, one w/vac and one without vac. You documented those using the minivac but using the minivac is not always the same as relying on the engine for that same vac level. Vacuum lets the engine dance between the two curves based on throttle input, after the TTV is open. Before the ttv is open, you are on the w/o vacuum curve for a short amt of time. You seem to be seeing no effect of vacuum both during the TTV closed time and at WOT.

In addition to using the AEM gauge, I might also try starting the engine cold with your pressure gauges attached to see if TTV close/open impacts Tony's wur with increased pressure. Seeing the pressure drop at WOT would also be nice but harder to do and observing your AEM should be just as good.

[Reiver]

Originally Posted by timmy2

Reiver,
The 78 and 79 US models are the same as the later Euro cars without Lambda.
All enrichment is via the WUR (aka system pressure regulator).
When I had CIS, my wideband gauge would drop into the 11’s at WOT.
Throw a fuel pressure gauge on and check your WUR and system readings are to spec.

That is exactly how my Euro acted before getting the WUR rebuilt by Larry at CIS Flowtech…. ran great but on hard accel/WOT leaned out....I suspect a WUR issue.

[boyt911sc]

Lou,

Install a vacuum gauge between the WUR and TTV and run the motor. The initial 20 sec. should give you no vacuum reading until the TTV opens up. The WUR will register a CCP (without vac. followed by with vac.). The WCP should have two values (with & w/o vac.). And lastly, a pressure test or a smoke generator will confirm the presence of unmetered air if any.

I loaned you a rebuilt and calibrated WUR to test in your motor. The problem was still present. The culprit is NOT caused by a WUR. It is something else you have to look and identify. Keep us posted.

Tony

[1987 Porsche]

I was out there today messing around with the car and decided to plug the hose that runs to the side of the WUR just to see what would happen. The AEM gauge showed a richer condition 13.1. It was around 14.1 when hose is tied to the side of WUR. The car idled a lot smoother and felt alot quicker with that vacuum line pluged. It still leaned out at WOT to around mid 14's.

Tony, I will go ahead and try the vacuum gauge test and will post results. As far as using your WUR I did not have the AEM gauge at the time when you loaned me yours. I am wondering if I borrowed it again if it would show a Rich condition at WOT.

Reiver, I am also suspect of the WUR not functioning properly when throttle is applied. I suspect the cold start issue and WOT lean condition maybe two separate issues. Just a guess.

[pampadori]

Ensure that you don't have any exhaust leaks before the sensor.
https://www.hotrod.com/articles/exhaust-leak-affects-widebando2-sensor-readings/

[Reiver]

Originally Posted by 1987 Porsche

I was out there today messing around with the car and decided to plug the hose that runs to the side of the WUR just to see what would happen. The AEM gauge showed a richer condition 13.1. It was around 14.1 when hose is tied to the side of WUR. The car idled a lot smoother and felt alot quicker with that vacuum line pluged. It still leaned out at WOT to around mid 14's.

Tony, I will go ahead and try the vacuum gauge test and will post results. As far as using your WUR I did not have the AEM gauge at the time when you loaned me yours. I am wondering if I borrowed it again if it would show a Rich condition at WOT.

Reiver, I am also suspect of the WUR not functioning properly when throttle is applied. I suspect the cold start issue and WOT lean condition maybe two separate issues. Just a guess.

Check the lines for leaks but not all 'rebuilt' WUR's are the same....there is only one Bosch authorized WUR repair in the US that can get ALL of the internal parts and I mentioned the outfit in my other post....

[1987 Porsche]

Tony,

I went ahead and hooked up a vacuum gauge to the line from the ttv to WUR. Like you said the first 20 seconds there is no vacuum reading then all of a sudden I do get 18 mmhg of vacuum indicating the TTV is functioning as it should.

Lou

[boyt911sc]

Originally Posted by 1987 Porsche

Tony,

I went ahead and hooked up a vacuum gauge to the line from the ttv to WUR. Like you said the first 20 seconds there is no vacuum reading then all of a sudden I do get 18 mm hg of vacuum indicating the TTV is functioning as it should.

Lou

Lou,

Please double check your pressure gauge dial. What is the unit of measurement indicated on the face of the gauge? The unit could be inch Hg vac and not mm Hg. Keep us posted. Thanks.

Tony

[1987 Porsche]

Tony,

My mistake 18 inch hg.

Lou

[tdw28210]

Total shot in the dark here, but I have read that some of the early replacement fuel injectors would run lean at WOT. Specifically the ones originally made for Jaguars that were also used as replacements for the 911s.

[1987 Porsche]

Wanted to give an update to this post. So I sent Tony (BoyT911sc) my WUR for testing and evaluation. Tony decided that it needed to be rebuilt and recently sent it back to me. He set the Cold control fuel pressure to 2 bar. Warm control fuel pressure 2.8 bar without vacuum and 3.5 bar with vacuum. So now we definitely know the WUR is good. Lean issue at WOT is still present. My question now is when I step hard on the gas the AEM gauge starts to go lean, but as soon as I come off the gas the AEM Gauge goes rich to around 11 or 12 AFR. This is opposite of what it should be doing, why would this be happening? Any other advice is appreciated.

Thanks

Lou

[juanbenae]

I did not read the other thread, but what exhaust are you running and where is the AF sensor bung?