AEM Gauge shows lean at WOT. Wondering why?
 

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:

http://forums.pelicanparts.com/porsche-911-technical-forum/1041464-cold-start-issue.html

Thanks,

Lou

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

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.

Here is some pics:

http://forums.pelicanparts.com/uploa...1574645441.jpg

http://forums.pelicanparts.com/uploa...1574645441.jpg

Since its a 78 it doesnt have the Lamba System.

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.

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

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.

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

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.

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.

CIS Troubleshooting.........
 

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

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.

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

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....

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

Unit of measurement clarification..........
 

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

Tony,

My mistake 18 inch hg.

Lou

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.

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

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

Juanbeane: Bursch cat test pipe. Sensor is in bung in picture.http://forums.pelicanparts.com/uploa...1579480133.jpg

When checking fuel pressure have you dead headed the pump to see how quickly it goes to 7 Bar? I think it's 7 Bar anyway, It's been a couple years.
I had a similar issue with a bad pump. The car ran and drove fine. After installing headers, bigger turbo and other mods the car would lean out bad on boost. A AFR gauge went in with the mods. When setting the adjustable WUR I did dead head the pump, as suggested, and it lazily got to like 6 or 7 bar and thought that everything was ok.
Found out with some tests the front pump was not pumping enough volume.
Installed the new front pump and checked pressures again. This time when I closed the valve and dead headed the pump the gauge snapped to full pressure. Problem solved.

So dead head the pump while the gauge is attached and see how fast it hits max pressure. It should be instant. If it slowly raises then you have a weak fuel pump that can't keep up.

Derrick

Thanks for the reply. Can you explain the steps to dead head the pump? Is it the same as the system pressure test, but keeping an eye on how fast it climbs?

Lou

Misconception.........
 

Derrick,

You can not compare a 930 CIS with two- FP with a normally aspirated CIS with a single fuel pump. These are two distinctly different CIS engines. The tests and parameters are night and day difference. Your 930 has a system fuel pressure between 90~100 psi. while Lou’s is only 65~75 psi. FYI.

Tony

Yes, When you close the return valve during the pressure test the gauge should snap to full pressure. If it climbs slowly the pump is weak.
Fuel filter could be clogged too.

The pressure should still climb rapidly to max pressure. A weak pump or clogged filter in any fuel system will cause a lean condition at full throttle.

May be a dumb question but what did the cat test pipe replace? I only ask because the PO for my car did some creative emissions changes that tied a cat, which is not standard on a euro car or your year, to the wur return fuel line. When that plumbing was disconnected, I had no enrichment. Have you owned the car throughout? Seems very strange the leaning shows up after all the engine work you have completed.

So the cat bypass pipe replaced the original catalytic converter. I have owned the car for about 5 years but never did I have an AFR gauge tied to it. It could of been doing this prior to the rebuild but I wouldn't have known. Today I pulled the CIS boot to do a thorough smoke test with a smoke machine I built. Hopefully something will show up. I will keep you guys posted.

http://forums.pelicanparts.com/uploa...1579576490.jpg

My mistake. I thought the cat started in 1980 but that was when they added Lambda and a better cat. Hopefully the smoke machine will find something.

Is it possible the decel valve is bad? I thought I read it closes off vacuum at specific points. If it is allowing some vacuum through in the wot range, the wur will not fully richen with pressure staying up a bit. You tested vacuum to the wur for cold start. Maybe testing the decel ports is in order.

How does the car feel at WOT?
if the AEM gauge is correct, then WOT should feel really slow when AFR's are above 14...the car should feel like 100hp instead of 200hp. I have driven my 3.0L SC with bad CIS system, and AFR's not rich enough (14, 15), and it feels completely flat. It feels broken. A healthy SC should have a lively acceleration, building power from 2000, becoming very nice at 3500rpm, and still crescendo to about 5000 rpm and then plateau/taper off.

just trying to exclude the AFR readings from the investigation.

If AFR numbers are correct, and the car does indeed feel slow, you have a problem with fuel delivery i think. Injectors were cleaned, so we maybe can exclude those...WUR is fine too. Then we have fuel pump and fuel distributor as main suspects? Has the car been sitting for a while before you got it?

Conducted the smoke test today using Tony's method and noticed a hairline crack on the seam of the airbox near the number one intake pipe. A small amount of smoke was seen coming out of this area and it definitely would not have been found by just visible inspection. Everything else was good. Since it is reachable I decided to seal it up with some JB weld. I'll give an update tomorrow. Hopefully this is it and the JB weld works.

http://forums.pelicanparts.com/uploa...1579663722.jpg

Wreckah: car does feel strong at WOT. Not sluggish at all but I do believe it could be better. We will see how it is tomorrow

CIS troubleshooting.......
 

You have to verify and confirm the absence of significant source/s of unmetered air. Not being able to find one does not mean you don’t have any. A pressure test with a smoke generator will tell you if the system is free of air leak source/s or not.

People have been using AFR (air to fuel ratio) meter blindly. The tool is very efficient and reliable if used correctly.

Tony

After adjusting the mixture, .. didn't you forget to pull the allen wrench again out of the FP?
This sometimes even happens to mechanics with 30 years of 911 experience :-)
Cause then the Air sensor plate can't move freely upwards and the plug in the FD won't reach the position where enough fuel will be provided at WOT.

I always took the Allen key out after each adjustment.

So, I sealed up the hairline cracks alongside the airbox. Re checked with smoke and all seemed good. Lean condition at WOT is still present as well as rough cold start. Did replace the AEM Gauge with another one provided by the company, still same lean numbers at WOT. Whats your thoughts on what to do next? Here are mine:

1. Conduct a fuel test putting the injectors in the bottles to check for even fuel flow and pattern. (They were cleaned by Mr. Injector after the rebuild)
2. Replace fuel filter. But this should be good because system fuel pressure was in spec, right?

At this point, I think its a fuel issue since there are no present vacuum leaks, cold and warm pressures are in spec, WUR was rebuilt, new spark plugs, cap, rotor, and wires.

What am I missing? Thanks

Lou

Any chance you can video the gauge as you run it a bit at wot?

Today I got a chance to test the injectors. I placed them in baby bottles, bypassed the relay, and lifted up the air flow sensor plate. Each injector had a good spray pattern, no leaks, and consistent volume across all six. I'm going to check the decel valve tomorrow. Im also going to disconnect the vacuum line to the WUR, tie that line into my vacuum gauge which I will monitor from inside the car (long vacuum hose) and go do some WOT pulls to see if the vacuum drops off.

http://forums.pelicanparts.com/uploa...1580010311.jpg

I believe you're missing EFI :D

LOL. CIS has me losing my mind.