AEM Gauge shows lean at WOT. Wondering why? - Page 3

1987 Porsche · 1987 Porsche's Garage

A thought just came to mind. When I did the injector test on the initial turn of the key with relay bypassed each injector did shoot a little gas into the baby bottles when the system pressurized. Why would this happen? I did not touch the air sensor plate. I read a post that said "when checking with CIS they will drip with fuel pressure if the mixture is set too rich, but all 6 should drip." Is this true?

Thanks

1987 Porsche · 1987 Porsche's Garage

Yesterday went ahead and hooked up a vacuum gauge with a T connector from Thermo Time Valve hose to WUR. I had the vacuum gauge in the car and was able to monitor the vacuum at WOT and it definitely showed a vacuum drop at WOT. It is doing what it should.

Today went out there and conducted a Fuel Delivery Volume Test. I disconnected the bottom fuel line at the Accumulator and placed this line in a gallon milk jug. Then bypassed the relay, my dad turned the ignition to on while I timed the flow rate for 30 seconds. This is where it gets interesting. The volume after the 30 seconds was less than half what the fuel delivery minimum should be (1.06 qts in 30 seconds). I conducted this test twice and same results. Again less than half what it should be. From what I can gather is this could be causing my lean condition at WOT because the volume of fuel is not there. It is starving for fuel when the pedal goes to the floor. Your thoughts?

My next test is to check fuel delivery volume at the pump to confirm there is not a blockage in the line from fuel pump to accumulator. Once confirmed, then possibly check the fuel filter inside the tank. According to the records that were given with the car this could be the original fuel pump.

Lou

1987 Porsche · 1987 Porsche's Garage

This is all I got:

The black line below shows with water the amount of fuel I got after 30 seconds. When it should fill that whole quart bottle up. Less than half of what it should be.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by 1987 Porsche

Yesterday went ahead and hooked up a vacuum gauge with a T connector from Thermo Time Valve hose to WUR. I had the vacuum gauge in the car and was able to monitor the vacuum at WOT and it definitely showed a vacuum drop at WOT. It is doing what it should.

Today went out there and conducted a Fuel Delivery Volume Test. I disconnected the bottom fuel line at the Accumulator and placed this line in a gallon milk jug. Then bypassed the relay, my dad turned the ignition to on while I timed the flow rate for 30 seconds. This is where it gets interesting. The volume after the 30 seconds was less than half what the fuel delivery minimum should be (1.06 qts in 30 seconds). I conducted this test twice and same results. Again less than half what it should be. From what I can gather is this could be causing my lean condition at WOT because the volume of fuel is not there. It is starving for fuel when the pedal goes to the floor. Your thoughts?

My next test is to check fuel delivery volume at the pump to confirm there is not a blockage in the line from fuel pump to accumulator. Once confirmed, then possibly check the fuel filter inside the tank. According to the records that were given with the car this could be the original fuel pump.

Lou

Lou,

You were measuring the FP flow rate at the wrong location. Either do it before the fuel accumulator or at the return line. You are not getting all the fuel return at the fuel accumulator drain line. Some are flowing back to the gas tank.

Repeat the test using these locations:
a). Disconnect the delivery fuel line to the fuel accumulator.
b). Disconnect the main return line at the engine bay near intake #3.

Both measurements should give you the same flow rate. Keep us posted.

Tony

1987 Porsche · 1987 Porsche's Garage

Tony,

I disconnected here:

Is this wrong? This is the spot I saw in the books picture, bottom of the fuel accumulator.

boyt911sc · boyt911sc's Garage

Lou,

The fuel line from the bottom of the fuel accumulator is part of the return line. This line connects to the main fuel return line. Reconnect the bottom fitting of the FA and measure the flow rate at the main return line going to the gas tank. There is a fitting mounted to intake runner #3.

A more convenient location to do the test is at the main delivery line before the fuel accumulator. Why are you measuring at the bottom of the fuel accumulator? Where did you get this procedure? Keep us posted.

Tony

1987 Porsche · 1987 Porsche's Garage

I got it from the Bentley service manual. Here is what it shows:

boyt911sc · boyt911sc's Garage

Lou,

The return fuel line from the fuel distributor for your engine goes near intake runner#3. And that is where the fuel accumulator return line connects to the main return line to form a tee joint. Any flow you were getting from the disconnected line from the bottom of the fuel line is only partial and the rest goes to the other line.

Not everything you read is CORRECT. Bentley SC Manual is a very good reference maintenance manual and I have one too but has several errors. Sometimes you need to use common sense and not just follow blindly. I committed a lot of mistakes and learned from it.

Tony

1987 Porsche · 1987 Porsche's Garage

Ok so you are saying here:

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by 1987 Porsche

Ok so you are saying here:

Lou,

To test your FP, the most logical location would be at the FP exit hose. But that will entail removing the skip plate and raising the car. Several feet away from the FP is the connection to the fuel accumulator. This is a very convenient location to do the tests for flow rate, residual pressure, and FP check valve. Use this location for your next tests.

The connection I am suggesting is located on top of the fuel accumulator with a hook metal fuel line. Not the one you are showing in the picture. Hope I am making it clear enough to be understood. Keep us posted.

Tony

1987 Porsche · 1987 Porsche's Garage

Ok will do. The car is already on the lift and that was the test for tomorrow. Thanks

Lou

boyt911sc · boyt911sc's Garage

Lou,

It is not your fault. The procedure suggested in the Bentley Manual is rather STUPID. Why? Because the amount of fuel you could collect from disconnected fuel line from the bottom of the fuel accumulator will be only a partial of the total return line delivery volume.

As you have demonstrated in your tests, the missing volume is going back to the gas tank.

Tony

1987 Porsche · 1987 Porsche's Garage

I conducted some more test today, at the fuel pump and at the return line that Tony mentioned near the number three intake. The fuel pump put out 2.5 liters in 30 seconds and the return line at the intake put out 2 liters in 30 seconds. Fuel pump number is Bosch 0580254984. Thoughts?

Lou

1987 Porsche · 1987 Porsche's Garage

According to this, I guess the pump is good.

SkiVT · SkiVT's Garage

Although it would seem next to impossible after all the rebuild activity and testing you have done, I have my nickle on unmetered air (yet to be found) as the culprit. It seems like the simplest possible reason that appears as both a cold running and lean WOT issues. You can shoot me later if you find a more complicated source of the problem......

1987 Porsche · 1987 Porsche's Garage

Wanted to post some videos and see everyone's thoughts. Tony recalibrated the WUR and now I'm running a WCP w/vacuum at 50 psi and WCP w/o vacuum at 39 psi, 11psi difference. Idle AFR at this point is set at 12.7 at 1000rpms. WOT only is coming down to a 13.2 AFR.

THIS video shows the pressure drop with rebuilt WUR:
https://youtu.be/eLvZpy2W0sY

This video shows the AFR gauge at WOT pass. At the time of this video I did not have a rebuilt WUR and the idle AFR was set at 13.5. You will see WOT AFR only goes to 13.8. Like I said before now I'm getting 13.2 WOT pass with a 12.7 AFR at idle recalibrated WUR.

https://youtu.be/IfTtZt1mRaI

Do you think this 78 non lambda should still be getting a lower AFR. Vacuum checks were once again conducted an all good.

Thanks,

Lou

1987 Porsche · 1987 Porsche's Garage

Just wanted to finish out this post. Thanks to Tony recalibration of the WUR (WCP with vacuum 50psi and without vacuum 39psi) and a little timing advance (32 degrees at full advance, about 6-7 degrees at idle) I was able to see high 12s on the air fuel gauge at WOT. Idle MIxture is set at 13.3. Still working on a cold start issue, but hopefully will resolve it soon.

Thanks for everyone's help. Stay safe.

Lou

911pcars · 04-01-2020, 09:27 AM

Quote:

Originally Posted by 1987 Porsche

Juanbeane: Bursch cat test pipe. Sensor is in bung in picture.

Not necessarily related to your symptoms, but the location of the O2 bung isn’t ideal. It should be relocated further downstream so it’s more exposed to the exhaust flow from both cylinder banks.

Sherwood

1987 Porsche · 1987 Porsche's Garage

I totally understand what you're saying and the thought did cross my mind to move it. But hopefully I'll get some SSI's soon and wont have to move it

911pcars · 04-01-2020, 11:34 AM

Quote:

Originally Posted by 1987 Porsche

I totally understand what you're saying and the thought did cross my mind to move it. But hopefully I'll get some SSI's soon and wont have to move it

Yes..... but, unless a dual WB sensor system is employed, the SSI HEs splits the exhaust system before reaching the muffler.

S