What's the sympton of a bad AAR
Anybody sould help.
Would a bad AAR affect the functionality of a fuel pump as the pin# 12 from the 12 pin connector on relay board is connected to AAR and also to the pin# 87 of the fuel pump relay and then goes to the pin#13 of the 14 pin connector of the relay board.
Please any help?
Thanks
Full Version: Porsche
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
QUOTE(toon1 @ Nov 28 2015, 08:23 PM) 
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Are you making that up or has this happened to you?, because this is not my experience of how these components work. My D-Jet 2.0L has never ever backfired.
The AAR is a controlled air leak allowing more air into the intake only when it is cold enough outside to allow the AAR to open, then it closes as the engine warms. At the same time, the cold start valve will open allowing more fuel into the intake for the same short period of time, all to help start the engine until it reaches operating temp. More fuel and more air is not a lean condition for the engine conditions. If a backfire happened, something else was also awry.
"Cold enough" means the 10s and 20s (F) for air temps, but it just does not get that cold here in the SF bay area, so the AAR and CSV should never even come into play and could effectively be disconnected here locally. The specific temp range for the CSV is determined by the thermoswitch in the CSV circuit, values are on Brad Anders page and are dependent on which thermoswitch you have installed.
The fuel pump should not be affected by a shorted out AAR wire, but if you suspect it may be defective in some way, test its flow rate to verify its function.
I agree with Jeff. Aar will not cause a lean condition. It also will not affect performance, or cause backfiring. It will cause a non running fuel pump if the wire shorts and blows the fuse on the relay board. The aar is a very simple concept, but seems to be very misunderstood. It does not affect the way the engine runs. Period! These threads keep popping up and most of them are filled with misinformation. It supplies extra air for warm up. It has two failure modes. Stuck open(extra air even when warm) or stuck closed(no air when cold).
QUOTE(toon1 @ Nov 28 2015, 08:23 PM)
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Thank you
QUOTE(Jeff Bowlsby @ Nov 28 2015, 11:22 PM)
QUOTE(toon1 @ Nov 28 2015, 08:23 PM)
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Are you making that up or has this happened to you?, because this is not my experience of how these components work. My D-Jet 2.0L has never ever backfired.
The AAR is a controlled air leak allowing more air into the intake only when it is cold enough outside to allow the AAR to open, then it closes as the engine warms. At the same time, the cold start valve will open allowing more fuel into the intake for the same short period of time, all to help start the engine until it reaches operating temp. More fuel and more air is not a lean condition for the engine conditions. If a backfire happened, something else was also awry.
"Cold enough" means the 10s and 20s (F) for air temps, but it just does not get that cold here in the SF bay area, so the AAR and CSV should never even come into play and could effectively be disconnected here locally. The specific temp range for the CSV is determined by the thermoswitch in the CSV circuit, values are on Brad Anders page and are dependent on which thermoswitch you have installed.
The fuel pump should not be affected by a shorted out AAR wire, but if you suspect it may be defective in some way, test its flow rate to verify its function.
The AAR is just a way to get more air into the motor to make it idle faster when it is cold. In a D-Jet system a vacuum leak (the AAR is a deliberate vacuum leak) only causes the engine to speed up at idle. Like any speed density fuel injection system (my 88 Jeep pickup has one), it will NOT cause a lean running condition because the pressure feeler that is connected to the intake manifold will "see" the extra air and add fuel to compensate.
The AAR units on the 914s are 40+ years old, and are normally frozen, either in the open or closed positions. There are articles on here that will tell you how to repair them.
QUOTE(The Cabinetmaker @ Nov 29 2015, 05:22 AM)
I agree with Jeff. Aar will not cause a lean condition. It also will not affect performance, or cause backfiring. It will cause a non running fuel pump if the wire shorts and blows the fuse on the relay board. The aar is a very simple concept, but seems to be very misunderstood. It does not affect the way the engine runs. Period! These threads keep popping up and most of them are filled with misinformation. It supplies extra air for warm up. It has two failure modes. Stuck open(extra air even when warm) or stuck closed(no air when cold).
Thank you
The thing is, I tested all relays and fuses and they r all working, I don't know why I'm getting negative on the Pin #12 of the 12 connector, to the pin 87 of the fuel pump relay and the pin# 13 of the 14 pin connector, instead of positive, going to the fuel. i'm having the brown wire working as a negative and also the black and red wire as a negative instead of positive. And according to the wire schematic the pin 12 of the 12 pin connector gos to the Auxiliary Air Valve
I already looked for cracks on board and didn't find any.
Fuel pump is working, because if I power it straight from the battery, the starts right away
Thanks
QUOTE(ClayPerrine @ Nov 29 2015, 07:34 AM)
QUOTE(Jeff Bowlsby @ Nov 28 2015, 11:22 PM)
QUOTE(toon1 @ Nov 28 2015, 08:23 PM)
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Are you making that up or has this happened to you?, because this is not my experience of how these components work. My D-Jet 2.0L has never ever backfired.
The AAR is a controlled air leak allowing more air into the intake only when it is cold enough outside to allow the AAR to open, then it closes as the engine warms. At the same time, the cold start valve will open allowing more fuel into the intake for the same short period of time, all to help start the engine until it reaches operating temp. More fuel and more air is not a lean condition for the engine conditions. If a backfire happened, something else was also awry.
"Cold enough" means the 10s and 20s (F) for air temps, but it just does not get that cold here in the SF bay area, so the AAR and CSV should never even come into play and could effectively be disconnected here locally. The specific temp range for the CSV is determined by the thermoswitch in the CSV circuit, values are on Brad Anders page and are dependent on which thermoswitch you have installed.
The fuel pump should not be affected by a shorted out AAR wire, but if you suspect it may be defective in some way, test its flow rate to verify its function.
The AAR is just a way to get more air into the motor to make it idle faster when it is cold. In a D-Jet system a vacuum leak (the AAR is a deliberate vacuum leak) only causes the engine to speed up at idle. Like any speed density fuel injection system (my 88 Jeep pickup has one), it will NOT cause a lean running condition because the pressure feeler that is connected to the intake manifold will "see" the extra air and add fuel to compensate.
The AAR units on the 914s are 40+ years old, and are normally frozen, either in the open or closed positions. There are articles on here that will tell you how to repair them.
Thanks you
Thank you
The thing is, I tested all relays and fuses and they r all working, I don't know why I'm getting negative on the Pin #12 of the 12 connector, to the pin 87 of the fuel pump relay and the pin# 13 of the 14 pin connector, instead of positive, going to the fuel. i'm having the brown wire working as a negative and also the black and red wire as a negative instead of positive. And according to the wire schematic the pin 12 of the 12 pin connector gos to the Auxiliary Air Valve
I already looked for cracks on board and didn't find any.
Fuel pump is working, because if I power it straight from the battery, the starts right away
Thanks
The electrical part of the AAR has 13 ohms resistance, if I remember correctly. Somewhere between 12 and 14. That's not much resistance, so depending on how your meter is set up it may look like a short to ground.
Of course, sometimes the wire inside the AAR breaks and does short to ground.
Unplug the AAR. There's a wire that comes out of the bottom that goes into a plastic box connector. Unplug that, and make sure the end of the wire from the wiring harness can't touch ground. Then check to see if your pump works.
Double-check the fuses on the relay board; one of them powers both the AAR and the fuel pump.
--DD
Of course, sometimes the wire inside the AAR breaks and does short to ground.
Unplug the AAR. There's a wire that comes out of the bottom that goes into a plastic box connector. Unplug that, and make sure the end of the wire from the wiring harness can't touch ground. Then check to see if your pump works.
Double-check the fuses on the relay board; one of them powers both the AAR and the fuel pump.
--DD
QUOTE(Dave_Darling @ Nov 29 2015, 12:44 PM)
The electrical part of the AAR has 13 ohms resistance, if I remember correctly. Somewhere between 12 and 14. That's not much resistance, so depending on how your meter is set up it may look like a short to ground.
Of course, sometimes the wire inside the AAR breaks and does short to ground.
Unplug the AAR. There's a wire that comes out of the bottom that goes into a plastic box connector. Unplug that, and make sure the end of the wire from the wiring harness can't touch ground. Then check to see if your pump works.
Double-check the fuses on the relay board; one of them powers both the AAR and the fuel pump.
--DD
I will do that and let you k now
Thank you
Very much
QUOTE(Jeff Bowlsby @ Nov 28 2015, 09:22 PM)
QUOTE(toon1 @ Nov 28 2015, 08:23 PM)
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Are you making that up or has this happened to you?, because this is not my experience of how these components work. My D-Jet 2.0L has never ever backfired.
The AAR is a controlled air leak allowing more air into the intake only when it is cold enough outside to allow the AAR to open, then it closes as the engine warms. At the same time, the cold start valve will open allowing more fuel into the intake for the same short period of time, all to help start the engine until it reaches operating temp. More fuel and more air is not a lean condition for the engine conditions. If a backfire happened, something else was also awry.
"Cold enough" means the 10s and 20s (F) for air temps, but it just does not get that cold here in the SF bay area, so the AAR and CSV should never even come into play and could effectively be disconnected here locally. The specific temp range for the CSV is determined by the thermoswitch in the CSV circuit, values are on Brad Anders page and are dependent on which thermoswitch you have installed.
The fuel pump should not be affected by a shorted out AAR wire, but if you suspect it may be defective in some way, test its flow rate to verify its function.
I'm not making this up and YES it did happen to me, recently and in the past.
You said it yourself "controlled air leak". If it fails to operate electrically, the heat from the engine bay will eventually close it. Until it closes it will cause a LEAN condition.
last w/e my 02 sensor readings were all LEAN, by a full point, after about an hour of driving they were all back to normal. after doing some checks, guess what.
my AAR was bad.
QUOTE(toon1 @ Nov 29 2015, 10:26 PM)
QUOTE(Jeff Bowlsby @ Nov 28 2015, 09:22 PM)
QUOTE(toon1 @ Nov 28 2015, 08:23 PM)
A bad aar usually causes backfiring because a lean condition.
It has a heating element in it that heats up a metal coil that expands when hot and contracts when cold.
When cold it opens to let air bypass, when hot, no air.
When it fails it stays open letting more air in causing a lean condition and the engine will backfire.
When the engine gets hot it will close and run normally.
They usually don't cause fuel pump issues.
Are you making that up or has this happened to you?, because this is not my experience of how these components work. My D-Jet 2.0L has never ever backfired.
The AAR is a controlled air leak allowing more air into the intake only when it is cold enough outside to allow the AAR to open, then it closes as the engine warms. At the same time, the cold start valve will open allowing more fuel into the intake for the same short period of time, all to help start the engine until it reaches operating temp. More fuel and more air is not a lean condition for the engine conditions. If a backfire happened, something else was also awry.
"Cold enough" means the 10s and 20s (F) for air temps, but it just does not get that cold here in the SF bay area, so the AAR and CSV should never even come into play and could effectively be disconnected here locally. The specific temp range for the CSV is determined by the thermoswitch in the CSV circuit, values are on Brad Anders page and are dependent on which thermoswitch you have installed.
The fuel pump should not be affected by a shorted out AAR wire, but if you suspect it may be defective in some way, test its flow rate to verify its function.
I'm not making this up and YES it did happen to me, recently and in the past.
You said it yourself "controlled air leak". If it fails to operate electrically, the heat from the engine bay will eventually close it. Until it closes it will cause a LEAN condition.
last w/e my 02 sensor readings were all LEAN, by a full point, after about an hour of driving they were all back to normal. after doing some checks, guess what.
my AAR was bad.
Are we talking d-jet or l-jet?
Im not saying you didnt have a lean condition, but I wouldn't think it would be caused by a sticking AAR, at least not on a d-jet car. Its literally just an air valve, more or less the same effect that a opening the idle screw or cracking the throttle slightly would have. Any air leaks with d-jet are still metered by the system via the manifold pressure.
If it was an L-jet car and the AAR was not plumbed properly and leaking than I could see it possibly going lean/backfiring as unmetered air would be entering the system.
QUOTE(JamesM @ Nov 30 2015, 02:44 AM)
QUOTE(toon1 @ Nov 29 2015, 10:26 PM)
I'm not making this up and YES it did happen to me, recently and in the past.
You said it yourself "controlled air leak". If it fails to operate electrically, the heat from the engine bay will eventually close it. Until it closes it will cause a LEAN condition.
last w/e my 02 sensor readings were all LEAN, by a full point, after about an hour of driving they were all back to normal. after doing some checks, guess what.
my AAR was bad.
Are we talking d-jet or l-jet?
Im not saying you didnt have a lean condition, but I wouldn't think it would be caused by a sticking AAR, at least not on a d-jet car. Its literally just an air valve, more or less the same effect that a opening the idle screw or cracking the throttle slightly would have. Any air leaks with d-jet are still metered by the system via the manifold pressure.
If it was an L-jet car and the AAR was not plumbed properly and leaking than I could see it possibly going lean/backfiring as unmetered air would be entering the system.
On my old 1.7 Djet, all the AAR did was allow more air into the intake and raise the idle speed. It had nothing to do with the mixture. As James said, it's no different than opening the throttle. The FI compensates the mixture for the extra air.
Backfiring would likely be cause by an improperly adjusted deceleration valve. And a lean condition would be caused by something else, not the AAR.
I only have experience with Djet though. I have no idea what might go on with Ljet.
Jeff is correct.
D-jet woks off vaccum.
L-jet works off a different principle.
If there is any doubt open a hose on a D-jet motor or a cracked mps diaphram and the ecu will dump fuel into the engine.
D-jet woks off vaccum.
L-jet works off a different principle.
If there is any doubt open a hose on a D-jet motor or a cracked mps diaphram and the ecu will dump fuel into the engine.
So, what you are all saying is I can remove the AAR and leave the hole OPEN on the intake plenum with no worries of it affecting the system?
No......
That you can run the car without the aar. You will need to plug the hose in the intake tube so there is not an open vacuum.
You can bench test the aar to see if it is working correcrly and then see if it is if fact causing your problem.
Sounds like it is some wiring problem but trouble shooting electrical problems is a process of elimination and a great opportunity to learn about how stuff works.
My unsantimonious opinion.
That you can run the car without the aar. You will need to plug the hose in the intake tube so there is not an open vacuum.
You can bench test the aar to see if it is working correcrly and then see if it is if fact causing your problem.
Sounds like it is some wiring problem but trouble shooting electrical problems is a process of elimination and a great opportunity to learn about how stuff works.
My unsantimonious opinion.
Thanks to you all
If you by pass the AAR with a straight hose you will find the idle will race up to over 2K. Then you can pinch the hose down to reduced the air flow and you will notice the rpms dropping. I found the hose has to be pinched real tight to get it to idle near 1K.
I did this just as a test to see how the principal of the AAR worked. If you plug the hose ends or cut off all the air flow the engine will have a tough time idling when cold. It wants more air when cold.
It can be frustrating I know, I have been trying to get my L-Jet to idle properly when cold. Even with the properly working AAR mine wont idle for a few minuets on its own. The AAR can be slightly adjusted to allow a bit more air flow with the end point stop. I have mine set to allow the most air flow.
I am currently testing for air leaks and having the TB rebuilt. The TB's can become warn and cause leaks.
The most important part of the L-Jet is to get rid of any Vacuum leaks. There are many places that can cause leaks.
I did this just as a test to see how the principal of the AAR worked. If you plug the hose ends or cut off all the air flow the engine will have a tough time idling when cold. It wants more air when cold.
It can be frustrating I know, I have been trying to get my L-Jet to idle properly when cold. Even with the properly working AAR mine wont idle for a few minuets on its own. The AAR can be slightly adjusted to allow a bit more air flow with the end point stop. I have mine set to allow the most air flow.
I am currently testing for air leaks and having the TB rebuilt. The TB's can become warn and cause leaks.
The most important part of the L-Jet is to get rid of any Vacuum leaks. There are many places that can cause leaks.
QUOTE(toon1 @ Nov 30 2015, 11:34 AM)
So, what you are all saying is I can remove the AAR and leave the hole OPEN on the intake plenum with no worries of it affecting the system?
You can remove the AAR, but you will need to plug the port on the plenum that it plugs into, otherwise you'll have a vacuum leak and a high idle (which is what the AAR does when it's open). Without it you'll also need to spend a couple minutes revving your engine on a cold start until it gets warm enough to hold an idle.
I removed the AAR on my old 1.7 because it was stuck open. I gave it a 2-day soak submerged in WD-40 to free it before re-installing it. During that time, the car ran fine. Just had to warm it up like you do with carbs. All the AAR is, is a controlled vacuum leak to increase idle speed when the car is cold. The input hose comes from the intake elbow (pre throttle body) and the output hose goes to the plenum. When it's open you have a vacuum leak. When it's closed, you don't. Nothing to do with mixture because the FI compensates the mixture for the extra air that's introduced, just like when you open the throttle.
If you were running lean while the AAR was open, then you have a problem with your ECU and/or fuel delivery and not with the AAR, because the AAR is essentially a thermally controlled throttle.
FWIW I've owned my 1.7 since 1977 and it's never had the AAR, and it's not been a problem. I didn't bother finding a replacement when I did my rebuild.
I only described to the OP what happened to me TWICE.
I guess since I have a megasquirt system it's TOTALLY different....LOL
I guess since I have a megasquirt system it's TOTALLY different....LOL
QUOTE(toon1 @ Nov 30 2015, 05:48 PM)
I guess since I have a megasquirt system it's TOTALLY different....LOL
Yeah...you probably should've mentioned that
QUOTE(toon1 @ Nov 29 2015, 09:26 PM)
my AAR was bad.
There was likely something else that was going on... In a properly set up injection system (L-jet or D-jet!) the AAR should not affect the mixture. At all. The air going through the AAR is metered air; L-jet takes the air from downstream of the air flow meter, while the D-jet MPS sees the higher pressure of air getting in. In your case, there may have been something else going on.
--DD
QUOTE(pete000 @ Nov 30 2015, 09:15 AM)
If you by pass the AAR with a straight hose you will find the idle will race up to over 2K. Then you can pinch the hose down to reduced the air flow and you will notice the rpms dropping. I found the hose has to be pinched real tight to get it to idle near 1K.
I did this just as a test to see how the principal of the AAR worked. If you plug the hose ends or cut off all the air flow the engine will have a tough time idling when cold. It wants more air when cold.
It can be frustrating I know, I have been trying to get my L-Jet to idle properly when cold. Even with the properly working AAR mine wont idle for a few minuets on its own. The AAR can be slightly adjusted to allow a bit more air flow with the end point stop. I have mine set to allow the most air flow.
I am currently testing for air leaks and having the TB rebuilt. The TB's can become warn and cause leaks.
The most important part of the L-Jet is to get rid of any Vacuum leaks. There are many places that can cause leaks.
Thank you Pete
The Army has warped my brain and I keep thinking AAR means After Action Review...
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.