Questions about AFPR

[oldman]

Vacuum is near 18-22 at idle (right before it cuts off) fuel pressure is at 37psi when the car is running and it raises like a champ when boost is seen.

Then the FTS isn't doing its job, your fuel pressure should be at about 37psi - 10psi (-20inHg) = 27psi, where is the vacuum line to the FTS coming from?

At first I thought it was just a boost leak so I tested then I disconnected the fuel pressure solenoid to eliminate a possible boost/vac leak there as well.

How much pressure and for how long did the intake tract hold? Idle rpm? 18-22 inHg is a big variation, do you have idle surge? Have you check your logger to make sure TPS is set correctly and ISC is functioning properly?

 

[RiceKiller_TSi]

Then the FTS isn't doing its job, your fuel pressure should be at about 37psi - 10psi (-20inHg) = 27psi, where is the vacuum line to the FTS coming from?

The vacuum line for the FTS is coming directly off the intake manifold nipple midway between the injectors. I basically unplugged it from the fp solenoid and went directly to the FTS with it. I think the FTS is working correctly because both my guages reflect the changes in the fuel pressure, the one on the FTS and the one on the fuel filter. Also when boost was applied it raised the pressure in response.

How much pressure and for how long did the intake tract hold? Idle rpm? 18-22 inHg is a big variation, do you have idle surge? Have you check your logger to make sure TPS is set correctly and ISC is functioning properly?

Well its hard to tell what the vacuum is being I can't keep the rpms stable enough which is the reason for the variation. I MAY have idle surge. I havent checked the ISC lately. I just read a thread that points to this as well. http://dmtalon.v8eaters.com/ISC.html I'm going to see if its dead when I get home tonite. Would this cause my car to have the aformentioned symptoms?

My intake tract doesn't hold the boost at all. I don't know if you remember but it seems to leak out into the engine somewhere. I can hear it when I take off the oil filler cap. It will leak out really slow but I've driven it like this and it didn't seem to affect power much, let alone make it stall. What you thinking?

The TPS is working correctly as verified by my logger. It hits 99.6% when I floor it. Thanks for all your help. You are an invaluable DSM resource and not just another mod.

 

[oldman]

The vacuum line for the FTS is coming directly off the intake manifold nipple midway between the injectors. I basically unplugged it from the fp solenoid and went directly to the FTS with it. I think the FTS is working correctly because both my guages reflect the changes in the fuel pressure, the one on the FTS and the one on the fuel filter. Also when boost was applied it raised the pressure in response.

But that doesn't explain why you're idling at 37psi instead of 27psi, unless you mis-typed in one of your previous post, the AFPR isn't doing its job or you have return line/tank pressure issues.

My intake tract doesn't hold the boost at all. I don't know if you remember but it seems to leak out into the engine somewhere. I can hear it when I take off the oil filler cap. It will leak out really slow but I've driven it like this and it didn't seem to affect power much, let alone make it stall. What you thinking?

This is what I would do.

1. Make sure your gas tank is properly vented. Bottom line, your fuel pressure has to be at 27psi.

2. Check your plugs and wires.

3. Re-visit the leak test and this time start from the TB elbow so you can focus on vacuum leaks, I'm sure you're familiar with the 20psi for 30 seconds........etc. If you hear pressure leak in the crankcase let's find out why.

4. After you have fixed all leaks and able to pressurize the intake up to 20psi, adjust your TPS to around 10% at idle.

5. Properly adjust the BISS and set your idle at around 750, post back if you're not able to achieve this.

6. Check and make sure, adjust if need be, the ignition timing is at 5* BTDC.

Post back if problem persists, at least this will eliminate alot of possibilities.

 

[RiceKiller_TSi]

But that doesn't explain why you're idling at 37psi instead of 27psi, unless you mis-typed in one of your previous post, the AFPR isn't doing its job or you have return line/tank pressure issues.

So you're saying that when my car is idling it should be at 27psi instead of 37psi right? Ok, now its starting to make sense. I just understood that formula you posted. I will re-check the fuel pressure and vacuum to the FTS as well.

This is what I would do.

1. Make sure your gas tank is properly vented. Bottom line, your fuel pressure has to be at 27psi.

2. Check your plugs and wires.

3. Re-visit the leak test and this time start from the TB elbow so you can focus on vacuum leaks, I'm sure you're familiar with the 20psi for 30 seconds........etc. If you hear pressure leak in the crankcase let's find out why.

4. After you have fixed all leaks and able to pressurize the intake up to 20psi, adjust your TPS to around 10% at idle.

5. Properly adjust the BISS and set your idle at around 750, post back if you're not able to achieve this.

6. Check and make sure, adjust if need be, the ignition timing is at 5* BTDC.

Post back if problem persists, at least this will eliminate alot of possibilities.

Hey thanks! You've given me a good bit to work with now. I'll hit you back with what I find out.

 

[oldman]

So you're saying that when my car is idling it should be at 27psi instead of 37psi right? Ok, now its starting to make sense. I just understood that formula you posted. I will re-check the fuel pressure and vacuum to the FTS as well.

Fuel pressure and intake pressure must be maintain in 1:1 ratio, the job of the fpr. You set the base pressure to 37psi with 0psi in the intake. When you're boosting at 10psi, the fuel pressure should be 47psi (37+10). When you are idling at -20inHg (-10psi), the fuel pressure should be 27psi (37-10). The adjust ment rod and vacuum fitting on AFPR's are known to leak pressure, make sure you Taflon both of them.

Hey thanks! You've given me a good bit to work with now. I'll hit you back with what I find out.

You're welcome, good luck.

 

[RiceKiller_TSi]

Check THIS out.
Come to find out that when I disconnect the maf extension cable that the car idles PERFECTLY! So my next question is: Is this a sure fire indication of a bad GM Maf? Doesnt the ecu use some kind of default air/fuel maps when it gets no signal from the maf? Inquiring minds want to know.

 

[TurkF26]

yes the ecu will run in a safe mode kind of way when it does not get any signal from the Maf.

 

[ltvarney]

I was going to say your idling issue sounded just like a MAS problem I had on my 1G. I had disconnected the MAS for some reason and forgot to hook it back up Car wouldn't start unless I kept my foot on the gas for a few seconds, and then it was dumping fuel pretty much the whole time after that. On the highway I could see the fuel gauge moving if I boosted at all. Finally, my car sputtered and lost all power compliments of the fouled plugs, so I pulled over. At that point it seemed to be idling on 2 cylinders, really roughly. After fumbling around under the hood for a few seconds I noticed my stock MAS wasn't plugged in. After making the connection, everything went back to normal.

For that reason I would think your issue is someway related to your MAF/MAS, but I was thinking more along the lines that maybe your MAF wasn't hooked up or something. I guess it's possible that it was hooked up but just sending a horribly incorrect calculation to the ECU, and unplugging the MAF got the ECU into limp mode, which in this case was better than the incorrect readings.

Just be warned from my above example, you can get away with it while you wait on a replacement GM unit, but after a while the plugs will most likely foul. For me, all it took was a 2 hour road trip before it happened. You might also have to supply extra fuel with the gas pedal to get it started up in the morning.

 

[AL92]

I had to loctite the vacuum fitting on my old full throttle afpr.It would come loose and leak vacuum/pressure.
I went with an sx after hearing some bad stuff on the aeromotive but that was maybe just a bad batch or something and it was pretty long ago.
I actually just orded the set up from FFWD ,a bit pricey but you get nice filter,sx reg mounted on the rail and nice lines,etc.
Saves trying to find a place to mount the reg in a crowded 2g.

 

[RiceKiller_TSi]

For that reason I would think your issue is someway related to your MAF/MAS, but I was thinking more along the lines that maybe your MAF wasn't hooked up or something. I guess it's possible that it was hooked up but just sending a horribly incorrect calculation to the ECU, and unplugging the MAF got the ECU into limp mode, which in this case was better than the incorrect readings.

After purchasing a spare maf and installing it, I came to find out that the problem was with the idle settings on the maft. Don't quote me on this but I think it had something to do with the deadtime on the injectors. When I set the trims as the maft manual recommends for 580's it idled horribly and wanted to die. So what I did was just richen up the low trim (a LOT) and the thing idled better. I then increased my fuel pressure to 43.5 and it ran even better while at idle and let me remove some fuel without dying out again. I'm guessing that my fuel pressure was too low for the larger than stock injectors to work correctly at idle. Also, the settings in the guide were probably based on 43psi fp and hence the cause of my probs.

I also read on dsmchips that most injectors are flow tested at 43psi and not my stock 37 psi.
So, problem fixed.