Vacuum Problems Please help!!

[DJ23GSX]

Once in a while when i start my car and let it idle cold i notice i lose vacuum (from 20hg down to 8-10-hg) and the car almost stalls. When i try and give it gas when i lose vacuum it pops a few times then revs up. Once the car is warm it doesn't happen anymore. So far i've fixed all boost leaks and this issue still pops up occationally. What could cause this problem to only happen when the car is cold? I'm also confused why it only happens once in a while and not all the time. I would think if something was broken it would cause issues constantly unless it is something electrical thats on its way out. On days it doesn't happen my vacuum at idle is 19-21hg and i don't have any idle issues at all. Other than this pita issue the car runs very smooth.

 

[romeen]

I would start by doing a compression test and let us know the results. The expansion/contraction of various components of the combustion chamber may explain the inconsistent symptoms. Have you done a boost leak test around the time that you are experiencing the problem?

Also, I have read that an obstruction in the exhaust stream may cause vacuum to become less as engine speeds increase but have never actually seen it first hand. I imagine you would have noticeably less power and issues with spooling if that was the case so it seems unlikely. But I thought that I would throw it out there.

 

[DJ23GSX]

Yes i have done both a compression test and boost leak test a few months ago when the problem started. Boost leaks were fixed and compression was 160psi across all 4 cyls. I know boost leaks can sprout just as fast as you fix them but a few days after fixing the few minor ones i had it happened again.

It only happens at idle but when i try to drive it while the vacuum is screwy it studders and pops until around 3k rpms then it runs fine right up to redline. I've even datalogged a bunch of different parameters when this happens and nothing seems out of wack.

 

[romeen]

What is your base fuel pressure set at? When I had a problem with too high of a BFP my car would do the same thing until boost hit and then pull strong. But then again, it would likely do this all the time, not just when the motor is cold.

Have you checked your timing recently?

Also, I have read that a bad MAS can have similar problems but again no personal experience. It might be worth a search though for some more info on it.

 

[DJ23GSX]

What is your base fuel pressure set at? When I had a problem with too high of a BFP my car would do the same thing until boost hit and then pull strong. But then again, it would likely do this all the time, not just when the motor is cold.

Have you checked your timing recently?

Also, I have read that a bad MAS can have similar problems but again no personal experience. It might be worth a search though for some more info on it.

I've been searching vacuum threads for months and nothing i've found so far has been similar. My bfp is off the charts. I'm running a rewired walbro with the stock fpr right now due to my aeromotive afpr leaking. It used to happen even when the aeromotive was brand new and set at 40psi bfp. But what would change the bfp once the car is warm and cause the vacuum issue to go away? I do know that my 2g maf's adjustment screw was tampered with but again why would it only act up sometimes and not all the time. My timing was fine when checked this past summer. All the marks/teeth are lined up perfect as well.

 

[Nvisabl]

Once in a while when i start my car and let it idle cold i notice i lose vacuum (from 20hg down to 8-10-hg) and the car almost stalls. When i try and give it gas when i lose vacuum it pops a few times then revs up. Once the car is warm it doesn't happen anymore. So far i've fixed all boost leaks and this issue still pops up occationally. What could cause this problem to only happen when the car is cold? I'm also confused why it only happens once in a while and not all the time. I would think if something was broken it would cause issues constantly unless it is something electrical thats on its way out. On days it doesn't happen my vacuum at idle is 19-21hg and i don't have any idle issues at all. Other than this pita issue the car runs very smooth.

I thought about this alot one thing that comes to mind especially since you were running an after-market Fuel pressure regulator. Do you have the fuel pressure solenoid hooked up ? If so could it be hooked uo backwards? Fuel pressure solenoid is only in use during cold start-up. Also could it be hooked up on just the manifold side so when its open it vents to atmosphere?

Good luck
D.J.

 

[DJ23GSX]

I thought about this alot one thing that comes to mind especially since you were running an after-market Fuel pressure regulator. Do you have the fuel pressure solenoid hooked up ? If so could it be hooked uo backwards? Fuel pressure solenoid is only in use during cold start-up. Also could it be hooked up on just the manifold side so when its open it vents to atmosphere?

Good luck
D.J.

I've tried it both ways. Now i don't have it hooked up at all. I've got the vacuum line from the manifold going right to the fpr.

 

[tom04841]

I had the same issue with mine in the past. In my case it turned out to be two things: a loose connectionat the coolant temp sensor and a faulty coolant temp sensor....not the one wire for the gauge, but the 2 wire for the ecu. It only happened intermitantly. when disconnecting the cts harness, one of the wires broke off. I fixed that and installed a new cts. Problem never popped back up. Hopefully this is your issue and it helps some.

 

[romeen]

I've been searching vacuum threads for months and nothing i've found so far has been similar. My bfp is off the charts. I'm running a rewired walbro with the stock fpr right now due to my aeromotive afpr leaking. It used to happen even when the aeromotive was brand new and set at 40psi bfp. But what would change the bfp once the car is warm and cause the vacuum issue to go away? I do know that my 2g maf's adjustment screw was tampered with but again why would it only act up sometimes and not all the time. My timing was fine when checked this past summer. All the marks/teeth are lined up perfect as well.

Remember that the ECT sensor causes the car to run quite rich at idle until the coolant warms up to operating temp. Combine this with the already high BFP and it may explain your problem.

Did you figure out why the AFPR was leaking? Usually it is something simple like the diaphragm being installed incorrectly. I would take a look at it and try to reinstall it and get the BFP where it should be. I have e-mailed Aeromotive in the past and they seem to be pretty good at promptly responding. They may be able to help you out.

 

[DJ23GSX]

Remember that the ECT sensor causes the car to run quite rich at idle until the coolant warms up to operating temp. Combine this with the already high BFP and it may explain your problem.

Did you figure out why the AFPR was leaking? Usually it is something simple like the diaphragm being installed incorrectly. I would take a look at it and try to reinstall it and get the BFP where it should be. I have e-mailed Aeromotive in the past and they seem to be pretty good at promptly responding. They may be able to help you out.

Yes i had aeromotive rebuild it for me. It had a tear in the diaphram. They won't just send you the diaphram they need to replace it for you for some reason. I planed on putting it back in this weekend when i change my oil, cat and slave cyl. Hopefully that will fix this issue cause its a real pita when it happens and i have to drive it before its fully warmed up.

 

[romeen]

Yes i had aeromotive rebuild it for me. It had a tear in the diaphram. They won't just send you the diaphram they need to replace it for you for some reason. I planed on putting it back in this weekend when i change my oil, cat and slave cyl. Hopefully that will fix this issue cause its a real pita when it happens and i have to drive it before its fully warmed up.

Are you still using the original stock cat? I feel confident for you that this weekends project is going to solve your issues.

Let us know how it turns out.

 

[DJ23GSX]

Are you still using the original stock cat? I feel confident for you that this weekends project is going to solve your issues.

Let us know how it turns out.

No i have a RRE 3" hiflo cat thats rotted out and will be replaced with another RRE 3" hiflo.

 

[alice]

I would certainly check ignition timing and make sure it is consistent.

 

[ktmrider]

I would check the cold start-open loop items like suggested especially the coolant temp sensor. Also do you still have the fuel pressure solenoid hooked up? If it is stuck it could cause the problems you are seeing although it would also cause the car to be lean under high boost.
No direct experience on the DSM but my former Subaru had similar issues after I had bypassed the TB coolant lines. I did not see this in your posts but has it been done?

 

[DJ23GSX]

I would check the cold start-open loop items like suggested especially the coolant temp sensor. Also do you still have the fuel pressure solenoid hooked up? If it is stuck it could cause the problems you are seeing although it would also cause the car to be lean under high boost.
No direct experience on the DSM but my former Subaru had similar issues after I had bypassed the TB coolant lines. I did not see this in your posts but has it been done?

No the fuel pressure solenoid is not hooked up. All my TB coolant lines are still intact and hooked up.

If it is a bad coolant temp sensor would it send wacky reading my ecu/datalogger? I think thats about the only parameter i haven't logged trying to figure this out.

 

[romeen]

No the fuel pressure solenoid is not hooked up. All my TB coolant lines are still intact and hooked up.

If it is a bad coolant temp sensor would it send wacky reading my ecu/datalogger? I think thats about the only parameter i haven't logged trying to figure this out.

A faulty ECT sensor should trigger a CEL. I am not familiar with OBD 1 codes and datalogging. But according to my Chilton's it is code #21 (not sure if that is helpful at all).

If your logger will show it's function then check it out. If not I think it is definitely worth it to remove the ECT sensor for testing. You can use an ohmeter and a bowl of warm water to test it's function as outlined in the manual.

Are you going to reinstall the AFPR this weekend?

From my understanding the FPS is only used for warm starts so I doubt that not having it hooked up is causing the problem.

 

[ktmrider]

A faulty ECT sensor should trigger a CEL. I am not familiar with OBD 1 codes and datalogging. But according to my Chilton's it is code #21 (not sure if that is helpful at all).

If your logger will show it's function then check it out. If not I think it is definitely worth it to remove the ECT sensor for testing. You can use an ohmeter and a bowl of warm water to test it's function as outlined in the manual.

Are you going to reinstall the AFPR this weekend?

From my understanding the FPS is only used for warm starts so I doubt that not having it hooked up is causing the problem.

Some of the OBDI folks have had the sensor send a -19 degree signal to the ECU ( but no fault code ). It skews the open loop running until one or more of the other sensors triggers closed loop operation and overrides the coolant sensor.
If the FPS were to fail in the warm start position ( removes the vacuum signal to the FPR and creates a rich condition at initial startup ) the FPR would never see an actual vac/pressure signal. The hose to my FPR popped off once and caused similar conditions plus horrible fuel mileage.
One last thing to check would be the O2 readings, it could cause the lean conditions you are having too.

 

[DJ23GSX]

Well i have bit of an update. I'm not quite sure what i means yet but maybe someone can help me figure it out. No afpr yet either the old cat was stuck and took most of the day to get off.

So the problem popped up again today and for the hell of it i richened up the safc about 13% at 1k rpms and all of a sudden it idled normal again. I figured that couldn't have been it so i backed the safc back down to the original setting and there goes the vacuum again and the low idle. Raised the safc up again and idle back to normal again.

I'm wondering if my o2 sensor is going bad because at the leaner safc setting my low fuel trim was perfect. I did notice that when the problem started today the o2 sensor was stuck at .57 but its not suposed to oscillate til its nice and warm right? I've checked it before on the datalogger and it seems to oscillate most of the time but i have caught it stuck at .77 on a few occations even when its fully warmed up.

Let me know what you guys think. Would a bad o2 sensor make the ecu go crazy with the isc? The other day my car started idle surging for no reason and when i looked at the pocketlogger the ecu was raising and lower the isc from 0 up to 77 but as soon as i unplugged the isc the car stopped surging and idled fine. Might be a whole diffent problem but i figured i'd throw it out there.

Thanks