Failed dashpots?

vrracing · 08-03-2009, 09:15 PM

90 vert with recently built JDM Tii. New TPS, the car idles and runs beautifully. The idle is rock solid at 750.

The only problem is that when you let off the gas the car will often die. The rpms drop to almost zero (there is a final big mark on the tach which I assume is supposed to be 500). Sometimes it recovers and sometimes it dies.

Should be the dashpot. So I swapped in the one from the NA. Before installing the NAs into the Tii I compared them and they both provide the same resistance.

However, it didnt change. Adjusted it with the TPS as per the FSM. No change. If I rev it to 4500 and let off, you can see the TPS slowing the throttle return but it is fully bottomed out by the time the tach reads only 3000.

Are dashpots a common failure? Any good sources for a replacement?

Thanks,

Jim

NoDOHC · 08-04-2009, 12:06 AM

I had the same problem on my '91 and to solve the problem, I adjusted the dashpot outside the factory specs (tightened it in further). If you go too far, the throttle will be held open (not desirable).

You should also look into your ignition timing.

Did you just get the 'vert together with boost, or have you had it for a while?

I have a good friend (not on here) with a turbo 'vert, they are cool.

vrracing · 08-04-2009, 09:33 AM

Yeah, screwing it in all the way didnt have any effect. The timing is perfect and the car runs beautifully except for the stalling when letting off the throttle.

Gets your attention when slowing for a light, the engine dies and the power brakes disappear!

We've had the car for 3.5 years, built and installed the engine last year. Took a while to debug vacuum leaks but it's really good now.

Two weeks ago we installed a Stayfast cloth top from ConvertibleTopGuys.com. Wasnt as bad as I expected. We took both Sat and Sun but we took a lot of breaks to watch the Brickyard and it was 105 out so breaks were necessary. It turned out really nice. I've always liked cloth tops a lot more than vinyl.

We used the Pineapple templates for porting, stock intake/turbo/intercooler, RP downpipe, Bonez cat and Corksport exhaust. Controlling it with a RTek1.8 with 720/1000 injectors and an SAFC (hopefully interim solution until RTek gets the 2.0 out for S5s) to control the AFR which we monitor with a Zeitronix. Stock boost and it's plenty fast but there is headroom.

Rotary Inspired · 08-05-2009, 05:10 PM

Sounds like the ECU could not be giving it fuel as it returns to idle. I can't remember much about the stock system as I generally rip it out for a haltech. But you need the fuel start back somewhere between 1600 and 1300 rpms on deceleration from my experience to get the best driveablity. Does the Rtek allow you to make these adjustments? sorry no help on the dashpot my car no longer has the stock TPS.

vrracing · 08-06-2009, 10:00 AM

Its an RTek1.8 (the 2.x arent available for S5s yet) so no adjustments are available. But I guess I could richen up the mixture at lower RPMs via the SAFC... Hmmm...

I was wondering if opening up the butterfly valve on the throttle body would work. I set it as well as I could without wire-style feeler gauges.

Rotary Inspired · 08-06-2009, 11:32 PM

Is the motor ported? I find that a pretty large primary port likes closer to 1000 rpms.

vrracing · 08-07-2009, 07:11 AM

Yes it is ported with the Pineapple templates.

I think my plan for now will be to put the new dashpot in when it arrives from Malloys on Monday or Tuesday. If that doesnt work I'll count how many turns out the BAC idle screw is at and then if there is some downward adjustability I'll open the throttle plate up a bit then adjust the idle back down with the BAC. I'd rather not have a 1000rpm idle. The porting isnt radical, it idles perfectly at 750 and the car is loud enough as it is.

Thanks!

NoDOHC · 08-07-2009, 06:33 PM

Exhaust porting makes it louder, but the turbo should quiet it down a little.

Are you running an aftermarket lightweight flywheel? If so you will need to restore fuel at 2000 rpm or so to keep it from stalling (it drops off too fast).

I really doubt that the dashpot is the issue.

When are you going Haltech?

vrracing · 08-08-2009, 07:26 PM

Yes, we are running a lightweight flywheel. One of the ACT Streetlights not the Prolight.

Not going Haltach. Really just want it to work. Don't need big power. As I recall going standalone requires a bunch of workarounds for a/c, wipers, etc. Not really interested in spending more money or time on the car.

By adding fuel you mean richening it up below 2000?

Boostmaniac · 08-10-2009, 04:12 AM

By adding fuel he means that when the TPS reads 0 percent on a rev fall down the fuel injectors stop functioning to save some gas. They usually kick back on ~ 1400 rpm so it doesn't bottom out and die. Since a light weight flywheel will lose RPM faster, you need to kick the fuel back on at a higher RPM so it can catch it and let it idle.

Kick on the injectors sooner and increase idle to ~900.

vrracing · 08-10-2009, 06:48 AM

Ah, that sounds like a standalone-only capability. I have the stock ECU with an RTek1.8 and a SAFC so I have no way to change that threshold number. It's odd that with all the searching I did during my research on the flywheel that I never saw a requirement to have a standalone.

If your theory is correct, then raising the idle should have no effect. The injectors are off, they come back on at 1400 but the rpms drop off too fast and the engine dies. The idle value wouldnt come into effect yet. If the 1400 number was based on the idle speed, then raising the idle would raise that 1400 threshold.

I wonder if changing the low throttle point on the SAFC to zero and richening up the low rpm map would get enough fuel in those few squirts it gets from 1400 to zero would be enough to fix it...

We tried the graphite exhaust gaskets and unfortunately the one between the exhaust manifold and turbo blew out last week. So gotta get those replaced before I can play with this again.

And the kid takes the car back to school on Friday. Gonna be one of those weeks!

NoDOHC · 08-11-2009, 05:36 PM

If you richen the high vacuum low speed map up (so that it only happens at 0 throttle) you may have enough to save the engine from stalling. I will find out once I get my lightweight flywheel and clutch on my '86.

08-03-2009, 09:15 PM	#1
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Failed dashpots? 90 vert with recently built JDM Tii. New TPS, the car idles and runs beautifully. The idle is rock solid at 750. The only problem is that when you let off the gas the car will often die. The rpms drop to almost zero (there is a final big mark on the tach which I assume is supposed to be 500). Sometimes it recovers and sometimes it dies. Should be the dashpot. So I swapped in the one from the NA. Before installing the NAs into the Tii I compared them and they both provide the same resistance. However, it didnt change. Adjusted it with the TPS as per the FSM. No change. If I rev it to 4500 and let off, you can see the TPS slowing the throttle return but it is fully bottomed out by the time the tach reads only 3000. Are dashpots a common failure? Any good sources for a replacement? Thanks, Jim

08-04-2009, 12:06 AM	#2
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	I had the same problem on my '91 and to solve the problem, I adjusted the dashpot outside the factory specs (tightened it in further). If you go too far, the throttle will be held open (not desirable). You should also look into your ignition timing. Did you just get the 'vert together with boost, or have you had it for a while? I have a good friend (not on here) with a turbo 'vert, they are cool. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

08-05-2009, 05:10 PM	#4
Rotary Inspired Rotary Fan in Training Join Date: Feb 2008 Location: SW OKC iTrader: (0) Posts: 75 Rep Power: 17	Sounds like the ECU could not be giving it fuel as it returns to idle. I can't remember much about the stock system as I generally rip it out for a haltech. But you need the fuel start back somewhere between 1600 and 1300 rpms on deceleration from my experience to get the best driveablity. Does the Rtek allow you to make these adjustments? sorry no help on the dashpot my car no longer has the stock TPS. __________________ If you wanna become ASE certified buy the RX7.

08-06-2009, 11:32 PM	#6
Rotary Inspired Rotary Fan in Training Join Date: Feb 2008 Location: SW OKC iTrader: (0) Posts: 75 Rep Power: 17	Is the motor ported? I find that a pretty large primary port likes closer to 1000 rpms. __________________ If you wanna become ASE certified buy the RX7.

08-07-2009, 06:33 PM	#8
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	Exhaust porting makes it louder, but the turbo should quiet it down a little. Are you running an aftermarket lightweight flywheel? If so you will need to restore fuel at 2000 rpm or so to keep it from stalling (it drops off too fast). I really doubt that the dashpot is the issue. When are you going Haltech? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

08-04-2009, 09:33 AM	#3
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Yeah, screwing it in all the way didnt have any effect. The timing is perfect and the car runs beautifully except for the stalling when letting off the throttle. Gets your attention when slowing for a light, the engine dies and the power brakes disappear! We've had the car for 3.5 years, built and installed the engine last year. Took a while to debug vacuum leaks but it's really good now. Two weeks ago we installed a Stayfast cloth top from ConvertibleTopGuys.com. Wasnt as bad as I expected. We took both Sat and Sun but we took a lot of breaks to watch the Brickyard and it was 105 out so breaks were necessary. It turned out really nice. I've always liked cloth tops a lot more than vinyl. We used the Pineapple templates for porting, stock intake/turbo/intercooler, RP downpipe, Bonez cat and Corksport exhaust. Controlling it with a RTek1.8 with 720/1000 injectors and an SAFC (hopefully interim solution until RTek gets the 2.0 out for S5s) to control the AFR which we monitor with a Zeitronix. Stock boost and it's plenty fast but there is headroom.

08-06-2009, 10:00 AM	#5
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Its an RTek1.8 (the 2.x arent available for S5s yet) so no adjustments are available. But I guess I could richen up the mixture at lower RPMs via the SAFC... Hmmm... I was wondering if opening up the butterfly valve on the throttle body would work. I set it as well as I could without wire-style feeler gauges.

08-07-2009, 07:11 AM	#7
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Yes it is ported with the Pineapple templates. I think my plan for now will be to put the new dashpot in when it arrives from Malloys on Monday or Tuesday. If that doesnt work I'll count how many turns out the BAC idle screw is at and then if there is some downward adjustability I'll open the throttle plate up a bit then adjust the idle back down with the BAC. I'd rather not have a 1000rpm idle. The porting isnt radical, it idles perfectly at 750 and the car is loud enough as it is. Thanks!

08-08-2009, 07:26 PM	#9
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Yes, we are running a lightweight flywheel. One of the ACT Streetlights not the Prolight. Not going Haltach. Really just want it to work. Don't need big power. As I recall going standalone requires a bunch of workarounds for a/c, wipers, etc. Not really interested in spending more money or time on the car. By adding fuel you mean richening it up below 2000?

08-10-2009, 04:12 AM	#10
Boostmaniac Rotary Fanatic Join Date: Apr 2008 iTrader: (0) Posts: 182 Rep Power: 0	By adding fuel he means that when the TPS reads 0 percent on a rev fall down the fuel injectors stop functioning to save some gas. They usually kick back on ~ 1400 rpm so it doesn't bottom out and die. Since a light weight flywheel will lose RPM faster, you need to kick the fuel back on at a higher RPM so it can catch it and let it idle. Kick on the injectors sooner and increase idle to ~900.

08-10-2009, 06:48 AM	#11
vrracing Rotating Assembly Join Date: Oct 2008 Location: TX iTrader: (0) Posts: 102 Rep Power: 17	Ah, that sounds like a standalone-only capability. I have the stock ECU with an RTek1.8 and a SAFC so I have no way to change that threshold number. It's odd that with all the searching I did during my research on the flywheel that I never saw a requirement to have a standalone. If your theory is correct, then raising the idle should have no effect. The injectors are off, they come back on at 1400 but the rpms drop off too fast and the engine dies. The idle value wouldnt come into effect yet. If the 1400 number was based on the idle speed, then raising the idle would raise that 1400 threshold. I wonder if changing the low throttle point on the SAFC to zero and richening up the low rpm map would get enough fuel in those few squirts it gets from 1400 to zero would be enough to fix it... We tried the graphite exhaust gaskets and unfortunately the one between the exhaust manifold and turbo blew out last week. So gotta get those replaced before I can play with this again. And the kid takes the car back to school on Friday. Gonna be one of those weeks!

08-11-2009, 05:36 PM	#12
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin iTrader: (1) Posts: 855 Rep Power: 17	If you richen the high vacuum low speed map up (so that it only happens at 0 throttle) you may have enough to save the engine from stalling. I will find out once I get my lightweight flywheel and clutch on my '86. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)