Dash pot is and old old name, stolen from carburetter and used for 2 things, slowing the throttle or raising idle speed for A/C on and other reasons. See the idle out of control page?
It does not fit on the dash, nor is it pot. but...
It is also called vacuum servo actuator or vacuum motor.
I will call it, a Dash Pot. Like Suzuki does.
Reason it exists:
The TBI engine runs a wet intake system and loves to puddle fuel in the intake runners, this is why Calif, ("A.R.B") banned it in 1994.
This Device raises the throttle valve, and RPM real high at idle, more than the IAC thermal valve can do.
It runs for 3 to 30 seconds, on any cold or warm start, hotter is shorter time. (ECU decides this and uses the Dashpot VSV valve to activate it)
There is a spring hidden inside it. See Calibration of the DP here.
Photo #1:
This part above, only fits to 89-95 8 Valve 1.6L TBIw 91+).
The MPI G16B engine does not run a wet manifold, so is devoid of such a device.
Common question:
My rubber boot looks bad, answer, so what ! after 26 years you expect rubber to look good? it still works, run it. Ever price a new one? (I think nobody sells it ,now)
My spring is dead, that is a sure sign of a bad Dashpot.
1989 to 1995
You are here because, it never retracts.
See this DP video on how it works that hand applied vacuum .
Symptoms, you have a too fast an idle, all the time. hot or cold. ?
Just one look at the DP device, end and see if it is fully retracted, after 30 seconds. If not?, it's failing.
DP focused theory and facts:
This DP , in the 8v Sidekick is called a "Cold start Fast idle device."
A tech, knows what it really is, it's a slave vacuum diaphragm. (<it can be tested with any hand held vacuum pump to 8 inches of HG. 0.27bar, or 27KpA )
Fact 2, it is also internally spring loaded. ( this hidden spring opens the throttle with no vacuum applied.
Fact 3, the ECU controls it , at all times.
Here is how it works. (open hood of car, see USA vacuum map?, (look up) see vacuum routing to the DP VSV? (vacuum solenoid valves)
Check 1:?
Are the DP hoses routed correctly and to the correct nipples at both ends? of the DP and all VSV nipples? (VSV polarity counts !)
DP Tests: (there are many , all are simple)
Ignition Key off, (see photo of TB below.)
Test 1:
The DP internal spring presses on the throttle and holds the throttle open about 3mm.(MY DATA)
if not?, THE DP IS BAD, or the spring inside is BAD{rusted},or
or some BAD GUY, fiddled the DP screw to render it useless. (unscrewing that calibration screw will mess this all up)
Test 2:
Key off , the DP is extended.
Key on, the ECU boots up DP is extended 3mm. still.
You then Key on and start the engine; now the ECU does its magic here using the VSV valve. just 1 time.
The engine starts, and then.....
After 10 to 30 seconds delay OF RUNNING HOT OR COLD (water coolant temp based ) HOT STARTS, RETRACT FASTER.
(don't worry this time delay, the ECU KNOWS what it's doing here. colder fuel takes longer to evaporate, fuel physics... )
The VSV vacuum air valve OPENS say at 15seconds., and plenum vacuum (19inches HG) exits the VSV port and lands on the the DP, it then retracts )
This vacuum hits the DP and it sucks back fast. Extreme fast idle now ends, and cold idle is mostly controlled now by the IAC thermal valve.
IF the DP fails to RETRACT then the DP diaphragm is ruptured, or the VSV is bad.
Test 3: (it didn't suck back)
At this moment, pull the DP hose at the DP end. (behind TB) TB ,means, Throttle body, on all cars, made.
Idling (way too fast) now...
Is the hose in your hand sucking air now , feel it with your finger tip, fell it suck real hard? ( all mech.'s, know how to work with vacuum controls)
yes, it sucks good, so VSV now open and working but , but we see the bad DP slave. (do a text book diaphragm leak down test on the DP) fails? bingo bad DP.
No VSV suction,?, that is a bad VSV or bad ECU command. (and as always, the wires, the DP wires are bad)
Or the VSV vacuum input port is not at a hard vacuum. That means the hoses is clogged or the TB plenum nipple to it is clogged. clean it and all is good. (hose cracked)
The VSV has vacuum to it at all times running
the VSV only job is to open on engine start then go close at all times runnning and driving.
Electrics:
I have plenum vacuum to the VSV input port (good). so..... we now attack Electrical.
Test4:
I then measure voltage across the 2 pins (plugged in, idling) I use standard industry (automotive) back probing methods.
I read:
12 vdc, good (ecu is commanding the DP to retract) ( any voltmeter or DMM works from a $3 meter up to any cost, or a Fluke 88AV)
0 vdc, bad, ECU is malfunctioning. (the ECu can be bad, (ECU stuck in backup mode, its bad, and it knows it's bad)
Even the transistor that drives this VSV can be bad (insanely rare), or lost 12v power to the VSV.
Engine stopped, key off.
Test 5:
I look again and make sure the hoses are routed to the correct nipples. (yes, polarity counts)
I check the VSV coil, (I remove IT'S ,LOCKED connector, no forcing! Suzuki don't sell spares! ) and it reads, 27ohms (about,) not 0 shorted or infinity burned open coil.
The coils is just that, a copper electromagnet coil of wire.
My DMM is on OHMs (resistance R200 range) is touching only the 2 VSV actual pins, on actual VSV device)
Noobs, use a manual ranging DMM, Autoranging meters takes skill and practice to understand it.
(if you must use at AUTO ranger , practice on resistors, shorts and opens , FIRST)
Advanced testing (maybe a cure) HOPE: test 6 passes!
Test 6:
Next: (VSV not plugged into ECU or harness conn.engine off.)
I remove it. from the car, and bench test it.
I apply 12vdc to it's 2 pins, and I hear it click. click good, no click bad. (no polarity rules here)
I attempt to clean it, I use CRC MAF cleaner spray , as it is safe for PLASTICS.
I attempt to back flush all its nipples, and make sure the filter is not clogged, it if has one.
I try hard to get the clicking to work. if not , DOA the VSV. if yes, it now clicks I then do the VSV tests, below.
The VSV is 3 way valve and is polarized, the hoses must be connected correctly! (due to the vacuum bleed off feature,via the vent filter, inside)
The VSV tests are here.
the DP system only has 4 parts. and lots of ways to mess up.... Fate is cruel. (each part, or simple filth clogging up the works)
Parting shot. (crying towel)
If the ECU never applies 12vdc to the DP VSV
then:
1: ECU is bad. (crazy rare for this port tof fail only)
2: ECU is in backup mode,.bad ECU.
12vdc is missing to the VSV, broken wire. see my schematics page for easy trace of that path.
I don't think Limphome kills the DP , but for sure it kills idle controls, via the ISC device on right side of throttle body.
Don't confuse bad idle controls with a bad DP.
Idle is complex. so are all the ways to cause a bad idle with a perfect ECU,DP .
Most important!, IDLE works right
LAST! In most cases,a bad idle is just a symptom of a far greater more important failure.
But watching the action of this device below, is always a first check, to be sure it's working actively.
The below photo shows, how the parts were fitted in the factory , holding the throttle open 3mm (about). (89-95')
On a Hot running engine. The DP is retracted full time, (you will see a gap in the DP right end of rod), The IAC (thermal ) is closed 100% and the ISC regulates the idle.
The hot idle speed bleed screw is on the front side of this below photo. (has a black plastic cap covering it) Only this device sets 800 RPM HOT.
That gapping pit in the center is the injector mount.
Photo #2 is 1991 example, ignore funny looking ISC on right side if you have 1989/90 car. Never touch screw applies to all cars 1991 and newer.
DP Calibration:
This setting is the last thing to ever touch ,if ever. All other calibrations and functions must be GOOD first. ALL.
All idle effecting air leaks must be cure first.
- Best practice, is to leave it alone. The ECU is tuned
for it to be working. (I have no FSM links
here )
- If the engine is not fully tuned up, and running perfectly , adjusting this device is futile. (Cam timing correct, Spark timing dead on spec.) (TV , IAC devices not leaking air.)
- No accessories on, no Head lamps, Dash fan, no A/C , no
Defrost, and in simple words, the ECU is not in fast idle mode,
the 89/90 has many fast idle inputs. !!!
- No illegal intake air leaks, allowed. If the engine races over 850 RPM hot, in normal DP retracted mode, see #2 ,stop , go back....
- The TPS idle switch must go from closed to open when the DP
is activated manually or the ISC servo will FIGHT YOU. This Calibration is the idle switch OPEN, never
closed.
- Engine hot 180F + And running in Closed loop mode. (not limphome or open loop)
- Start the engine,
- The DP retracts (with a gap), 30 seconds (max) after starting engine. IF not,? stop, it's bad. fix bad first, you can not calibrate any bad DP.
- Next,
pull the DP vacuum hose and insert a GOLF TEE into sucking hose.
The idle will be fast now DP activated. The Idle switch must be open
now , reads 5v at TPS.
- Set the center DP screw seen in above photo, just
below the fuel Line port, to 2500 RPM IDLE (this is factory
spec. from an FSM) Some guys like it lower so set it lower in
warm climates.
- You are done. put back the vacuum line.
The word Mikuni corp. is seen on top of the IAC.
TV is that BRASS yellow part. Seen here with DP 1991-95 fully retracted, setting ZERO TV AIR SUPPLY,
The 89/90 the TV gap, DP retracted is a Dutycycle calibration proceedure. (this gap)
In 1991and newer G16 engines. (all) this valve is closed 99.9%
If the ISC leaks air, or the IAC leaks hot. these steps here, will be useless.
The can be no extra or illegal air leaks now, by any means,
The 1991 below looks like this with the DP retracted. (about .0005" gap ) the 1989/90 the gap will be larger after calibrating Duty cycle, correctly at to 50%
Photo #3: Top view, with top of Throttle body air horn casing removed (to see this nasty gasket that loves crack and suck on and destroy idle speeds.
v:5------------1/16/13