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Dodgy connection somewhere.....

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I went and did a voltage check on the power to:

  1. PURGE VALVE
  2. SECONDARY AIR INJECTOR VACUUM SOLENOID

Both have same 7 volts. Electrics are not my bag….

Would I be wrong in assuming voltage loss due to a bad ground?
Do both these systems share the same grounding point?
Would anyone have a wiring diagram of the electrical system for the SAI system?

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Ground is supplied by the engine ECU. They both share the same supply from fuse 26 which also feeds the MAF, ECU box fan, O2 sensors and cam position sensor on a Brown/Pink wire. See pages A1, page 4 for a description of how it works and A1 pages 8 and 15 in the ETM for the relevant bits.

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Could the 7v be a digital multimeter reading of a 12v PWM signal (so in reality the parts get expected voltage... but because the power isn't constantly on the multimeter reads pseudo average voltage)? For sure purge valves are quickly pulsed as opposed to being held constantly open.

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Failing all else, would there be a known work around this bloody “save the world” SAI system that will stop my vehicle from stuttering every time i start it when warm?

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Up here it is simply removed and blinded.

th.

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@LPGC, no it isn't a PWM signal, it is a permanent live directly from the fuse (via a splice) with the ground,either permanent or pulsed supplied from the ECU. So provided he is testing the voltage with respect to ground and not across the pins, it should show full battery voltage.

If the SAI isn't needed to pass emissions in your particular US State, then it can be removed. All you need to find is some blanking plugs to blank the holes in the cylinder heads. Once they are blanked the rest can be taken out and removed. Not sure if that will throw a fault code or not though. If you disconnect it and check for any SAI related codes you may have to put a resistor in place of the solenoid to fool the ECU. The purge valve is a separate system and even on a UK car if that is disconnected you will get a code thrown.

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For the record, I think the things California forced on the auto industry were a bit draconian. I am not a fan.
They were however, effective in cleaning up the air quality in Southern California..........
Eliminating the NAS emissions is perhaps not a good idea as more states are starting emissions testing.
Remember the testing programs are worth millions of Dollars / Pounds/ Kroner....etc.....as it is basically another
form of tax, so why not jump on the Greenwashing gravy train? (Petrol evil, E/Vs Gooood)
Not having the correct parts is an instant fail. you eliminate the system, the resale is going to go down. If the issues
you are having are emissions related, simply re installing the parts will re install the initial issue.
That just makes it someone else's problem down the road. I would hate to see more P-38s
in wreckers yards due to failed emissions tests.
I think there would be several codes thrown if it is all removed as well. Possibly getting an ECU from UK would be the answer to that one?

Just my 2 cents, now back to your regularly scheduled problem...........

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I don’t have SAI on either my 97 P38 or 01 D2, but l understand from the D2 site I frequent (Landroverforums) that you will get a code if you remove it.

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Depending upon the year, you will probably get several. For example, 99-02 has an additional temp sensor on the bottom of the Rad which works with SAI, so it will probably be upset as well.......
I wonder if setting the market to UK from NAS would do it, or if you would need a UK ECU?

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I've got a spare UK Thor ECU..... You only need the Nanocom to copy and paste the initialisation code from ECU to BeCM.

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Gilbertd wrote:

@LPGC, no it isn't a PWM signal, it is a permanent live directly from the fuse (via a splice) with the ground,either permanent or pulsed supplied from the ECU. So provided he is testing the voltage with respect to ground and not across the pins, it should show full battery voltage.

Yes of course, pulsed on the negative not the positive.

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Well, Pulsed, but at what frequency? and at what point is a switched supply considered to be PWM?
In other words, if one was looking at the signal relative to B+, what would you normally see for pulse duration?
If it was not bucketing down right now, I would go check to see what I get.

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As it's operating a solenoid, I would suspect at a pretty low frequency or it wouldn't get chance to operate before it released. Then again, I would expect the SAI to operate for a set time rather than being pulsed.

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FWIW, I did the voltage test between pins. When sun arises in AM I will check all the above from the earth point of battery and report back. In my defense, I did state in post that electricity os not my bag….

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I can say that the SAI blower runs for about 30 seconds when starting from cold.
Would it be safe to say that the solenoid stays active for the same time?
Does your SAI blower activate?

In your earlier tests, are you sure you were getting 7.3 volts, not .73 volts?
.73 would be a typical voltage drop when a power transistor is switched on

When you do your tests, try from B+ to the active pins as it was mentioned earlier that it is a negative switched signal.
Theoretically, you should get 0v from B- to the pins when active (Perhaps point 73v as it is a transistor)
When B- is switched, you will get full battery voltage from B+ to the switched lead when active

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Bolt wrote:

Well, Pulsed, but at what frequency? and at what point is a switched supply considered to be PWM?
In other words, if one was looking at the signal relative to B+, what would you normally see for pulse duration?
If it was not bucketing down right now, I would go check to see what I get.

I used the term PWM very loosely, I'd guess the usual pulse frequency of evap purge valves to be around 5 pulses per second (5 pulses of full battery voltage) and pulse durations of around 0.1 seconds. So not PWM in the usual sense.

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Not being nit picky, just wondering what the parameters are in this case.
All of my PWM experience is with the old style PWM solar chargers. Those went from about 1 minute to 400hz +

Nice to know what to look for when trouble shooting this system.
Thanks!

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Just check all power to the various SAI items. 12v is being powered to all parts. All the electrical equipment associated with the SAI are new items and still this stutter 15 seconds after a warm engine start.
With all the knowledge here on the forum there surely has to be an answer to this. Im using top grade fuel, did a Seafoam run twice. Coils, leads and plugs are all 6 months old.

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Unless your lower grade fuel is really poor, a P38 doesn't need top grade stuff. Recommended fuel is 95 RON which equates to 90 in the US as a different method of grading is used (AKI or (R+M)/2).

As it appears to be an SAI problem, there is limited knowledge here to help as only NAS cars had it fitted. Reading about it in RAVE, it appears that it should only operate on a cold start and not a hot start so it could be caused by a temperature sensor problem. I understand on later NAS cars, there is an additional one in the radiator, presumably earlier ones just used the engine sensor.

RAVE says:

The engine control module (ECM) checks the engine coolant temperature when the engine is started, and if it is below 55°C (131°F), the SAI pump is started. Secondary air injection will remain operational for a period controlled by the ECM and is dependent on the starting temperature of the engine. This varies from approximately 95 seconds for a start temperature of 8°C (46°F) to 30 seconds for a start temperature of 55°C (131°F). The SAI pump operation can be cut short due to excessive engine speed or load.