P0503 Error

[MikeyLikesIt]

I'm getting a P0503 VSS error. It seems my RPMs seem to hang around 1100 or so then drop down. I think my idle is setup fine, but I keep getting this error code. I've never done any work or even know exactly where the VSS is, but is it attached to the transmission somehow? Or am I barking up the wrong tree on this one?

Now I did extend the wires for the TPS and the IAC. Could it be related?

Thanks!

Mike

[FormerDatsun510Man]

That codes means the ECU is receiving either an erratic or high speed from the speed sensor. I would check to make sure the PC Pro patch cable and wiring is secure and also the speed sensor (bolts in the tail area of the transmission is) bolted in firmly and the wiring intact. Perhaps remove and inspect the speed sensor for damage to the plastic gear?

Bill

[MikeyLikesIt]

OK, I'll take a look. I won't have to drain the trans, will I?

[Steve in VC]

OK, I'll take a look. I won't have to drain the trans, will I?No, but jack / jackstand the car from the passenger side to move the oil further away.

The bolt uses a 10mm socket.

[MikeyLikesIt]

That codes means the ECU is receiving either an erratic or high speed from the speed sensor. I would check to make sure the PC Pro patch cable and wiring is secure and also the speed sensor (bolts in the tail area of the transmission is) bolted in firmly and the wiring intact. Perhaps remove and inspect the speed sensor for damage to the plastic gear?

Bill

May be a PC Pro issue. On the way home, any time I gave it a bit more than minimal gas, the A/F dropped to 10.0. So I nursed it the rest of the way home. Will take a look for a loose connection or vacuum line on the PC Pro.

Mike

[Steve in VC]

May be a PC Pro issue. On the way home, any time I gave it a bit more than minimal gas, the A/F dropped to 10.0. So I nursed it the rest of the way home. Will take a look for a loose connection or vacuum line on the PC Pro.

MikeDid you enter boost when the A/F dropped? If not, the PC-Pro's shouldn't get involved (still could be a harness problem).

Unplug the PC-Pro's, reinstall the stock harness into the ECU (pull the drivers seat - makes it much easier). Tie the bypass open.

If the problem goes away, check the PC-Pro harness
1. Pull gently on each wire, bend each wire at it's connection to see if there are any broken wires
2. Look for any abrasion or cuts that may be shorting to the chassis.

[MikeyLikesIt]

This has now morphed into a P0507 error. RPMs sit at around 1200, for several seconds, then drop to around 850.

Another vacuum leak? Or an IAC issue?

[MikeyLikesIt]

*Update*
Hmm, I've been researching, and I did clean the BTB with some carb cleaner. Did I strip the plastic coating from the butterfly valve?
:taz:

[MikeyLikesIt]

Still have the roaming RPM with a P0507 error. Can't seem to get the RPMs to settle... Doesn't seem to be a vac leak, though I am wondering if it is a PC-PRO wiring issue... The A/F drops to under 11.0 once I go into boost. It never seemed to do this before...

Any other ideas?

Thanks!

Mike

[MikeyLikesIt]

*Update*

I've disconnected the PC-PRO and remove the SC belt. Idle issue still exists. Going to take a look at my wiring next as I extended the IAC and the TPS lines...

[MikeyLikesIt]

OK, I've cleaned up a few more vac leaks and soldered my connections for the TPS and the IAC.

The check engine has cleared, and it idles fine (minus the occassional idle dip), but now it seems that when I should be seeing boost, I'm not. I hear the blower get the load on it, the A/F change appropriately, but I'm not feeling the power? Possibly the belt is slipping, but I don't think so. I got under the hood with it running and the belt doesn't seem to be slipping, it's a new belt I just put on... Maybe a crimped vac line?

I feel like I am fixng problems only to create more:confused:

Thanks guys again for all your help!
Mike

[FormerDatsun510Man]

If you aren't getting boost and yet the blower is spinning, the most likely culprit is the bypass valve actuator is not closing off when it should. Verify you have vaccuum to the bypass valve actuator and it is opened while idling. Then blip the throttle. You should see the bypass valve actuator close when that happens. If not, you found the problem.

To clarify, the bypass valve actuator lever is supposed to be pulled (open) when it sees high vacuum, thus when idling and cruising. When you see boost, the vacuum drops off and the valve actuator lever will push back out, which closes the bypass valve and allows the supercharger to generate full boost.

The other possibility is if the vaccuum line you use for the boost gauge is leaking. If this also is the same line that you are using for the PC Pros, this would also cause the same symptoms. What would actually be happening there is that the supercharger is making boost, but the gauge isn't measuring it and also that since the PC Pros are not adding fuel it is falling flat because it is going way lean.

Bill

[MikeyLikesIt]

You guys were right (Bill and Tom). I just had to make myself look at the bypass to see it was stuck open. I swapped it out with the old one and it's fine. Seems there's an issue with the new one I got. I'll have to see if I can free it up or maybe send it back.

All is well, now I am just left with the idle dip when it's cold. I need to tweak my RPMs this weekend.

You two are a credit to your profession. Thanks for all of your help.

[FormerDatsun510Man]

If you have the big TB, turn the idle screw about a 1/4 turn clockwise. If you have the stock TB, turn the idle air bleed screw about 1/2 turn counterclockwise.

[MikeyLikesIt]

I did that this morning, seems to be better, I'm reading 850-880RPMs on my scanguage... Maybe need a bit higher to get it to clear. I amy attempt some Seafoam this weekend to see if it smoothes it out any.