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TPS on 84 SE

 
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Rotorhog



Joined: 22 Dec 2005
Posts: 9
Location: Russellville,AR

PostPosted: Thu Dec 22, 2005 3:19 am    Post subject: TPS on 84 SE Reply with quote

Hi Blake,

I've always enjoed your site so I thought I'd take a moment to register and ask a question. I have a 1984 GSL SE with approx 91k on the odometer. It's mostly stock and very well maintained, or pampered as my wife would say. I have added Blaster II coils, K&N filter, Bonez converter. I've put Redline in the gear box, differential and steering box. The only mod I regret is the Tokico Blues and Pro Kit Springs, way too harsh on rough roads, oh well. I've thought about either a MSD or Jeff's direct fire mod but the car gets as good as 28 mpg at 65 - 70 mph so I don't really think it could improve that much more. I'll probably hold off on that one.
Anyway, I have to adjust my TPS about every 6 to 9 months. I start to see a little idle instability, especially in cold weather. I installed a new TPS sensor but no real change is evident. I adjust it per the Mazda Factory Service Bulletin update. Does anyone know why these things are so flaky? Is there some other issue that can cause the setting to drift? I get the voltage set at 10.9v on one side, 0v on the other. But when it gets squirrley the the voltage will be 10 on both sides. Does this situation cause the ECU to be unable to read the throttle opening and not go into closed loop? I know this is a lot to ask about. I've had no luck educating myself on the intricacies of the Mazda version of the L Jetronic system. I've read Charles Probst's book on Bosch systems but I get no specific help there. Thanks for your time.
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Thu Dec 22, 2005 3:49 pm    Post subject: Reply with quote

I talked to Rob about this one, since he is a Mazda Master Tech. He says that you should use the two-light method and center the adjustment, rather than the voltage method. In other words, you adjust the TPS until one light comes on (note the screw position), adjust it until both lights come on (note the screw position again), then turn the screw to the half-way point. That should get you right where you need to be. As for the drift, you should check the throttle cable for binding and the throttle stop on top of the throttle body. If the throttle plates do not close consistently to the same place, it will be impossible to set the TPS right in the first place. He also mentioned that you should always set a screw by turning it *in* (tightening). The common mistake is to turn the screw out (loosening) until the correct setting is reached, but the fastener will tend to move over time. Other than that, Rob didn't seem to think there were any big mysteries. Give it a try and let us know if that helped. If not, we can try to come up with other possibilities.
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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Rotorhog



Joined: 22 Dec 2005
Posts: 9
Location: Russellville,AR

PostPosted: Fri Dec 23, 2005 1:19 pm    Post subject: Reply with quote

Thanks Blake, I'll give that a try. I'll let you know how it works. Merry Christmas btw!
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Rotorhog



Joined: 22 Dec 2005
Posts: 9
Location: Russellville,AR

PostPosted: Mon Dec 26, 2005 6:20 pm    Post subject: Reply with quote

Tried the process Rob recomended, it did seem to work better. To clarify, when the TPS is set correctly, throttle transitions open, close are smother. No bucking and jerking at low speed. I had it close apparently but using Rob's method I got it even closer.
BUT...I went down the interstate on a 90 mile drive (Christmas visiting )with the criuse set at 75 mph. As soon as I got off the interstate I noted the idle was hung about 1500 rpms. With it still idling fast I pulled over and opened the hood. From the passenger side I grabbed the secondary throttle shaft below the TPS. No movement or effect on idle speed. I grabbed the cable from the cruise control to the bellcrank attached to the primary throttle shaft. I pulled the cable towards me and the idle slowed to where it should be.
The cruise cable seemed loose so I tightened it up. WRONG. Made the problem worse! Now it would hang at 1500 and if I blipped the throttle it would idle at 2000 rpms!
I loosened the cruise cable and reset the TPS, idle and now it's OK again. At least until I use the cruise again. Any ideas which way to go with this?
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Tue Dec 27, 2005 11:23 pm    Post subject: Reply with quote

Sounds like your cruise control throttle cable is sticking. They tend to get smashed in the hood latch if they are not properly secured. Try disconnecting it entirely and see if the problem goes away completely. The cable can be replaced, if you find it is the culprit.
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Pineapple Racing, Inc.
(503) 233-3878
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Rotorhog



Joined: 22 Dec 2005
Posts: 9
Location: Russellville,AR

PostPosted: Sun Jan 01, 2006 12:07 pm    Post subject: Reply with quote

Saturday I disconnected the cruise cable from the throttle shaft. Then I applied WD40 to the throttle shaft where the cruise attachment is affixed and brushed it (wife's toothbrush... kidding). I then shot WD40 into the cruise cable and excersized it. I don't know if this is normal or not but that cable only had about .25 inch of freeplay. With the cable disconnected I checked the throttle shaft and found it didn't close any further. So it was fully closed with the fast idle cam off the roller. I then reattached and adjusted the cruise cable (little on the loose side) and checked the TPS and idle speed.

After all of that I took her out and no throttle hang. I did go down a stretch of road in town and set the cruise. It worked OK and didn't hang after I disengaged it. The real test will be going down the interstate with it engaged for an hour and see what happens then.

Maybe I have a flaky cuise module. It's always 'hunted' a bit oscillating up and down on level road about 1 to 2 mph from set point. I don't know enough about these units to know for sure. I'll keep us posted on how this works out. Later!
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Blake
Been there, done that


Joined: 12 Jul 2005
Posts: 135
Location: Portland, OR

PostPosted: Sun Jan 01, 2006 9:40 pm    Post subject: Reply with quote

If you do take a closer look at the cruise control module, you might want to check for "cold" solder joints. With age and vibration solder joints can crack and, thus, stop conducting entirely or intermittently. Series 4 (86-8Cool 2nd gen RX-7s are notorious for this, particularly the LOGICONs and warning light clusters. 1st gens usually don't have many electrical gremlins, but that's because they are much simpler animals. Anyway, that would be something to take a look at...or, rather, just fix as a precaution, since it's a hard problem to spot because the cracks are pretty much invisible. I just take a soldering iron and touch it to each solder joint, melting it and letting it resolidify. It only takes a short time to do and you will at least be sure that's not the problem.

Just a thought...
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Blake Qualley
Pineapple Racing, Inc.
(503) 233-3878
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Rotorhog



Joined: 22 Dec 2005
Posts: 9
Location: Russellville,AR

PostPosted: Mon Jan 02, 2006 11:27 am    Post subject: Reply with quote

Blake, if I have to keep chasing this I'll certainly keep that in mind and look for it. You're observation about cold solder and 2nd gens is well spoke. I can attest to the joys of removing and resoldering the HVAC Logicon and warning cluster on my 88 GTU. I like the 2nd gens but I'll take a 1st gen any day for reliability and ease of maintenance. Thanks to you and Rob for trying to help me with these issues and Happy New Year!
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