Junk parts are a pain.

[Sam Powell]

I had a good tuning day today, but the IAS stuck at 20% part way through the session. It unstuck when I cut it off and started it again. Then when I got home, the TPS quit responding. It registered a low voltage, but not a high one. I have another junk part, and will check them both out, but the IAS and the TPS came off of an old 85 Buick in the junk yard. I know '85 seems new, but after all this is GM stuff, and electronics at that. This makes me question the wisdom of using recycled parts in this hi-tech application. It has to be pretty crusty from sitting out there in the weather and having mice and squirrels nibble on it.

I was too tired, and it was too late for me to fiddle with it tonight, and I won't get to it for maybe almost a week now. So she is garage bound again. It's going to be awhile before I will trust driving it very far from home. It hardly seems like Mopar in that regard.

Some of you know that I am a piano tuner by trade. Learning to tune pianos is a very, very difficult thing to do. So hard in fact, that if I had known how hard when I started learning I would never have tried. Now, after 40 years (more really), I can say I have made really good money, and had a great deal of fun with this skill. So, I am glad I didn;t know how hard it was when I started. The same thing is kind of true of this EFI project. I don;t think I would have had the guts to try this if I had known how involved it would be, and how long the car would be off the road. Neither of these problems have anything to do with the ECM, or management system. They are just inherent in the design of modern EFI. I kind of hope the EFIt turns out as good as the piano tuning thing did
OK, so maybe the bottom line is I am still learning even at my advanced age, and maybe that will keep me young.

_________________
A REAL professional is someone who knows when to hit it with a bigger hammer.

[slantzilla]

Sam, I have always questioned using junk yard parts for something like EFI, especially GM stuff. It really wasn't that good when it was new.

I do truly admire you guys who are doing the EFI stuff though.

_________________
Proud supporter of Mike Jeffrey Racing Engines since 1999.

[LUCKY13]

Yea it will be worth it in the end, although if your anything like me the end want be for another year because you will keep trying new things with the tune and learning more & more. Cause like they say there is more than one way to skin a cat. Maybe after you master tuning it the normal way you can go down the road of Boost Comp tuning. It is a totally different aproach and works very good for some systems but it is not for the novice to be attemting.

One thing about your whole expeirance is all the trouble you have in the beginning just trying to get the system on its feet. You would of been what , one or two months ahead of the game if it had not been a problem in the beginning, so you would have had alot more tunning under your belt if you had not had to diagnois the system when installing.

It is funny how our wants drive use into new thing. Next it may be a bigger and more effeicaint turbo system, LOL that will be a walk in the park compaired to tunning, and you will already know how to get tuned in for the new turbo setup when you do.

One thing about the GM sensor, they are cheap to go pickup new. If you have a friend with a Auto shop they can be bought at the dealer cheaper than the auto/cheap stores that we normally have to deal with. And ofcourse they are better parts to. Even if you have to just walk in and buy them it will surprize you how competitive priced they are. The dealers
have come al long way with the pricing of sensors.


Jess

[Sam Powell]

When I check this TPS it seems to respond fine. Then when I hook it all up, it works OK for awhile,but goes on the bleep again. What do you suppose is going on here? Do you think the wires are broken under the insulation somewhere? Can this type of TPS fail intermitantly. It seems as if it would not show any voltage if it failed, but the voltage it shows just gets stuck on one value. I don't know how the ECM interprets or uses the feed back it is getting. I don;t know if it is a simple analogue reading or if it uses the change it sees in some digital way. This would explain the "stuck" voltage, so to speak. If it uses it digitaly then maybe if all feedback stopped, it would still register what ever the last voltage was. If it is a simple analogue feed back, then you would think the readout would drop to zero if a wire were broken, or the connectors were faulty.

I hate to just throw parts at it, but I did buy a new TPS. Maybe I should just go ahead and install it even though the old one tests OK. I have had new parts be worse than old ones sometimes. Especially with things like O2 sensors. Also, these infamous GM weather pack connectors do not look as if they make a real secure connection. Anybody know if they are prone to failure?
Sam

_________________
A REAL professional is someone who knows when to hit it with a bigger hammer.

[LUCKY13]

Yea the TPS are bad for doing just what your is doing. That is no garantee that this is the problem but I would threw the new one on there and try it. What happens is the TPS will intermite when going threw temp changes. If it was a bad wire or connection it would read either 0v or 5v or close to those readings.

Jess

[Pierre]

Hmm Sam I've never seen a TPS go bad.. they are fairly simple and only thing that goes past them is air. They usually have seals on them too.

They have 3 pins on them. Resistance is constant between two of them, and varies between the other two pairs. (If we call the pins A B C, resistance is constant between A and C, varies betweeen A and B, and also varies between B and C).

When it gets stuck, if I were you, I'd get an ohm-meter out, unplug sensor from the computer, and check it by hand. You have the new one to compare values to. If it still meets the characteristics above, then its likely not the sensor itself.

I suppose it could be affected by heat somehow, but that seems like a stretch.

[LUCKY13]

[emsvitil]

A TPS usually has one side grounded, and the other side connected to 5V.

The throttle position is determined by the voltage coming out of the center terminal.

If you could tap into the circuit with a voltmeter you can see the voltage vary with throttle position.

Tap into the circuit next to the TPS,

If the voltage varies like it should (doesn't jump around or go high or low) the TPS is probably good and it's the wiring.

I'd then tap into the circuit next to the ECM and see if the results stay the same (confirm the wiring)

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

[slantzilla]

[Pierre]

Was this the first TBI EFI system dodge put on their trucks in the late 80s? Early on in my efi planing I was thinking about using that as a base but strayed away from it as I read about some injector issues.

I'm not doubting that the problem with tps's exist - I'm just having a hard time imagining the failure mode. They are a simple variable resistor - if there was a reaction time problem wouldn't it be due to computer issues?

[dakight]

The resistor film on the TPS wears and collects dirt, kind of like a fuel tank sender, until the resistance calibration is no longer accurate. One fix that I've seen, but have not tried, is to put a capacitor across the contacts on the TPS to take out some of the noise and smooth out the voltage curve. I'm beginning to have some issues with my Dakota that I believe might be related to the TPS but I'm not sure and they are mild and intermittent right now so I haven't really looked into it that much.

_________________
David Kight
'62 Valiant Signet, White
'62 Valiant Signet, Red
'98 Dodge Dakota
'05 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

[Sam Powell]

Thanks for the tips. The old TPS passes the check tests, and the voltage seems to be fine at correct pin. I wondered if the connectors are known for failing. I will put the new TPS on, and search out a new connector, and then proceed with the wiring check as well.
Sam

_________________
A REAL professional is someone who knows when to hit it with a bigger hammer.

[sandy in BC]

Its worth checking the mechanical part of the TPS switch (including throttle linkage) Ive had GM TPS switches stick due to poor geometry of gibbled linkage.

Emsvitils voltage check is bang on the money and easy to do.

Side bar yer Honour! I have had some trouble with bigger cam motors (270 adv duration) "justifying" TPS vs MAP sensor readings. It leads to bog on light throttle acceleration. enriching or advancing spark would seem to be obvious answers but it doesn t work.......

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....


http://www.arrowtipi.com/My%20Webs/index%20Valiant.htm