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katmat
07-26-2009, 08:17 PM
I posted last week about my 1997 205 w/ a 5.7 fuel injected engine. The engine idles at about 1800 rpm's & the check engine light is on. I checked for codes & code 22 comes up (throttle position sensor). I have replace the sensor but it still does the same thing. I checked the voltage at the sensor & it was 1 volt regardless of the throttle position. Unplugging the sensor doesn' change the engine speed.
Is there a way to adjust the voltage?
Does it sound like a bad ECM? If so am I able to buy one of these? A dealer told be they are about $1,300.00.
Any ideas?
Thanks,
Matt Murphy

JimN
07-26-2009, 08:47 PM
Look for the same color wire at the ECM but also, measure the resistance from the TPS plug to the MAP sensor plug- they share their ground. Your code indicates high TPS voltage and code 21 is TPS voltage low. Which wire were you checking- DO NOT pierce the insulation when checking voltages. The gray wire should have almost 5VDC on it when the key is ON or the motor is running. The Blue wire is the return to the ECM and if you measure the voltage coming out of the TPS, you should see a range from .7VDC - 4.7VDC (approximately). If the gray wire has less, measure at the ECM by removing the plastic caps on the large plugs (they're marked J1 and J2).

Don't replace anything until you measure voltages, resistance and sensors. If you want to find out whether the ECM is bad or not, the wrong way is to buy one and try it. The right way is to have the dealer check it by connecting it to the diagnostic computer and checking it out. If they don't have this, find a new dealer. The sensor voltages can be seen when connected this way and this is the real way to diagnose this stuff, not by just replacing parts.

If you have a good GM dealer who sells, installs and services GM Performance Parts crate motors and you don't have a MC dealer nearby, the GM dealer can check the ECM, too. GM Performance Parts use the same ECM, or they did for quite a while.

boyd
07-26-2009, 09:49 PM
Good job Jim,

That's exactly what I was thinking.

katmat
08-02-2009, 08:51 PM
Thanks for your help Jim!
I started checking the voltage as you said. It looked like the new (2 weeks old) TPS was also bad, so I checked it with a ohm meter & it was open (the original one had a little resistance). So I went to the marina (MC dealer) & explained it to the owner, who also is the mechanic. He agreed the new one was bad but he didn't want to give me a new one. After some discussion he finally give me a new one which I checked for resistance before I left.
Put the new one in the boat & it runs great!
When I purchased the new TPS from the marina I paid $130.00 (The marina said they don't set the price)!!!
Went to a local Napa parts store yesterday & we did a little research & they can get it for $31.00. (my boat is a 1997 & the chevy part is for a 1994 chevy).

Thanks again for your help.
Matt Murphy

chico
08-02-2009, 09:47 PM
when you need an engine part just specify a 1994 c1500 chevy pickup with a tbI 350

JimN
08-02-2009, 10:04 PM
Thanks for your help Jim!
I started checking the voltage as you said. It looked like the new (2 weeks old) TPS was also bad, so I checked it with a ohm meter & it was open (the original one had a little resistance). So I went to the marina (MC dealer) & explained it to the owner, who also is the mechanic. He agreed the new one was bad but he didn't want to give me a new one. After some discussion he finally give me a new one which I checked for resistance before I left.
Put the new one in the boat & it runs great!
When I purchased the new TPS from the marina I paid $130.00 (The marina said they don't set the price)!!!
Went to a local Napa parts store yesterday & we did a little research & they can get it for $31.00. (my boat is a 1997 & the chevy part is for a 1994 chevy).

Thanks again for your help.
Matt Murphy

If they don't set the price, who the he!! does? Glad to see you got it working.