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post #1 of (permalink) Old 07-29-2000, 03:06 PM
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Check engine light

Is there any way to find out the trouble codeson the blazer without hooking the truck up to a scanner? I know with my toy and nissan I can get the codes by reading the flashing lights on the computer.

Theres definately something wrong with this truck, its constantly stalling. I put new plugs, wires, cap and Roter. Is there some magic trick to timing this fuel infected truck, or would it be the same as doing my 68 Oldsmobuble?


JAG
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<font color=red> 90 X-Cab Toyota V6 5Speed, 4 inch procomp, 3 inch DC, 35x 12.50 BFG Baja's.[img]/wwwthreads_images/icons/cool.gif[/img]
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post #2 of (permalink) Old 07-29-2000, 07:40 PM
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Re: Check engine light

Usually, pins "A" and "B" of the ALDL need to be shorted together with the ignition switch in the "ON" position to get the "Service Engine Soon" or "Check Engine" light to start flashing. Usually pins "A" and "B" of the ALDL need to be shorted together with the engine running to check/set the timing. Just make sure you know what the pins are of your ALDL, short the wrong pins together and your going to have lots of fried stuff!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Once pins A&B are shorted together, with the ignition switch on, the check engine/service engine soon light will flash once, "a 1" then a moment later flash twice "a 2". The computer will flash "1", "2" three times, then the trouble code will start to flash. For example if you get three flashes "3" then two flashes "2" you have a trouble code "3" "2". The trouble code "3" "2" will flash three times. If there are more codes then that code will be flashed. When all codes are done flashing, then the computer will flash "1" "2" again at the end of all the trouble codes. If all you see are codes "1" "2" you have no faults.
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post #3 of (permalink) Old 07-30-2000, 01:48 AM
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Re: Check engine light

Thanks Dave.

I ended up just just running that screw on TBI in a little to rev the motor slightly higher (didnt think there was an idle adj. so im not sure thats what it was, it basically pushed against the throttle arm) its basically compensating for the problem for now. but id like to figure out whats wrong with the thing. Its constantly stalling at idle while in gear and and if you give it to much gas it hesatates and takes a while to get up an go. I mested with the timing and it seemed to help, but the wierd thing is when I tried to time it, the mark on the balencer was at 10* when I started, now its running a little better and its off the scale, about at where 15-16 would be, on the before side. The sticker on the truck says its supposed to be at 0* . I didnt have a consistant check engine light before hand, but after I got out of the shop and home, it was on, and if im getting the code right, its a 21, (grounded WOT circuit or TPS circuit) I dont even know what a WOT is, and I have know idea what to do with a TPS. Any ideas? Im getting really frustrated.

Appreciate any help, thanks.

JAG
Las Vegas NV

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<font color=red> 87 K5 Blazer Silverado Bone stock. The womans ride.
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post #4 of (permalink) Old 07-31-2000, 01:07 AM
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Re: Check engine light

Well, here is a book answer ("Motorbooks International" How to Tune and Modify Chevrolet Fuel Injection by Ben Watson ISBN# 0-7603-0422-X) . Code 21 denotes Throttle Position Sensor (TPS) voltage high. The code occurs if the ECM sees a signal above 2.5 volts from the TPS while the Manifold Absolute Pressure (MAP) sensor is sending a signal indicating a pressure less than 8.25 psi in the intake manifold. The pressure would equate to a manifold vacuum of greater than 16.75 inches. Additionally, the engine RPM may need to be less than 1,600. These three conditions must be met for 2 to 5 seconds.

Typically, a Code 21 well be set when there is a defective TPS, when the black ground wire running from the TPS to the ECM has an open circuit, or when the dark blue TPS signal wire is shorted to voltage. Check for these three problems.

Now what does this really mean. It means that the Throttle Position Sensor could be bad. It could mean that one of the wires to the Throttle Position Sensor could be bad.
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