Hey guys, I made this account to hopefully get help with my truck.

I'll start by saying that I bought this truck for 1400 dollars. It's my new daily driver and I need to get it running right.

The truck has a manual toggle switch to run the truck rich or lean, and the wire for this switch is spliced into the CTS plug.

When the truck is cold, I turn the switch "on" to start it and to warm it up, and it runs the air/fuel mixture rich. When it warms up (time depends on how cold it is outside) I can flip the switch up to a more lean fuel mixture. The temperature gauge does not work (it's at zero).

The problem is that if it is less than ~35 degrees outside, the truck runs terrible no matter how long I warm it up for, and unless its ~60 degrees outside and above, the truck has some dead spots and loss of power.

What I've done so far:

I have used a jumper wire to wire the CTS back to normal, and the truck ran worse than ever before. I have unplugged it all together, and it ran just as bad as with the CTS back to normal.

I've done new wires, plugs, and ran injector cleaner through it for good measure, and tested fuel pressure, and it was fine.

The only other thing I might need to mention is that I have my exhaust coming straight out the cat (exhaust rotted out)

My question is, what do I need to do to get the truck back to normal?

 

It's hard to say exactly what's wrong with it right now, but you mentioned dead spots in the throttle. It's quite possible that you need a TPS - throttle position sensor. Things to check: That your ECT is good (replace it for good measure), your oxygen sensor is working (also a good one to replace), your ignition timing is correct, your cat isn't plugged.

Really, all the fuel control on that truck is controlled by primarily the ECT, oxygen sensor and TPS. Mainly the oxygen sensor. Ideally you'd want to check for codes, and use a scan tool to look at the live data coming from the computer to see which sensors are bad

 

You can read live data off obd1?

 

yessir, GM Tech 1, Snapon Verus/Modis/Solus can all support OB1 scanning and give you live data.

 

Hey NullHead,

So I have a few updates. My brother and his dad are mechanics, but they don't know the parameters of the live data from that truck so pulling live data wouldn't help much.

Anyway, I adjusted the timing on the distrubutor, and it turns out it was actually a bit too retarted, so that helped me a little bit. Also, I replaced the CTS and wired it back to normal. Now, the truck runs worse than ever

The only strange thing is, it runs fine for about 15-30 seconds, but as soon as it enters open circuit fueling, it goes to ****. It will idle fine, and idles where it should, and doesn't die in idle, but actually driving it turns into a nightmare.

I'm starting to think the computer is bad, and I'll tell you why:

1. The wire that you unplug in order to bypass the computer and adjust the timing did not respond, (meaning it was no different plugged in or not) which makes me believe the computer is messed up.

2. The CTS I put in it was brand new, which should correct the problem that made it need to have a fuel toggle switch, but it made it much worse when actually driving. Once the truck warms up though, I can unplug the CTS and it runs perfect.

I'm beyond confused with this thing right now. Also, I forgot to mention that I have no check engine light anymore since I put the new CTS in. It doesn't come on unless I unplug the CTS. Any advice?

Thanks in advance.

 

So does the computer flash code 12 when you jumper the ALDL for codes? If it does flash code 12, the computer should be fine.

I would still suspect the oxygen sensor .. so basically if you're going to scan the computer for live data, look at TPMS, oxygen sensor voltage, CTS voltage, etc.

Consider the oxygen sensor generates voltage when the sensor tip is exposed to gas exhaust gas that does not have oxygen in it, and that the coolant temp sensor changes voltage based on temperature - so when the engine warms up, the voltage changes. If the oxygen sensor is pegged at one voltage and never moves, there's a problem with the sensor or the wiring. The voltage on the oxygen sensor should range from lean (400mv) to rich (700-900mv) and should switch from rich to lean as the computer tries to manage proper stoichiometric burn. The TPMS should range from low voltage to high voltage as you move the accelerator.

So basically you're not looking for good values as much as you're looking for the one that doesn't belong or that doesn't behave as you would expect it to. Also, there will be a field that is labeled "block inegrator" and "block decoder" or something to that effect. That number should be about 128 give or take. That indicates if he computer is commanding rich or lean.