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98 Chevy K1500 Z71 - possible vacuum leak or other issue?

Old 06-22-2019, 10:10 PM
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Default 98 Chevy K1500 Z71 - possible vacuum leak or other issue?

Hey all, just bought my first truck today for $1700, and kinda thinking I got screwed on this one and maybe should've walked away. The engine was rebuilt by a previous owner, who also put in a reman tranny and did a lot of other work. However, it runs pretty rough. Seller thinks the big issue is a vacuum leak, and it has sat for a good while, probably also needs a tune up. Just wondering what to check/replace (and I need a good diagram of the engine bay if you have one). My mechanical skills are okay/intermediate/DIY, but I have only worked on my Audi. Here are my problems from the drive home, which was 50 miles:
  • Turns over fine, low RPM idle that eventually stalls.
  • Stalled at just about every stop/red light.
  • Rough, slow accel most of the time, but occasionally good throttle with more gas.
  • Accel pedal sometimes seemed unresponsive
  • Light acceleration I got a grinding noise.
  • 50 mile trip, avg 55mph 10 MPG.

Other problems that might be related:
  • Has 4x4 options, but the front drive shaft is not installed. I drive it in 2wd back home.
  • Passkey/Security issue - I can only start it in overdrive to bypass (Steering column from Yukon was put in)
  • Dash instrument cluster - nothing except the battery gauge and occasionally the tachy work. All lights were on during the trip back, but seemed to turn off when I was tinkering at home.
  • Battery pretty low voltage - I killed it tinkering in my driveway... gotta charge it somehow now.

Please help!
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Old 06-22-2019, 10:21 PM
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After 5:14 in that video, that is pretty close to the grinding sound I mentioned.
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Old 06-23-2019, 09:44 AM
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I would start with your system voltage first. This can cause run ability issues with the HV ignition system.
Check for any codes. Even pending ones are a good start.
I would verify your timing is correctly set.
PASSKEY isn't the issue. This is just a matter of installing the correct shifter.
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Old 06-23-2019, 01:55 PM
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Battery voltage is about 8v right now. Not sure if it'* still under warranty. It'* Interstate and there aren't any markings. Going to Autozone to pick up a scanner and PCV valve and some other things. Will take it to have it tested and confirm.
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Old 06-23-2019, 03:25 PM
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Is that 8v running or off?
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Old 06-23-2019, 03:38 PM
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Only accessories were running. Took it to auto one they said it was completely bad. I got a new battery. Now instrument cluster appears to be working except oil and temp. Still idling low. Got P0452 codes and some abs codes too.
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Old 06-23-2019, 03:52 PM
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Engine is turning over, but doesn't start now. I did get it started once. Seems to idle ok for a minute around 1000RPM, then drops to around 500RPM and runs pretty rough. I need to take a look at the gas tank when it'* not raining out. The gas cap didn't look to good the last time I refilled it. Guessing it could be other things - including vac leak.
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Old 06-24-2019, 03:17 PM
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Changed the oil this morning and replaced PCV. Got it running and drove around the block. Cleaned the spectre air filter and air drying it now. When I put my hand over the air intake where the filter goes, that seems to correct the idling when it drops. So I'm guessing that it definitely is a vacuum leak, or maybe a sensor fail.

So if the Passkey Secure issue isn't resolved, should the instrument panel function properly anyway? I am thinking about replacing that or checking for cracked solder.
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Old 06-24-2019, 05:09 PM
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Passkey would only disable the starter I think.
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Old 06-24-2019, 05:10 PM
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What is your current system voltage?
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