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350 TBI Possible Intake Leak?

shima

shima

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Hey all, my '89 K5 is having some odd issues recently... hoping to ask for your input and advice.

Symptoms:
  1. Feels as though it is pulling forward even when I do not have my foot on the gas. Feels like it fights me when I am actively hitting the brake, like it does not want to shift down through the gears.
  2. Once the engine is warmed up, engine idles really rough when in Drive and at a stop. Sitting at a stoplight or whatever you can feel it in the driver's seat, the whole thing vibrates on and off. Seems to go away when you put it into Park.
  3. RPMs in Park sound really high, but I don't have a tachometer so I don't know for sure.
  4. After driving for a while, if you shut off the truck and start it up again, Check Engine light sometimes comes on and top speed is SUPER LOW. You will rev the engine and it won't shift up to a higher gear. I don't know if these trucks have "limp mode" but that sounds like a good description of it. Makes me think it is overheating. My temp gauge doesn't work so I don't know for sure. Let it sit an hour and come back and you can drive it again fine.
Anyhow, I have a Haynes Fuel Injection manual and in there it says uneven idle while hot could be an intake leak. Makes sense to me, more air coming in than expected throws off the fuel/air mixture and causes everything to get real hot real fast. Just thinking out loud. Let me know if anyone has any thoughts or things to check out.

THANK YOU as always, I appreciate you guys and gals.
 
vacuum leak. make sure all your hoses are good look down the TBI unit w/o air cleaner and open throttle, engine off, look for black gasket material sticking out into throttle bore. If you don't see anything there, snug down the 3 13mm head bolts on the TBI.
 
Wes Harden said:
vacuum leak. make sure all your hoses are good look down the TBI unit w/o air cleaner and open throttle, engine off, look for black gasket material sticking out into throttle bore. If you don't see anything there, snug down the 3 13mm head bolts on the TBI.
Click to expand...

Heck yeah thank you @Wes Harden!! I'll give these steps a try tomorrow and will report back after a test drive. I appreciate you man.
 
Spray carb cleaner around the intake gasket and hoses. If the rpm’s increase then you have a leak.

You need to check your codes which can be done with a paper clip. Codes get stored for 50 start/stop cycles or unless the battery is removed. And obviously you need to get your temp gauge working.
 
rampage said:
Spray carb cleaner around the intake gasket and hoses. If the rpm’s increase then you have a leak.

You need to check your codes which can be done with a paper clip. Codes get stored for 50 start/stop cycles or unless the battery is removed. And obviously you need to get your temp gauge working.
Click to expand...

Agreed on all fronts. I made the mistake of purchasing a code reader, which is probably just a paper clip wrapped in plastic. The only codes shown are 32 and 43, which have been around a long time. Not to hand-wave them away or anything, I am just used to seeing them.

Does "limp mode" exist on these trucks? Does it occur after the engine overheats? I have always suspected my temp gauge was not working, but that would finally prove it.
 
Yes limp mode exists on your 89. But you need to fix the two codes before anything else. I’d have to spend a few mins to look them up and figure out what they mean.
 
32 is an EGR code and 43 is electronic spark timing control. I have been dragging my feet on them ever since I got the K30. @Wes Harden gave me an excellent diagnostic test a while back which involved testing pressure within my exhaust. The theory is that my cat is clogged. Haven't done it yet, probably should jump into that ASAP.
 
Call me later, have a few tidbits that are easier to explain that way
 
You can also measure the temp of the inlet and outlet of the cat with an infrared thermometer (free to rent at an auto parts store). Google it and you’ll find what the temp difference is to indicate a plugged cat.
 
Code 43 pops up a lot when there’s knock detected or the system can’t perform the knock test. I forget which one of them it is.
 
code 43 and 32 maybe linked. If the egr is not flowing, for what ever reason, when the EST( electronic spark timing) does it self test code 43 will set.
3 things from when I worked on these the sensors are not very accurate, there is a specific torque spec. If to tight or loose the accuracy off.
the connectors get damaged easily. I think this code is way gm invented Top Engine Clean. you may want to Sea foam your pistons.

but i don't think that is your immediate issue with the fast and poor idle symptoms. Vacuum leak will cause these, also if temp is up engine will run fast, an attempt to cool down. Does it idle normal when cold ?
 
I forgot trouble shoot code 32 first, and fix. code 43 may be solved at same time.
 
I got out there tonight and looked over everything. Took me way longer to check it out than I thought, sorry about that.

Despite my embarrassment I have to admit that I think this "vacuum leak" was self-inflicted... and I don't think that I have a vacuum leak at all.
  • I took off the air cleaner and looked down into the throttle bore with a pole pushing the gas pedal down. Couldn't see any gasket material, it looked clean in there.
  • I snugged up the three 13mm bolts on the throttle body. They were snug already but I tightened them a bit further.
  • I started up the Blazer without the air cleaner on and I sprayed every hose I could find connected to the throttle body. I think I counted four of them total, all on the front side of the throttle body. Did not hear any change in RPM.
Then I saw this f***ing thing (circled in green). This photo is not of my truck, forgot to take photos tonight.

2433e87b1612cdb19a5f12007a9e19bf.jpg

I remembered that I messed with that thing a while ago. It's the hook thing that you can spin clockwise or counterclockwise and it limits how far back the throttle plates sit when your foot is off the pedal. When I messed with it I would have sworn I put it back exactly where it was beforehand but I guess I was one half turn off. I loosened it one half turn and it helped out a LOT. Less stuttering, less pulling.

There is still a small amount of stuttering at idle. It is also still pretty bad when I put the truck into reverse. But it is light years better than it was. I might loosen it one more half turn just to see what happens / how it drives.

I think after going through the steps I bulleted above I can say that I don't have a vacuum leak... I just screwed something up and didn't put it back correctly!
 
the computer tried to compensate for the miss adjusted throttle linkage. it may take a drive or two for it adjust back. you do want just a little bit of back and forth, between the linkage post and the cable end.
 
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