1989 K5 - Gradual Learning

[ZooMad75]

When Drew came by to pick up the Tech1 I fogged the piss out of the engine with brake clean looking for a vacuum leak. Zero blips of the idle speed at all. I fogged the base of the TBI unit looking for a leak at the throttle shaft, base plate gasket, and zero change. I don't think it has a vacuum leak.

 

[shima]

Do you guys think this throttle shaft bore wear is all that bad? It doesn't seem like a lot of play to me but I did a test where I checked the TPS voltage after hitting the throttle a number of times. Apparently the TPS voltage is supposed to come down to the same value over and over after you let off the throttle and when I did the test it settled down to a variety of values.

I zoom in at about 30 seconds in the video in case it is hard to see at first:

View attachment PXL_20230817_003904224.mp4

EDIT: I don't actually know if I am checking for wear correctly. Ooof.

 

[ZooMad75]

If the throttle shaft bores were loose you’d have a vacuum leak. We would have noticed a change in idle speed when we sprayed brake cleaner all over it.

I guess it could be slightly loose that it doesn’t leak vacuum but cause your tps value to jump around.

 

[Wes Harden]

There could be dirt ring built up at the throttle blades, messing with your minimum ai setting.

 

[shima]

@ZooMad75 and @Wes Harden my TPS voltage when I first started the Blazer was 0.7V. I hit the gas and then let off the pedal. It came back down to 0.74V. Then I did it a couple more times... it came down to 0.74V and then 0.8V.

My question is, could 0.1V total difference (0.7 - 0.8) really cause such a problem? Maybe the voltage is just too high (Eagle Mark thread said 0.54V is normal)?

EDIT: My idle RPM is 1000 which seems really high. Maybe I should just focus on that before going down the TPS rabbit hole. I feel like I'm all over the place.

 

[Wes Harden]

those voltages don't bother me. TPS is potentiometer, any change in resistance will effect the voltage reading. little dirt a little heat, will change the reading.
I think the minimum is worth looking at, be sure the throttle bore is clean at the butterfly. check the injector spray pattern nice smooth cone curtain. No dirps drops or gaps.
the spark plug color shows your air fuel ratio is pretty good, so that brings us back to minimum air.

 

[shima]

Alright, I have some updates...

• Minimum air - the factory "plug" that blocks the throttle body torx screw is still in place on my unit. This makes me think that the torx is still at the factory setting and that I shouldn't have to adjust it.
• TPS - we're seeing a small variance in voltage readings, but the TPS reliably comes back down to a stable level after letting off the throttle. It climbs steadily as the throttle moves through its stroke.
• IAC - I drove around with the Tech 1 yesterday and watched the IAC counts. I found this tremendously helpful article and finally understood what the counts meant. When my engine was fully warm, the counts were hovering between 75-95. This was while I was in Park. The article states that it should be between 20-50.

Okay, so my IAC counts are high. The IAC is letting in more air than it should.

The article that I linked earlier has these possible causes listed:

Now if you see the scan data reporting IAC position higher than 20-50 counts on a fully warmed up engine, this could indicate one or more of the following problems exist:

1. There is carbon buildup on the IAC pintle, or in the idle air passage restricting air flow
2. There is carbon buildup on the throttle blade or throttle body bore
3. The throttle stop screw is adjusted incorrectly (throttle resting closed too much)
4. There is a mechanical problem with the engine resulting in lower than expected vacuum levels at idle (this will require the IAC to open further so the engine gets the required amount of air to maintain the preset idle speed)
5. There is increased load on the engine (such as what would occur if the automatic transmission was shifted into gear)
6. The IAC valve itself is faulty

Given what I know about my Blazer and about all of the stuff involved with this problem... I narrowed it down to items 1, 2, and 6.

When I got home from the drive, I cleaned the absolute shit out of my throttle body and installed a new IAC from O'Reilly. Tonight is the first test drive. I am going to do the reset procedure and drive around for a while to get the temp up. Then I'm going to watch the IAC counts and see what happens. I have heard that it may take a few key cycles for the IAC to "learn", so I am going to try and give the truck a few test drives before making my next decision.

I am optimistic that I'm on the right track. @ZooMad75 called out that I could need a new IAC on July 5th... nearly two months ago. I was resistant to it because I replaced the damn thing in September of 2020 (7500 miles ago). We shall see.

Thanks for everyone's help, and I'll keep you guys updated.

 

[Wes Harden]

Was the throttle bore at the blades very dirty ?

While having the min air screw still plugged is good thing meaning no one has messed with it, it could still need a little tweak, after all is said and done. The screw is just a stop for the throttle linkage. Over the years of the linkage banging back into it might be slight blunting of the end and shorter then when new.
If you feel more is needed after road test, don't rule out this adjustment. Follow the procedure and it won't do any harm.

 

[shima]

Was the throttle bore at the blades very dirty ?

A little bit, but not to the level where it would block the blades in some way.

While having the min air screw still plugged is good thing meaning no one has messed with it, it could still need a little tweak, after all is said and done. The screw is just a stop for the throttle linkage. Over the years of the linkage banging back into it might be slight blunting of the end and shorter then when new.
If you feel more is needed after road test, don't rule out this adjustment. Follow the procedure and it won't do any harm.

I appreciate that comment. My torx screw is definitely blunt. I could feel it on the back end with my finger tip.

 

[shima]

Last night on the first test drive, my IAC counts were pegged at 145. While parked I revved the motor up to monitor my O2 sensors and I noticed that the IAC counts dropped the slightest bit (down to like 141). Obviously the stumble was still there... but it didn't die on me or anything like that.

I am trying to not get discouraged, I know it may take a few key cycles to finish "learning".

RE: The O2 sensors... I'm trying not to get distracted... but the stated acceptable range is like 100mV - 900mV. Mine were dropping down to single digits (~4 mV) quite commonly. The highest they got was perhaps 750mV. I am ignoring that until I complete a few more test drives.

 

[82355]

You only have one O2 sensor.

Martin

 

[Blue85]

At 1000RPM idle speed, it's getting plenty of air. Too much, really. This could be a stuck EGR if the brake clean test passes, but I thought that had already been eliminated. The MAP goes from 0V at 3"Hg to 5V at 1ATM (30"Hg) so 1V is like 20% load on the engine. These two things could be related (too much air reduces vacuum). If the IAC is moving, that means the engine is seeking 1000RPM, which would mean somebody has changed that setting in the ECM.

The IAC is a stepper motor and the ECM counts how many times the coils have been pulsed (each pulse is 1/4 turn). It doesn't know if the valve actually moves or not. (On newer cars there is a feedback so the actual position is known, so it's easy to confuse this.) Having the same idle speed at 12 counts and 61 counts suggests that it is not moving. One way to test it is to turn the valve by hand and reinstall with it unplugged to see if idle speed is changing. You should also be able to see it move by taking it out, leaving it plugged in and turning the key on (most ECMs will "push out" a bunch of counts to bottom the valve, then "back up" the indicated number to get to the desired setting).

You'll have to get that idle down to 750 or so (in P) to know if it's running right. What's the idle speed spec on the emissions sticker? But what are the odds it's always at exactly 1000?

 

[Blue85]

RE: The O2 sensors... I'm trying not to get distracted... but the stated acceptable range is like 100mV - 900mV. Mine were dropping down to single digits (~4 mV) quite commonly. The highest they got was perhaps 750mV. I am ignoring that until I complete a few more test drives.

Can you display the O2 on a graph? The absolute voltages don't really matter, but it should be sharply transitioning well above 0.5V and well below 0.5V and often.

Something like the red:

 

[ZooMad75]

He’s got my tech1 scan tool. So no graphing ability. Just have to watch the voltages. But I agree it’s more that it’s switching hi/low more than what the actual numbers are.

 

[shima]

@Blue85 thanks for the response! I really appreciate you taking the time to try and help me out.

At 1000RPM idle speed, it's getting plenty of air. Too much, really. This could be a stuck EGR if the brake clean test passes, but I thought that had already been eliminated.

I believe the 1000RPM idle speed is actually related to the diagnostic test that I was doing on the Tech 1 scan tool. I did another test today (more on that later) and noticed the RPM jumped when I selected the "Diagnostic Test (10k)" option. I never knew what 10k was until this morning... I think it raises the RPM to that value artificially. Yep, we tested thoroughly for vacuum leaks and my EGR valve is plugged anyhow.

The IAC is a stepper motor and the ECM counts how many times the coils have been pulsed (each pulse is 1/4 turn). It doesn't know if the valve actually moves or not. (On newer cars there is a feedback so the actual position is known, so it's easy to confuse this.) Having the same idle speed at 12 counts and 61 counts suggests that it is not moving. One way to test it is to turn the valve by hand and reinstall with it unplugged to see if idle speed is changing. You should also be able to see it move by taking it out, leaving it plugged in and turning the key on (most ECMs will "push out" a bunch of counts to bottom the valve, then "back up" the indicated number to get to the desired setting).

So the "counts" value I see with the Tech 1 scan tool is how many times the stepper motor has been pulsed by the ECM? If this is the case, do pulses to the stepper motor retract the pindle? I am confused on this because I thought the IAC is meant to open and close many times throughout the drive cycle... and if that's the case, it seems like the "counts" value would be useless. I am probably not getting it.

You'll have to get that idle down to 750 or so (in P) to know if it's running right. What's the idle speed spec on the emissions sticker? But what are the odds it's always at exactly 1000?

I did another test drive today and used the "road test" option on the Tech 1 instead of the "diagnostic test". I still need to read the manual, but it appears that the only difference between the two is that the road test does not artificially bump up the RPM. My idle RPM is wayyyyyyyyy lower now.

Today's test drive situation:

• Drove ten minutes north on I-25, shut the truck off.
• Helped my girlfriend for five minutes.
• Drove ten minutes south on I-25, parked in front of my house. Kept the truck running in Park.
• Took a reading on the Tech 1.

Here were the readings:

• Temp: 187 F
• MAP: 1.6 Volts (~25% load on the engine - is that normal in Park?)
• TPS: 0.62 Volts (went down to 0.60 Volts on its own, then back to 0.62).
• Rich/Lean and O2 Cross Counts: Went from Lean (20) to Rich (10).
• Engine Speed: 525 RPM
• INT / Block: 117 / 108
• IAC: 20 (Finally a "normal" IAC reading!!!)
• O2 Sensor: Not oscillating all that well (YouTube Link)

That idle seems way too low for Park. Unless you guys see anything crazy, it looks like everything else is somewhat normal. I am curious what you guys think about the oxygen sensor reading.

I am at the point of thinking that perhaps I should mess with the minimum air screw a little bit and just retest to see how it behaves. I can always back the screw out again. I have this weird sadness about doing it because it is unmolested but if @Wes Harden is right and the screw has just been worn down over the last 30 years... it may really be the right fix.

 

[Blue85]

IAC "counts" goes up and down as the pintle is commanded to retract and extend. So one way adds to the number and the other subtracts. It's an indication of how far the valve is from full closed. Like I said before, there are times where the number can get off, but it resets every time you start the engine.

 

[Wes Harden]

o2 sensor is a chemical battery it make milli volts in the presence of oxygen. They get used up and slow way down before they quit. It may be time to get a new one. If you have leaks up stream of o2 this mess with the accuracy of the o2 sensor.

I am suspicious of the map sensor and the egr. The Map may be dirty and not reading accurately, or have a small leak in line to it. The egr valve itself can leak exhaust gasses into the intake, weather or not the control line is plugged. While your truck is warmed up and idling give the egr valve a love tap with soft face hammer, and see if the idle changes.

How was the drivablity and restarting on today road test ? Sound like it started good and drove well no attempts to stall ?

 

[shima]

o2 sensor is a chemical battery it make milli volts in the presence of oxygen. They get used up and slow way down before they quit. It may be time to get a new one. If you have leaks up stream of o2 this mess with the accuracy of the o2 sensor.

I am suspicious of the map sensor and the egr. The Map may be dirty and not reading accurately, or have a small leak in line to it. The egr valve itself can leak exhaust gasses into the intake, weather or not the control line is plugged. While your truck is warmed up and idling give the egr valve a love tap with soft face hammer, and see if the idle changes.

How was the drivablity and restarting on today road test ? Sound like it started good and drove well no attempts to stall ?

Thanks Wes. I'll take a peek at the MAP tonight and will also smack the EGR. I'll be working on it in the garage for the next few hours.

Initial startup when cold, it fired off and died. Had to give it a little pedal to get it started up and idling. Driveability was fine, but the shake was back by the time I took the reading at home.

 

[shima]

My friends I have some updates. It has been an eventful 48 hours. Bear with me while I tell a little bit of a story.

Saturday night:

• Looked over a few things in the garage:
  • Double-checked the vacuum line to the MAP. Pulled the MAP off and tried to figure out if I could clean it or anything like that. Figured that there was no way to really clean it and hooked it back up.
  • Warmed the Blazer up and smacked the EGR with a dead blow. No obvious change in idle, but it was sort of hard to tell because the stumble is a bit hard to hear while the Blazer is in park.
  • Double-checked my injector spray pattern. Driver-side injector was spraying a clean cone but also looked to be dribbling fuel a little bit.
• Took it for a test drive with the Tech 1 hooked up:
  • All of the readings looked fairly normal at first.
  • The stumble was pretty bad. I started to feel it even while driving around town, which was disappointing.
  • I called @ZooMad75 while I was driving and we came to the agreement that I should put a can of BG 44k into the tank and re-evaluate.
  • While on my way to AutoZone to buy fuel system cleaner, I floored it while on I-25 and noticed that the MAP reading stayed high. We expected it to drop when the throttle was opened. Rob and I agreed that I should probably just pick up a MAP if I could because they're cheap and easy to replace.
• Came up empty-handed at the parts store:
  • They don't sell BG 44k and did not have a MAP in stock.
  • Tried to start the Blazer to head home and it wouldn't start. Crank no start condition.
  • Called my girlfriend to pick me up, went home and grabbed tools, and tried to figure out what was going on.
  • Confirmed fuel and spark. Heavy fuel smell. Figured it was flooded. Disconnected the injectors and was able to start it with my foot on the floor. It ran for about 5-10 seconds and then died.
  • Reconnected the injectors and tried again, still would not start. Crank no start condition. I got pissed and gave up. Girlfriend and I went home and left the Blazer in the parking lot.

Sunday night:

• Came back to the Blazer and looked it over fresh:
  • Found that the damn ECM I fuse was blown. It must have blown while I was trying to get the Blazer to start the night before.
  • Replaced the ECM I fuse and tried again. It started but ran like shit and quickly died.
  • One of the guys from AutoZone came out and checked on me. He watched the injectors while I cranked. Only one of the two injectors was spraying fuel. Driver's side injector was not spraying at all.
  • I tried smacking the injector pod while cranking. No go. I was an idiot and I accidentally hit the connectors and broke them.
  • I used a voltmeter to confirm voltage at both connectors with key on. I also swapped the connectors and put the "good side" connector on the bad injector. Still no go. Decided that the driver's side injector had truly died.
• Mulled over options:
  • New AC Delco injectors were available way up north in Northglenn (~$230 each), but the connectors were not available anywhere in town. The same AC Delco injectors were available on RockAuto for about half the price and obviously RockAuto has the connectors.
  • I decide to get the Blazer towed home. Called a local tow company and they quoted me $130. I figured that I was saving that much money and more by getting the parts online.
  • After booking the tow, I realized that I should call my friends and see if anyone knew of someone who could help me out. I called Rob first and he immediately volunteered to drive down from Arvada and tow me home with a rope.
• Hung out with Rob and got going on ordering parts:
  • We put the Blazer into neutral and he pulled me with the S10 back home. It went flawlessly and I was tremendously thankful - he saved me a boatload of cash.
  • I took Rob out for a couple of beers to say thanks and we parted ways after some great conversation.
  • New AC Delco injectors and connectors on order from RockAuto. Should be here on Wednesday.

If you're still reading after all of that, I appreciate it. Here is what we're thinking for root cause...

My injector connector wires on the driver's side were in really bad shape prior to all of this. They have been in bad shape for years. Pinched in a few areas, wrapped in electrical tape due to exposed wire, etc. I think I pinched them again just in the last week from removing and reinstalling the air cleaner so many times. Through all of that abuse, it is possible that some of the wire strands inside the coating were broken. Those weakened wires trying to carry enough current for the injector could have led to the injector being fried up.

I replaced my injectors shortly after @Capt Ron came over back in May of 2021. They only have 7,000 miles on them. However, I pinched the shit out of those driver's side connector wires back in June of 2020. I wrapped them with electrical tape to cover the exposed wire and moved on. Carrying on with those weakened wires might have contributed to the short life for the injector. Also I bought reman injectors instead of new, so perhaps they were just poor quality. I'm going to get this new stuff installed and see where that gets me.

A massive thanks to Rob and to everyone else who has responded on my thread. I can't overstate it. It's wild to me that you guys help me out with my stupid questions, ask for nothing in return, and then come and help me out when I'm in a pinch. I appreciate it and hope that I can help someone else out down the line.

 

[shima]

I spent Labor Day weekend on a trip with some friends. Had a good time and tried not to worry much about the Blazer.

One of the downsides of living in the city is that the street sweeper rolls through each month. It's a $50 ticket (maybe $75?) if you don't move your car out of the way. I got back from the trip on Monday afternoon and told myself that I could get the new parts installed in time. The sweeper comes through today.

When installing the new injectors last night, I over-tightened one of the throttle body bolts and broke the damn throttle body.



It was one of those moments where I just had to walk away and call it a night.

I taped a note on the inside of my window asking for the street sweeper to show me mercy. We all know that ain't gonna work, but it is worth a try.

I have two questions for the CK5 community:

1. Does anybody know the gauge of the injector connector wires? I was using red 22 ga crimp connectors, and they kept slipping off. Really want to make sure I have a secure connection and couldn't find the info online.
2. Does anybody have a TBI throttle body for sale? lol

I'll put a post out on the Parts Wanted forum for #2.