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1989 K5 - Gradual Learning

First 4x4 - learning basic maintenance / upkeep and maybe some small mods.
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I'm thinking you may have issues with the ECM. I chased similar issues with a 88 S-10 Blazer with a 4.3 before I got a hold of a buddy of mine who was a
GM tech. I described everything going on and what I had done. He then told me to access the ECM and while running perform what he called a tap test. The tap test was just giving the ECM a firm couple of taps while the vehicle was running and if changed how it was running as a result of tapping on it the ECM was bad.
 
Drew- if you want to borrow my Tech1 scan tool you are welcome to it. @Bent77 has it currently, but when he's done with it you are certainly welcome to use it.

With it you can actually see some live data like what the map and o2 sensors are doing. It can be helpful in the process for sure.
 
I think I can get an the data I need out of the lap top now that I got it sorted yesterday. It should do the same scans I need
 
Tap test works on gm MAF sensors and Ford duraspark modules also.
Unplugging and re plugging the ECM may help straighten things out.
 
Went outside and took a peek at the MAP. The vacuum line into the TBI unit is fine and the connector looks to be in good shape.

I did a little bit of reading and wanted to ask about testing out my sensors to make sure they're good.

It looks like if I disconnect the sensor (Coolant Temp, MAP) then that is no good. It will essentially read infinite resistance and will cause a ton of fuel to get dumped into the engine. It sounds like I need to do the opposite and short the sensors with a jumper wire.

How is that done? I have some spare wires in my garage... Do I put jumper wires into the prongs of the connectors and then touch the other ends of the wires to bare metal?
 
You know I have a the scanner AND the service manual?
 
Yeah but you're way up there, I'm afraid of driving it to you LOL

EDIT: @Bent77 if you're available tomorrow I may actually try and drive it to you. Text me if so.
 
I've been doing a little bit of reading and am trying to figure out how to test my sensors using a multimeter.

In this old thread, a user named Grinch talked about testing the MAP Sensor with a voltmeter:

"Check the reference voltage supply at pin C of the MAP sensor (gray wire typically). Measure voltage between pin A (ground) and Pin C (+5 V ref) with a DVM. It should be right around 5 Vdc. With Key on engine off the MAP voltage (Pin B, light green wire typically) should read around 4.8 to 4.9 volts. If it reads the same as pin C the sensor is probably is history. Also check ground reference pin A. With everything off, measure resistance between Pin A and electrical ground (stud next thermostat). It should be fractional ohms."

I'm hoping to ask some questions about what he said. I'd tag him here, but he hasn't logged in since 2015 so I doubt he'd be able to help.

1. Check the reference voltage supply at pin C of the MAP sensor (gray wire typically). Measure voltage between pin A (ground) and Pin C (+5 V ref) with a DVM. It should be right around 5 Vdc.
Drew: Is this with key on, engine off?
Drew: I am guessing this is saying to physically put a probe into the MAP Sensor connector, but could he also be saying to supply 5V to the sensor itself and then perform a measurement?

Despite studying Electrical Engineering in college, I am absolute trash with this stuff. That's what I get for never using my degree. I forgot all of it.
 
Yes key on engine off. In the pin b test he has back probed the connector with the sensor plugged in. So red dvom probe in the back of pin cavity B. Open the connector wire insulation retainer part of the plug, a paper clip slid in between the the rubber gasket and the wire will help get the reading.black to ground at t stat.

edit do not supply any voltage. You checking that the computer is supplying voltage, and that the sensor changes the 5 volt reference from the computer. Map sensors create a frequency response the computer is looking for. You could see this with the proper test equipment most folks don't have, oscilloscopes.
 
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Hey guys, not much of a meaningful update but just a wanted to put down some stuff that happened tonight.

I drove the Blazer down I-25 and looped back toward my house. It died a bunch of times while I was slowing down to a stop and I smelled gas frequently. Each time I restarted it, I basically had to floor the gas pedal to get it to start.

Check engine light came on, same codes (32, 33, 45). I shut the truck off and popped the hood and took a look at my injectors. Fuel was bubbling out the top where the electrical connectors are. It was also dripping from the injectors into the throttle plate area of the TBI unit.

After that I disconnected the MAP and tried starting it up again. It behaved the exact same as before and died nearly immediately when I let off the gas pedal.

So here is what I think I know:
-According to this thread and this PDF, disconnecting the MAP will cause fuel delivery to be set based off of the TPS. Disconnecting the MAP made no change to how the truck was behaving, so I am guessing that the MAP Sensor is actually fine.
-Both injectors are new (reman) as of last weekend, so I don't believe they are causing the problem.
-The fuel smell, the excess fuel bubbling out of the injectors, etc makes me think that the IAC likely isn't the problem. In essence if my IAC is having any issue at all then there is something else causing all this excess fuel to get dumped into the TBI.
-According to the PDF that I linked earlier, code 33 being thrown is for the MAP Sensor reporting high manifold pressure (high voltage, low vacuum). If I think that the MAP Sensor is working properly, and I verified that the vacuum line is in good shape, then something else is causing high pressure inside the manifold.

Can anybody think of something that would cause high manifold pressure + excess fuel to be dumped into the TBI? Should I ignore the high manifold pressure for now and just focus on the injectors dumping crazy amounts of fuel into the TBI?
 
You shouldn't have fuel bubbling out anywhere, I think that is a mechanical issue, o rings, or gaskets. Maybe even a crack in the injector tower that holds them.

edit: another thought just came to me has anyone checked your fuel pressure? Could the truck possibly have the wrong pump ? ie high pressure. tbi should be @ 12 to 15 psi
 
Tonight was really great.

Last weekend, I rolled by @Bent77's place and borrowed @ZooMad75's Tech1 scan tool. Tonight I had time to get into the garage and use it.

The first thing I did was double-check my injectors due to @Wes Harden's comment (above). The last time I drove the Blazer, I had fuel bubbling out the top of the injector pods and so after seeing his post I wanted to double-check my o-rings and whatnot. It was a good thing I did because I found a couple of issues.

Here is a pic of my injectors:

PXL_20210624_024313988.jpg

First, one of my small o-rings was a little chewed up:

PXL_20210624_024330702.jpg

Second, when looking at a blown-up diagram of the TBI unit I noticed that I had the metal washer and o-ring (top of first pic) in the wrong order. The o-ring is supposed to go on top of the metal washer, not beneath. I had it installed wrong and got that fixed up.

Once I got all that stuff put back together, I did the Tech1 scan. I used the "Mass Storage Cartridge" and just went through the screens one at a time. I did three separate readings:

-First I went through all of the screens with the key on but the engine off.
-Next I started the engine and had my foot down on the throttle lightly (because I was thinking that it was still flooding and that I had to do that to keep it running). I quickly realized that I didn't need to keep my foot on the pedal anymore.
-Finally I did a third reading with my foot completely off the pedal.

Here is a link to a spreadsheet I made showing the values I got from the Tech1 tool!
https://docs.google.com/spreadsheets/d/1PJEhObI1HYp0VV0Ici-r40anNBX4g_ZLIM-K42SMBnI/edit?usp=sharing

Let me know if you guys see anything weird in the readings.

While I was doing the third reading, I noticed that the Blazer was idling great. So after I completed the third reading I took it for a test drive. It drove great. It didn't flood at stop lights, and it idled more smoothly than ever. It actually was so quiet and calm at idle that I thought it had died.

I am so happy. I don't know if it was the chewed up o-ring and/or the incorrect o-ring/gasket installation that was causing the flooding, but that's the only thing I have changed. I am really hopeful that it's in a good spot now but I am anxious to hear if anyone sees something wrong in the Tech1 scan readings.

THANK YOU THANK YOU THANK YOU THANK YOU THANK YOU to every single person who has ever responded to this thread in the past 5 years.
 
I am glad it is running well now. You did a great job locating the trouble. I for one enjoy helping when and where I can. Get out and enjoy that K5 :waytogo: :burnout:
 
What I see in there:

BLM is way lean, likely because the injector was bleeding around the o ring
Solution: drive it, it will re learn

IAC: this number is pretty high while in closed loop. Typically when warm and off the throttle, the counts should be 30ish, and it will “park” itself somewhere on the 30-70 range when on the throttle
Solution: may need relearned. If it needs 145 counts to idle, we have other things going on. Driving it may push the BLM up and may need less air to idle. Start there

TPS: usually reading .55-.6v on this era tbi. At .7v you’re a tad high. Make sure the throttle is not sticking or intentionally opened. This number may convince the PCM that throttle is being applied and the is parking the IAC since the driver is “controlling the throttle”
Solution: Fix the other stuff first, but see if you can loosen the tps screws and get a lower reading after checking the throttle. You can use the Tech1 and do this without it running
 
Thank you Mark!! I'll drive it around for a bit and will recheck the numbers afterward.
 
Hey all, just wanted to give a quick update. I've been driving the Blazer a lot recently. Overall it is doing great.
  • When I first start it with a cold engine, the idle is rough. However it does not die.
  • Once I drive it around a little bit, the idle smooths out.
  • When the engine is fully warmed up, the idle feels/sounds almost perfect.
  • Only one code has been thrown since my last post, and that is #32 EGR. This code has been there since I bought the truck basically.
I plan to do another Tech1 scan. I was thinking I'll do three tests again:
  1. Key on, engine off. Cold engine.
  2. Engine on, not fully warmed up.
  3. Engine on, fully warmed up.
I'll post the numbers like I did in that other recent post.

Question: Can the Tech1 scanner help diagnose that stupid EGR code? The valve and solenoid are new (~7,000 miles on them).
 
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