89 K5 w/3" Exhaust...and Issues

[Lov-2-Rev]

Hi everyone! New to the forum, but not to the box style GM's.

Not long ago I purchased a mostly stock 89 Blazer as a non-runner and missing a majority of the parts forward of the rad. Previous owner made a bit of a mess out of the front end (including wiring) while attempting a single headlight nose swap. Fortunately, he didn't know enough or own it long enough to do any real damage.
Sooo, I sourced a complete 89 nose from my local Craigslist and poured over engine bay wiring schematics, and voilà! I have a running, rust free AZ K5 in my driveway! (something to brag about here in the north east)

On to my next issue left from the PO...exhaust. Or lack of. The truck came with long tube headers that had 3" "Pypes" brand mufflers band-clamped onto them...that's it.
I deceided that a single 3" Flowmaster exhaust with a 50 series muffler would do nicely. So I had a local muffler shop fab up a custom Y-pipe to connect the headers to the rest. Also had them install an O2 sensor and bung in the driver side collector seeing as there was none.
Got to take it out on its first real test drive this evening (besides around-the-neighborhood test runs). It runs decent and drives good. Sounds great!
I warmed it up for about 5 mins before leaving. At first, it had a tendency to load up or stumble a bit while cruising at light throttle. Once it started coming up to temp it seamed to run smoother. Then after 3 or 4 miles, the "Choke" light on the dash came on (gauge cluster was swapped along the line) and it began stumbling again. But under moderate throttle, it runs pretty darn good.
So I shut it off and restarted it. Dash light turned off but it continued to stumble at light throttle.

Can anyone lend any suggestions on how to solve this issue?

Thanks, Jesse

 

[riflerk20]

an 89 shouldnt have a choke choke light, it should be injected unless a carb was swapped in it.
if it does have a carb is the choke open once its warmed up?

 

[dyeager535]

I'm guessing the choke light is now the "check engine" light since he mentions O2 sensor.

If you can get the code to come back (or even if not, can't recall if/how they store codes on those ECM's) check it. If you don't know how to check codes, google "paperclip code reading GM OBD1" and you should get some results. Pretty darn easy. That SHOULD point you to an area of concern, check it out.

Realistically on the TBI rigs you'll want an ALDL cable, laptop, and tunerpro RT for diagnostic purposes, but not necessarily a requirement.

First check should be a very good underhood inspection to make sure something didn't get knocked loose, disconnected, broken, etc., then once you are good there, make sure the "check engine" light operates properly before and after you start the rig. Should illuminate and stay lit with key on, engine off, then go off as soon as the truck starts.

 

[Lov-2-Rev]

Thanks for the responses!
As I mentioned, the gauge cluster was swapped out; For an earlier one with the factory clock. I'm assuming that the "choke" light is acting as the check engine circuit.
I've sorted out everything under the hood and verified that everything under the dash is in order.

When I turn the key to the on position(not running) the light doesn't come on. Only after driving it for a while does the light come on.

I'll give the code reading trick a try!

 

[Lov-2-Rev]

Correction:
The choke/check engine light does come on with the key at on position. Checked the flashes and got a code 14 & 15. Which are both coolant temp sensor related with this truck. So I'll start with that.
Thanks again for your help!

 

[dyeager535]

Just remember that codes do not tell you what to replace. If both 14 and 15 are CTS, probably not a bad guess, but for the future remember that a code tells you what *circuit* the ECM sees an error coming from...could be a bad wire, bad connector, etc.

If you can see my signature, the factory service manual links will be helpful, as the manuals include the troubleshooting flowcharts for each code.

Report back as to your results. As things go, the CTS is a pretty common failure, but "common" just means we see/hear of more CTS failures than say, the knock sensor. Most of the sensors are pretty darn robust. The inside of the CTS is stupid simple, the only way I can see them failing is a broken internal connection, but it must happen!

 

[Lov-2-Rev]

Awsome info...much appreciated!
However, I may have misinterpreted the code. It flashes 1 - 2 a few times then it flashes 4 - 5. Which goes back to the O2 sensor. I'm wondering if the sensor is too far down stream in the exhaust to function properly, and that's why the light only comes on after a little while of driving.

 

[Supervillainmc]

Those cooling temp sensors don't last very long. I changed 3 in 10 years. Very easy to get to and change.

 

[dyeager535]

My CTS has been on the truck for 10 years. I'm only using older OEM Delco stuff, aftermarket/new Delco/Delphi stuff is probably Chinese so all bets are off.

This is why a data tool of some sort (autoxray or tunerpro RT/ALDL cable) can be helpful. You can "see" what the sensors are doing, and if the data being reported is what it should be.

What kind of O2 sensor did you use? As with everything, these things can be bad out of the box.

Code 45 is what? Rich? Lean? The "lag" in the exhaust can cause some issues, but I ran mine WAY past where they were stock, and didn't have any issues related to the distance. I can't get the pic to display, but here is the link http://i831.photobucket.com/albums/zz231/dyeager535/Picture1022150856_1.jpg The bottom header is what I ran for 10 years, and the O2 was past the collector. All issues were related to exhaust leaks, which weren't the headers fault. If the O2 was forward of the ball/socket connection, I would probably have never had an issue.

I had a non-heated O2 on there for about 8 years, then switched to an AFS-74 (GM heated) O2. The non-heated ran open loop at idle, but instantaneously went closed loop with ANY throttle, FWIW. It wasn't a real issue, although with my poor tuning skills, it idles better closed loop than it does open loop.

 

[Lov-2-Rev]

On the 89, code 45 is a rich mix.

"Oxygen sensor voltage was over 0.7 volts for 30 seconds of closed loop operation with a throttle angle between 2% and 20%.(Rich Exhaust Indicated)"

 

[dyeager535]

Probably not an exhaust leak then, typically shows as lean. O2 is likely working since it's

I'd find and run down the troubleshooting flow chart for that code in the proper manual here: http://67-72chevytrucks.com/vboard/showthread.php?t=545416

Pretty sure the '87-91 R/V TBI setups are identical other than how VSS is handled, but VSS should have no bearing on your problem.