Hey everyone,

I could really use some help. I just inherited a 1987 K5 with the 350 TBI. I’ve got a lot of questions and quite a few issues with it that need to be fixed. So I’ll start small...

First things first. I got a hold of an OBD1 scanner. Here are my codes: 31, 32, 33, 34, 43, 52, 54, and 55.

The research I’ve done is telling me Park/Neutral Switch, MAP, EGR, EST/ESC, Oil Temp Sensor, Fuel Pump Circuit/Relay, Then ECM/PROM.

Any thoughts or advice?

The park/neutral switch is a no brainer. But with all the other ones, each of the codes for non-ECM/PROM codes (i.e. MAP, EGR, etc.) also say the ECM/PROM. There is no dedicated ECM/PROM codes.

So, I’m wondering if all the non-ECM stuff is actually what’s wrong and the ECM codes are just tag alongs? Or is the ECM screwed and that’s why it’s throwing all the other errors? I’m not made out of money. How do you vets recommend I tackle this?

After I get this figured out I’m gonna start posting a bunch of pictures or random loose wires I’ve found asking for some help identifying those.

any help you all can give me is greatly appreciated!

Very Respectfully,
Evan

 

Welcome!

Here is the Factory Emissions Manual listing of the codes:

Code 31 isn't present in the listing for some reason, but I believe it to be another MAP related code, not a Park/Neutral code which wouldn't likely be monitored on these trucks.

I would start by trying to make sure that everything is wired up correctly and that nothing is shorting out. With all of those codes for the MAP sensor, it would lead me to believe that there is a problem with the sensor or circuit that is causing random open/shorts. While you're verifying the wiring, you may find the cause of the other codes.

I am going to try to get you some information that will help you in identifying those wires as well. Working on 40 year old vehicles can be interesting! You never can quite tell what's factory and what's backyard enginerding.

*EDIT*
I did some reading up on the CALPAK & Faulty ECM codes and here is some info I found on a Fiero forum:

 

Swartlkk,

I really appreciate the info. Huge help, and massive time saver!
I went digging into the engine bay and found there is no EGR pump, and the AIR canister thing is gone as well. Additionally, the truck has been given straight through dual exhaust. Only the downstream O2 sensor is installed with cats, while the harness for the upstream is just hanging out and empty.

I’m thinking about welding a bung in for the upstream and throwing in a sensor. But as far as the EGR, how can I delete it fully? And what changes would I need to make to the ECM? I’ve done a lot of digging all over the web and in several forums and threads, but haven’t found any two answers the same.

Lastly, got a few pictures here. Random wires hanging out that I have no clue what they are. I haven’t even begun to tear into the inside. Got like 10 wires just hanging down from behind the dash. I’ll likely have pics of those in about a week.

Any help or guidance is greatly appreciated.

Thanks!

On passenger side 1/2

On passenger side 2/2

On fire wall 1/2

On fire wall 2/2

Hanging off of distributer

Running through fire wall on drive side 1/2

Running through fire wall 2/2

Hanging near side of transmission on passenger side 1/1

 

I have a '90 'burb in the barn that I'm going to try to get some pictures of for you that hopefully will show some of these areas. It is bone stock as I bought it from a local community college that used it as a maintenance vehicle for 30 years just driving their private roads. Much of it should be almost identical to what you're working with. It's currently 12F out this morning though so it might not be until later today when/if it warms up.

I think the single wire that you see near the distributor/coil is the tach probe connection for probing/testing the tach signal output of engine RPM.

I have done a little reading on the whole dual exhaust & O2 sensor conundrum and found that most just say to install it in the passenger side exhaust pipe fairly close to the header even though this will only be reading one bank of cylinders. I would just get yourself a weld in O2 sensor bung and install it in the side of the exhaust pipe behind the collector on the header. The upstream sensor is necessary for the ECM to properly fuel the engine. The downstream sensor is only a catalyst efficiency monitor and has no bearing on fuel delivery.

One thing that I know is a problem with the early 1 wire setups like your '87 has when coupled with an aftermarket system is sensor efficiency as O2 sensors need heat to operate properly. The stock exhaust systems run quite warm, but a performance oriented system may not keep them properly up to temperature. As such, many recommend upgrading to a later 3-wire sensor. The Caspers Electronics HO2S Retrofit Kit 103025 from Summit Racing includes pretty much everything to upgrade your upstream sensor.

Many of those rubber lines in the engine compartment on the driver side would have been part of the evaporative emissions system that looks like is no longer there. There would have been a EVAP canister located behind the radiator core support down low.

On the rubber hose at the trans, you'll need to trace out where it runs. It is possible it is just a vent for either the transmission or transfer case and is where it is supposed to be.

*EDIT* - Here are a few pictures I took of the '90 Suburban I have up in the barn:

EVAP Canister


Side of the TBI has the TPS (flat 3-wire) and IAC (square 4-wire). Lower and to the right a bit is the ESC and the EGR solenoid on the metal bracket.

I'm not sure what that square 4-wire plug is up on the firewall in your truck. My '90 'burb doesn't have it. I also do not know what the connector is that you have over on the driver side inner fender area.

 

I would try to get a hold onto the factory mauals, especially the electrical & wiring diagrams.

Rockauto usually has them on the literature tab for the older trucks.

 

I sent him some info through PM on that. :-)

 

Thanks

Nice that they do publish these manuals at all and at a reasonable price on CD-ROM.

 

Hey everyone,

I just wanted to thank you all for your help! I’ve gotten the engine bay mostly sorted out now and straightened up the vacuum and the PCV systems. I also got some work done on the TH400.

Right now, I’m trying to get after the bird’s nest of a wiring harness that’s behind the dash. Something in the fuse box keeps blowing fuses every time I connect the battery. I have another post about that. If you all have the time to take a look at it, any help would be amazing. I’ll put a hyperlink in below...thanks again everyone! My dad would be thrilled at how well the truck is coming along.


https://blazerforum.com/forum/lighti...x-pics-101003/

 

So update on a couple of those pictures...

Picture 1 and 2 appear to be the connection for an intake air temp switch. But I haven’t been able to find whether or not the 87 350TBI had one or not. The engine bay wiring diagram doesn’t mention it, and I can’t seem to find one that says it’s for my truck. But the ECM wiring diagrams I’ve found show a line for it. Any advice you all have would be great.

Pics 3 and 4 are for a torque converter connection for the 700R4 the truck came with originally. But since my old man swapped it out for a TH400, it isn’t in use. I’ll have to find a way to make the ECM ignore that.

Still not sure about picture 5 though. If it is a tach line, does that need to be connected to the ECM somewhere? Or is it a line that would plug directly into a tach if I had one?

Pictures 6 and 7 are a vacuum hose and a harness for a cruise control module that aren’t there anymore. I did find the charcoal canister. It was relocated closer to where the headlights are. I still need to check those lines for any vacuum leaks and stuff. But for the cruise control thing, I just capped off the vacuum hose and zip tied everything out of the way.

Picture 8 was a vacuum hose that was just dangling. It wasn’t connected to the transmission vacuum modulator, that has its own line running to the intake manifold just below the Throttle Body. It wasn’t connected to the “puke” tube on top of the transmission. I couldn’t find any reasonable place it was hooked too, and the vacuum diagrams you all hooked me up with did not mention this line either. So who knows? I ended up just yanking it out and pulling out the “Y” connector and putting in a straight connector.

I’ve still got a vacuum leak somewhere though. I’ve replaced the lines and connections. Next I need to check the transmission vacuum modulator, the charcoal canister and EVAP, and the vacuum reservoir.

I’ll update you all with everything I learn. Thanks again for all your help!

 

The tach connector is for diagnostic purposes mainly. I do not believe that it has a purpose.

I do not believe that your truck came equipped with an IAT sensor/switch.