LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
😭😭😭 I am not gonna lie I am a shade tree mechanic at best. As well as I'm kinda a techie so I'm in love with my obd2 setup with live diag. Grant it I'm not always sure at what the values mean then spend days on youtube gathering data lol. But now I have hit a road block youtube has very limited info on the 1992 buick century custom 3.3L. I was given this little wagon and let me tell you it was pretty rough. but it had like 60k original miles and the interior brought me back to a place of nostalgia when I first started driving. So I decided to fix it up a bit and make it my daily driver, with future plans of basic restoration. Kind of a project car to learn some of the jobs I've never attempted...With all that said all good things come to an end and usually leave you stranded on the side of the road. I've been learning how to diagnose ob1 technology (paperclip) and wow this is way tougher than obd2 diagnosis. I got four codes total. Off the top of my head I remember code 22,23 and their were two more in the 30's but I forget at the moment. But the jist I got from it was a problem with multiple fuel air ratio components. I got it to start and idle again, it idles fine but once I put it in gear it Boggs and occasionally backfires. When it gains a bit of speed It starts lurching. I dont have a tach In this model so I cant tell what the rpm is actually doing. There is also a strong order of gas from the exhaust along with a tiny amount of white smoke occasionally. The weird thing is it seems to get worse as engine warms up. So this is what I've done so far.. Replace vac lines from TB to charcoal canister, as well as from FPR toTB, replaced FPR, as well as fuel filter. tested injectors with screwdriver all were spraying. backprobed tps voltage was low I adjusted it back to spec(.38 at idle). tested following connectors map,iac,purge solenoid all were getting 12v from ecm and tps was getting 5v constant. At this point I'm guessing, and I'm definitely not rich enough to continue blindly throwing parts at this thing. any help to diagnose this old wagon would be greatly appreciated.
 

CorvairGeek

3.8L Member
404
101
43
The Gem State
Buick Ownership
1996, 92 Buick Century
Check the resistance of the temperature sender for the ECM. If the computer thinks the engine is cold, you would get these symptoms. Let us know what the codes are. If one of them is for temperature sense open, if would definitely give these symptoms.
The 3300 is an excellent engine. I love ours better than the 3100 we bought new. They just don't quite have the proper idle qualities due to being a 90 degree V6 without a counter balance shaft like the 3800 (though they were cast and partially machined for one).
 

chem_man

Buick Newbie
99
24
8
Fallston, MD
Buick Ownership
1999 Century
OBD I Code 22 translates to an throttle position sensor error - low output, and OBD I Code 23 translates to an Intake Air Temperature (IAT) Sensor error - low temperature indicated.

I would check to see how smoothly your throttle position sensor (TPS) changes resistance by back probing it with a DMM and watching the resistance scale. If it changes abruptly, I would change the TPS. Also check for broken or loose wires going to the TPS connector.

I would go ahead and replace the IAT sensor if you cannot find a broken or loose wire going to it.

Either one or both of these errors can cause the engine to run rich.
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
I ran the codes today it's kind of a laundry list as follows.

12,22,26,27,28,34,39,45
______________________________
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
Well this may not fix everything but I've definitely found a problem key on engine off fuel pressure 18 to 30 PSI from what I'm understanding it should be in the mid-forties it has a brand new fuel filter an fuel pressure regulator so I'm assuming it's time to change the pump also snap throttle is dropping to 20 psi from around 30
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
Okay so now I'm not so sure I bought a Haynes manual and it's telling me my fuel pressure should be 30 to 44 PSI while I am on the low end of that Spectrum I am within specifications I'm definitely burning rich and the engine is having trouble idling rather it feels like it's missing at idle what should I replace I'm thinking throttle position sensor first since it's definitely out of spec
 

chem_man

Buick Newbie
99
24
8
Fallston, MD
Buick Ownership
1999 Century
I see why you want to change out the TPS, but because you are getting a CODE 26, that indicates there is a problem with a Quad Driver Module which is part of the engine control module (ECM). Since you are getting a CODE 12, that indicates that the ECM is likely good, but the #1 Quad Driver Module is shutting down to protect the ECM from getting fried. Something on the #1 circuit is shorting out or going wonky and causing QDM 1 to shut down.

I found this discussion of the Quad Driver Module(s) and ECM and it would be well worth your time to read it, refer to your Haynes manual and do some digging. Now, just because the author of the thread had a bad crankshaft position sensor does not mean that is your problem.


Good Luck!
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
Out of curiosity since a lot of these sensors and module share the same ground could this not be a code stacking effect caused by say the TPS voltage being out of specification... just a curiosity because they mechanic friend of mine told me that the qtm module controls the sensors and if one is bad since they share the same ground it can give false Cel and do something called code stacking so basically 1 sensor is bad and the rest of them give false check engine lights that's the idea what do you think possible?
______________________________
 

chem_man

Buick Newbie
99
24
8
Fallston, MD
Buick Ownership
1999 Century
Yes, that is a possibility. Anything on that circuit could pull down the sensors on that circuit.

The question to be answered is "Why is the TPS voltage out of spec?"

That's why you need to look over all the wiring you can see to make sure that the insulation hasn't melted in one spot and the wire is touching the engine block, an exhaust manifold, the EGR tube, etc. Also look for plain broken insulation that is rubbing against something metal. Investigate first, find out what is wrong, what is right and diagnose. Just don't go on a buying spree purchasing parts.
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
Well in my defense I think I'm improving LOL. I used to would have looked at a code then bought the corresponding part at least I backprobe the sensor LOL
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
I'm just really unsure in where to even start with tracing the wiring. I've never really done that kind of diagnosis in my life it's a little bit daunting any tips or complete job walk through instructions LMAO
______________________________
 

chem_man

Buick Newbie
99
24
8
Fallston, MD
Buick Ownership
1999 Century
Make sure you have a Digital Multi-Meter (DMM), a set of clip leads and some sewing pins or needles.

Look at the schematics in the Haynes Manual likely engine controls. Locate the various components like the IAC, TPS, ECT, etc. on the schematics and note the wire colors. Now follow the lines on the schematic from the component (such as the TPS) to the block that represents the Powertrain Control Module (PCM)/Engine Control Module (ECM) and verify the wire colors and the pin number for the connector.

OK, now you will want to disconnect the connector at the PCM/ECM, find the pin number, make sure the color for the TPS corresponds to the correct pin number, and insert a pin or needle into the appropriate wire from the rear side of the connector. Now go to the TPS and with the connector still attached, back probe the appropriate wire and connect the pins to the DMM leads using the clip leads. Make sure your DMM is set to the low Ohms range.

You might also want to check that the wires have not grounded out by removing one of the back probe pins, and touch that lead to the body/frame/engine bolt to see if it is grounding out between the two points on the circuit.

Follow what I am saying?

Now move onto the next wire. After 5 or so of these tests, you'll get the hang of it.
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
The only thing where you lost me was at the end with the process of checking if its grounded out
 

CorvairGeek

3.8L Member
404
101
43
The Gem State
Buick Ownership
1996, 92 Buick Century
Besides anything suggested, take a quick look at the engine grounding and make sure everything is intact. This picture shows where all the grounds connect to the timing cover. You can see the oil filter in the pic to orient yourself (passengers side wheel well). This is from my '92 3300. Even labeled some items. Buick Detailed.jpg
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
So I'm gonna unplug PCM find tps wire stick a needle through the insulation intowire connect alligator clip to needle connect alligator clip to dmm(positive or negative?) Then back probe same wire with tps connected measure with dmm on low ohm setting (what kind of values sm I looking for?) Also do I test all wires in this manner....also does 5v constant and signal wire both connect to pcm... as you can tell I've never done this before
______________________________
 

chem_man

Buick Newbie
99
24
8
Fallston, MD
Buick Ownership
1999 Century
OK, the first thing you should do is to open your Haynes Manual to chapter 6 (Emissions and Engine Control Systems) and read it before you proceed. It will be invaluable to you. It provides all kinds of information, such as what resistances to look for, what voltages, etc., and I believe it's all on Page 1. Also, Chapter 5 will be of assistance.

By grounding out I mean to check the wire relative to ground to see if the resistance between the wire and ground is zero ohms (or close to it). Most wires will not read zero ohms if you attach one lead of the DMM to the wire and the other lead to vehicle ground. NOTE: Some wires will read zero ohms when you do this because those are ground wires. For example, if you measure the resistance between vehicle ground and the negative battery terminal you should read 0 ohms. However, if you measure the resistance between vehicle ground and the positive battery terminal, you should see at least several hundred or thousand ohms or more, and if you see zero ohms, you are in real trouble!

By checking to see if something is grounded out, you are looking for a short, as in a wire that is laying on a piece of metal and that wire's insulation is nonexistent in that spot.
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
Ok thanks... I'm familiar with the terminology just using the dmm fpr troubleshooting a ground is new ground for me....I also think I understood the procedure...I'm just a visual learner so painting a picture in my head based upon written instructions is often challenging for me but I think I get it now will be doing some work on her today will let you know my progress
 

LucianTitus87

New member
18
1
3
Buick Ownership
1992 Buick Century Custom 3.3l
I had already ordered a throttle position sensor and I got it in today so I went ahead and put it on and about 90% of the problem is fixed it's running great now but I'm not sure the idle if perfect I'm going to pull the fuse for the ECM to reset the codes and recheck them unless you have a better way of resetting the ECM without a OBD1 scan tool


Also when testing the voltage on the old throttle position sensor the rise and fall was so sporadic I honestly suspected a bad sensor from the start but it wasn't sure until I hooked up the new one the voltage read so much more smoothly with the new sensor
 
Get your turbo buick badge right here!
Top