'95 350 TBI cold weather questions?

[Old Blue]

My '95 C2500 doesn't seem to like the sub-zero temperatures we're experiencing in the upper Midwest. It cranks over longer than the '99 K1500 obs I used to have. Plus for the first few minutes after I start it, it smells like raw fuel is coming out the tailpipe. I don't know if this is typical of TBI engines, or if I need to be looking into that. It only does it during this really cold weather.

 

[c1500deathtrap]

It is rather typical of wet flow manifolds.

 

[90halfton]

My 90 fires right up at any temp. Was -20 wind chills the other morning and it took a little throttle blip (as it always has when it's that cold). Smelling gassy is just how it is. Keep in mind it's basically a fancy carburetor. Mine runs and starts like a top and it hasn't been touched in 28 years, kinda scared to ever touch it lol.

 

[2 Sweet]

My '89 starts up just fine in this 0* bullshit, idles pretty high until it warms up which I assume is typical. But if I try and drive it cold, it stumbles something terrible at low RPM's, completely falls on it's face, but runs great once warmed up.

 

[JCribb]

If it smells rich, like super rich like your describing, I suggest some AC Delco ecm temp sensor (on the intake manifold) <— this controls the computer, and swap out the coolant temp sensor (in the driver cylinder head.) This one controls the temperature gauge.

I have been dealing with this particular issue on mine for over a year, and a retired GM tech listened to it and pinpointed the problem and parts, and he also said that these two sensors need to read within 10* of each other. I myself had tried three parts store sensors with no luck, so I’m going to recommend AC Delco parts. Yes they are expensive as in about $70 (total from the stealership), but I will get my receipts in a minute and get you those OEM numbers to hunt down a better price. Replacing these parts instantly stopped my raw rich fuel smell.

If you have a high idle issue at all, look at the idle air control valve (the big sensor on passenger side of the TBI unit)

 

[Blackwater]

Typically when the temps are low the computer runs rich to warm up the engine faster to operating temps. That's why the tech asked you how long have you been running the vehicle. So that the computer starts adjusting the correct Air/fuel ratio (AFR).

 

[DerekTheGreat]

Like what others said, it's really just a fancy carburetor and that smell is typical of wet manifolds. Instead of a fast idle cam & choke, you get cold temp enrichment & a high idle until it starts to see warmer temps. When its cold & RPM's are low the fuel wants to drop out of the air and condense on the intake and cylinder walls so to compensate you have to richen the mixture and increase the idle. Carbs do it with a choke and high idle cam, TBI is SMRT. Until it gets dumb input from sensors that go wonky. In order to go into closed loop the computer must see run time for at least 2.5 minutes and there is a base temperature the thing must reach. At that point you'll also notice the idle starting to come down. I don't remember what temp that is exactly with my truck but it will start to smell better and idle at 600-650 at the 3rd "notch" from the left on my temp gauge. The computers temperature sender is separate from the one in the cylinder head, the two are independent from each other so the most important one is the one for the computer, located near the thermostat housing.

 

[JCribb]

Here are the part numbers to the sensors:

ECM temp sensor: 15326386 I paid $37 dollars from the stealership, but I needed it ASAP. I recommend shopping around for a better price. I just now googled this part number, and summit racing has it for $16, GM parts center has it for $20.

Cylinder head temperature sensor for the gauge: 25037332 I paid $22 from the dealer, which is close to what you find on the web. A quick search on this one retail is between $15-$25.

I said it yesterday, but it's worth repeating, the 38 year GM tech said these two sensors should run within TEN degrees of each other. I have no clue how to measure that by hand or how it works, but I am passing on information I received. I do know that installing these two OEM sensors definitely solved my problems of running rich, sputtering, and popping.

 

[chipskittles]

Just wanted to throw this out there, the gauge sender JCribb listed, while the correct part, may not work correctly with the gauge. The gauge may read very very low with this sensor. Hopefully the supply chain has been corrected by now but as of a couple years ago the sensor, while it is indeed the "authentic GM part", did not provide the correct values for the gauge to work properly.

I am of the same opinion on sensors and changed both the ECT and the gauge sender at the same time, using genuine AC delco "Original Equipment" parts. In my case, I found that the gauge reading was very low with the new sensor, like truck fully warmed the gauge would be at 9 o'clock. After reading up on the issue I found a lot of people had the same problem and said in this case the aftermarket part worked better.

I ended up just putting the 24 year old sensor back in. I think I need to revisit this now. I hate relying on old sensors to tell me what my car is doing.

TLDR; if you change out the head sensor and the gauge reads low, it's a problem with the new design of the sensor. Get a sensor from a different supplier other than AC-Delco.

 

[Blackwater]

mine does that with the aftermarket one.