305 SBC TBI hard winter starting (1990)

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Recently brought my 1990 Chevy Caprice back from the dead (from a known failed fuel pump really) back in december, had to pay professionals to do it cuz everything else was broke, at the same time if I remember right (trying to keep straight what was done on each vehicle) i'm pretty sure they also changed the distributor cap, plugs, and wires as part of a getting it back to running state. I love driving it again minus the poor MPG (compared to my saturn which needs a clutch/too cold to do til summer) but it's not a happy winter starter.

1990 Chevy Caprice, 305 small block chevy v8, ~160,000 miles, which doesn't want to ever start below 0, and just gave me the hardest starting experience at +12. It just acts like it's "nearly" catching but never quite gets there, I commonly smell fuel almost like its flooded but a TBI shouldn't be, and the only way I got it to light after 120 seconds total of cranking was violently mashing the footfeed which again I should never have to do while cranking it.

This confuses me because my pickup is nearly identical, which is a 350 small block TBI has been starting to -10 without a complaint really. (haven't tried that one below there yet)

If I can plug the block heater in it starts easy the problem is sometimes I have to park where there isn't one. I already learned the hard way it wouldn't start at exactly 0 (3 degrees is a horrific struggle just barely catching) or anything below and don't even try anymore. But it was predicted to be 12 so I thought it'd be safe to park it on the street yesterday. Exactly what happened is monday-into-tuesday night it dipped to -10 below. It was back to 5 degrees by noon, I try to start, no start. I smack forehead with palm realizing the cold probably soaked the engine block and this white car covered in snow isn't going to get much solar gain. But 12 hours later the rising temperature is 12 degrees in the middle of night AND IT STILL WOULDNT START at midnight. 18 hours later, right now literally just this second still at 12F outside it just BARELY started after 120 seconds of cranking.

I'm not sure if thats just how long it would take the air to raise the subzero temperature of the block to above freezing, or if it's actually getting WORSE which is a bad sign because i'm totally tapped out having spent too much on car repairs. Since the distributor/plugs/wires i'm 90% sure were replaced that leaves me things like a computer, the OBD-1 system isnt throwing any codes about obvious sensors out, the fuel pump and filter is new and it's been running the last 6000 miles happily to school and medical out of town since Dec (I have to drive alot) so it's not something that's been obviously different... i'm just alarmed cuz either large blocks of iron really do take 18 hours to rise from -10F to +1F (for how hard it started) in +8 to +12 degree air or something else in the car is degrading and I better start to have an idea of what before I get stranded. >_
PS: Just to be clear, I warmed it up 20 minutes, then turned off and on to restart - restarted in under a second with no problem like usual. So this is more grasping to figure out one of three things, 1) is that just how long it takes for an engine block to warm that much if it was supercold, 2) are TBI SBC's in general hard winter starters below freezing, and 3) what I might watch out for possibly degrading in the future. (like I had the engine computer crap out of my pickup and I now wonder if I should be preemptively playing parts cannon to replace it in the caprice during summer due to being 30 years old or if that's silly :p )
 
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My 89 that I had before my current carbed 83 had 332k miles at the end and would start right up at -32 celsius just the same as if it was +32. Only time it ever threw a code was when the map sensor vacuum hose broke off.

Maybe a coolant temp sensor is bad? Going to need some diagnosis. There are not a lot of parts to test but I think that would be one of the first ones.
 
Answer to number 2 - my experience is that TBI 305s start perfectly in the cold when they are working right, even with a ton of miles and no new parts. I never used the block heater on mine.

It annoyed me that they would crank long on a normal temperature cold start (like 1.5 seconds maybe) but on the coldest days they didn't take any longer than that. My carbed one starts instantly on a warm day but on the cold days it cranks maybe 2-3 seconds if it's -20 or folder out.
 
Since it starts fine warm, I assume that fuel delivery and spark are normal. So, the issue is likely insufficient fuel when it's cold. I would start with the temp sensor as well.

In older fuel injection (like the Bosch K-jetronic I had on a few cars), the "choke" is a function of temp sensor reading. Cold engines require extra fuel.

If the FI doesn't know the actual temperature of the engine, then, the colder the engine becomes, the greater the discrepancy between fuel required and fuel delivered.

There may be a separate temp sensor for the FI, so while your dash gauge works OK, you need the FI temp sensor.
 
Have you ever "rebuilt" the TBI? It's an easy job.

What about checking the timing? You'll need a timing light and need to unplug the timing wire from the firewall cluster. It's easy peazy.
 
Originally Posted by columnshift
right now literally just this second still at 12F outside it just BARELY started after 120 seconds of cranking. ..... I now wonder if I should be preemptively playing parts cannon to replace it in the caprice during summer due to being 30 years old or if that's silly :p )


Bad fuel pressure regulator. Sitting for so long made it stiff.

Originally Posted by Phishin
Have you ever "rebuilt" the TBI? It's an easy job.... It's easy peazy.


Bingo. That should fix you right up.
 
I don't think so. Either of those items would cause issues hot or cold. I'm still leaning towards the most likely problem - coolant temp sensor maybe even air intake temp sensor.
 
Btw I swapped the 300k+ mile throttle body on my car for the 220k one from my parts car (in attempt to gain fuel mileage because it wasn't getting as good mpg as my previous carbureted ones). It ran the exact same before and after the swap. I've heard of fuel pressure regulators failing on these. They will run terrible all the time from what I've heard. When the throttle body wears out the throttle shaft bushings wear causing a vacuum leak which will cause it to run terrible (again - all the time). Which is why the don't think these have anything to do with your issue.
 
Similar problem with the 95 GMC diagnosed it by jumping the alldata port under the dash. Replaced the air intake sensor with one from a junker S-15 GMC four banger. Believe Auto Zone can help with diagnostics. Would not change anything with the shotgun approach
 
Except in his case he has no codes, these cars don't set a code until a part is completely failed or way out of parameters. I would still bet on a temp sensor but they need to be tested with whatever procedure is in the service manual. There's no reason to have to replace both when it's likely only one is bad or it's something else completely.

An o2 sensor won't affect anything until the car is warmed up and in closed loop so hopefully nobody here suggests that. I'm not sure about the map sensor however. They can fail (but mine was still original at 332k miles). I'm not sure about my other sensors, they may have been replaced by the original owner (I was the third).
 
Check your coolant temp sensor with a multi meter. I don't have my sheet handy but there is many on the internet. There is an approx. resistance for a given temperature. Check its cold reading and once it is at operating temp. This should give you an idea if the sensor is bad.

How are the plugs, wires, cap and rotor? Timing?
 
coolant temp sensor and the ground cluster near the water outlet.
top 2 causes and both are cheap and easy.
the fpr normally causes problems at high rpm/load.
and its usually a rotten spring from a clogged pcv system in the tbi base.
 
We have a 1991 Caprice 5.0l . After setting over night , it has to crank for several seconds , before it starts . Fuel pump has been replaced . TB pressure regulator has been replaced . External fuel filter has been replaced

After once being started , it starts fairly quickly / normally , the rest of the day .

When cold , the exhaust smells rich . This goes away after it warms up .

No easy way to check fuel pressure , at the TB .

This car belonged to Mom and Dad before they passed away . Has been parked mostly since . About 46,000 actual miles , so , nothing is worn out , just old and set for a long time , with brief periods of being driven .

I wonder if there is a way to check fuel pressure , taking loose the fuel filter and using a tire valve , clamp & short length of fuel hose ?
 
Here is the resistance chart for the CTS.

GM Coolant Temp Sensor.jpg
 
Originally Posted by BrianF
Although does the engine even use the MAP and CTS for cold starts?


CTS yes. Map sensor I think so. I believe my car was cold when I started it up and it was missing and flashing the check engine light (map sensor hose had broken off). But that was close to 10 years ago so I could be remembering wrong about the map sensor.

The CTS is the main source of info for it to set the mixture on a cold start AFAIK.
 
The MAP sensor vital for the primary air/fuel control on that system. They do not have a MAF sensor.
 
I believe the CTS is probably more likely to cause the cold start issues as the map sensor would probably cause it to run terrible hot or cold, but no guarantees on that. Coolant temp sensors I have seen cause trouble only during cold start or only after getting up to a certain temperature.
 
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