Short bio - TPI406 in a '79 K5 Blazer, original fuel tank - Bosch fuel pump in the frame rail back by tank w/IROC filter - been in the truck a year, ran fabulous till 3 months ago - no changes.

Symptom - lousy cold running. Worse today then ever, morning was about 32 degrees, coldest day so far. Then gets better when into closed loop and warmed up. NO CODES ever. At times it can be running along great, you slow down or come to a red light, go to take off, it seems it has a 4 cylinder motor in there. Pushing harder on the loud pedal gets it going, and seems to 'clear out'.

My engine builder/TPI guru (he really is a guru) has not looked at it yet. We did replace the EGR valve with no improvement. He thinks it is possibly the sock on the fuel pickup in the tank (gumming/clogging up) OR coil/ignition related.

It comes and goes. Can be running perfect and then go hooters up.

Short of getting a scanner (which I am doing) what do you guys think?

He also says it will absolutely throw a code if it is any of the sensors (O2, MAP, CTS)........is this 100% correct?



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'79K5 Blazer with 406TPI

 

Wrong about the code question at the bottom. It will not always throw a code.

As soon as the car warms up does it run fine? Is it just when the truck is sittin warming up? Without being there and the symptoms you listed, I'd say it's the 02 sensor, especially sense you said that you hadn't done anything.

I cleaned my intake out with 02 sensor safe TB cleaner and I still blew my 02 sensor somehow. It runs like crap until it warms up. It runs like a carbed car. It idles really low (400rpm) until it warms up a little bit and then it idles at around 800rpm. If I take off while it's still cold, it'll run like crap and load up on me.

If I had to take a guess though, I'd say it's your 02 sensor.

 

Blazin,

First, the failure of a sensor does not always set a DTC. A sensor that is reporting incorrect information but is still within the range of accepttable signals WILL NOT set a DTC. So even if the CTS is reporting 20°F coolant when teh engine is boiling over, the DTC will not set and the fans will not run, aside from it running poorly. The same happens with the oxygen sensor, MAT, MAP, TPS, etc. Unless the signal is at absolute maximum or shorted to ground, the ECM accepts the input.

And forget about the oxygen sensor for now. The ECM ignores that until the engine is in closed loop mode. That doesn't happen on cold starts for at least a minute of two.

Check your fuel pressure. Also, is it a MAF or MAP (speed-density) scheme?




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Later,
Vader
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If you want to beat the World, it might reach up and pull you down...
Adobe Acrobat Reader

 

running a MAT sensor (under plenum)?
youll need a scanner... drivability cant
be fixed correctly with guesses.
check fuel pump voltage, voltage drop.
what is the max flow of the pump? fuel pressure?
scan tool will show a rich/lean condition
via O2 and BLM/INT. ECT sensor could be showing
a real cold reading trying to flood -40...
O2 is distant because it sound like its going into
closed loop... if O2 is fubar.. no closed loop.
as you see it can run **crappy** without codes.
codes are hard faults the computer flags as
problems it couldnt solve with a malfunctioning
device.
airdeano