350 TBI Runs Rough

[jdusten]

So I have an 87 Silverado half ton. 350 TBI with turbo 350 trans. It runs awful until up to operating temp and still lacks power then. it turns over for a few seconds, then has a fluctuating idle until warm, once put in gear the idle speed lowers (no tach so not sure on rpms) and taking off from a stop it bogs out, stalls, sputters etc. Its got a new fuel and air filters, plugs, wires, cap, rotor, IAC valve, MAP sensor, throttle position sensor, injectors, and fuel pressure regulator, and some new vacuum lines (not all of them have been replaced) I've turned many a wrench in my day but am no means a mechanic and this truck has got me pulling my hair out trying to get it to run right, Its straight piped and the exhaust ends about where the fuel doors are. Any help would be greatly appreciated!

[XrayTedd]

Did you disconnect the esc before setting the timing? Check your fuel pressure and vacuum readings.

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[Irish_Alley]

http://www.73-87chevytrucks.com/techinfo/TroubleshootingTBISystems.pdf
for starters lets start with this

heres this
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0
for testing sensors. also check for vacuum leaks around the tbi base plate and the tbi itself and maybe unplug the egr vacuum to see if its stuck open

[Captain Swampy]

Could be the EGR valve. Bedazzled runs like crap when the EGR doesn't work.

[XrayTedd]

Any new updates on this?

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[VileZambonie]

Check for vacuum leaks, check the TBI base gasket, make sure the map sensor hose is connected.

[Flyinhillbilly]

You might try a coolant temp sensor. I've seen a lot of them go bad and cause the ECM to think the temp is -40 and that makes it dump the fuel to it.

[Irish_Alley]

i would have to disagree and this is just my opinion. if the cts is reading cold it will default into a open loop where the settings are preset and dont depend on a sensor signal. once to operating temp the ecm changes setting depending on senor input, if it changes from open to closed then the cts should be working correctly but only a test on it would tell you either way. since it runs crappy all the time vacuum leak is the most plausible in my mind

[Flyinhillbilly]

I've been a professional mechanic for 20 years now, and I've seen this many times. The ECM just reads what the sensor tells it, it don't know good info from bad. TBI's were really crude.

[Irish_Alley]

well i worked at autozone for almost 2 years  lol. but no doubt the cts will cause it to run rough. seen one with a broken wire, would smoke real bad and run like crap and not go into closed loop. but since he says the performance changed once hes in closed loop i would think the cts is getting the correct signal to the ecm about the coolant temp. but this is all not worth discussing if he doesnt test the sensor or check for vacuum leaks

[Flyinhillbilly]

I'm thinking the 02 sensor is reading bad rich, and causing it to pull as much fuel as possible. I'm not sure about that part, but I've seen the CTS cause exactly what he's describing. Not saying that's for sure it, but for a $15 sensor that takes 5 minutes to put in, it's worth trying.

[bd]

Perform some basic checks before throwing parts at it...

Check for vacuum leaks, check the TBI base gasket, make sure the map sensor hose is connected.

You replaced the fuel pressure regulator, but did you actually check the fuel pressure with a manual gauge? ...Needs to be within the range: 10 - 15 PSI (~12 PSI is common).