87' 305 Hard Starting

[phattailrider]

Just bought an '87 305.
It takes about 12 - 15 seconds before it fires up.
After it has started up and i shut it down,
it still takes about 5 seconds of cranking to re-start.

With a TBI does fuel squirt into the carb when i
press the gas peddle to start it up or does it need to
be running for fuel to be delivered to the intake ?

Are there any starting procedures i should follow ?

Are there other things i should test or check that could
be causing it to take so long to start ?

Thanks !

Phattailrider

[RandyP]

Have you tried turning the key to run for a few moments before cranking? I know with my 87 I just turn the key on, then start cranking after about 5 seconds. That lets the fuel get where it needs to go faster, instead of while cranking. You should not have to pump the gas with a TBI, good way to flood it.

[rfmaster]

Originally Posted by phattailrider

Just bought an '87 305.
It takes about 12 - 15 seconds before it fires up.
After it has started up and i shut it down,
it still takes about 5 seconds of cranking to re-start.

With a TBI does fuel squirt into the carb when i
press the gas peddle to start it up or does it need to
be running for fuel to be delivered to the intake ?

Are there any starting procedures i should follow ?

Are there other things i should test or check that could
be causing it to take so long to start ?

Thanks !

Phattailrider

TBI does not have a carburetor - it has a throttle body. When you first turn ignition key from off into run position (before cranking) the ECM will power up fuel pump for about 2-3 seconds as part of the system check (POST). You should be able to hear fuel pump operate. As part of self test the SES light should be solid - blink off - back to solid on. If the fuel pump does not turn on then check fuel pump relay mounted on the fire wall. 9/10 times the socket contacts get corroded preventing fuel pump relay from operating. GM put a back-up system - oil pressure operated switch which sits in parallel with relay contacts. Oil pressure switch will close its contact when it sees 6+ PSI of oil pressure. Naturally, it takes a bit of cranking to build up oil pressure and consequently for oil switch to close its contacts powering up fuel pump.

Do this basic check and post what you see.

//RF

[Goldfinger]

Thats odd even with a carb mine will take 5 sec cold and about 1 sec hot. Just got to pump it. but turn it to run for 5 sec then attempt to start it. Have you considered a tune up? New plugs/wires/cap/rotor/filters/coil- it always helps

[turbo350]

If it turns out its not fuel related could be an array of things. I had a hard start issue on my tbi 350 which turned into a no start situation and turns out my ignition module went bad. I replaced that as well as plug wires and dist cap as long as I was at it, problem cured.

[wheels67]

Since its only hard on start ups. I would think the O2 sensor is dying. Do a resistance test with an ohmeter as per the repair manual. But like someone said it could be a few things.....

[Mattsch18]

im having a simiiar problem on mt 76 but mins carbed witha eblbrock elec. choke carb, dosent seem to manna start alot of times right away, any ideas?

[rfmaster]

Originally Posted by wheels67

Since its only hard on start ups. I would think the O2 sensor is dying. Do a resistance test with an ohmeter as per the repair manual. But like someone said it could be a few things.....

O2 sensor input is not used by ECM during engine start. During start ECM operates from stored fueling tables while making injector pulse width adjustments based on engine coolant temperature and other parameters.

Checking O2 sensor with ohmmeter will yield absolutely nothing. O2 sensor can be thought as a voltage generator - a “Galvanic Cell”, a type of battery. The O2 sensor contains two porous platinum electrodes with a ceramic electrolyte (Zirconium Dioxide) between them. The Oxygen Sensor generates a very small voltage, ranging from as little as 100mV (0.1 volts), up to a
maximum of 900mV (0.9 volts) dependent upon exhaust gas oxygen
level.

Spray a little bit of gas or WD40 into TB during cranking - if it immediately fires you have fuel delivery issue.

//RF

[wheels67]

Originally Posted by rfmaster

O2 sensor input is not used by ECM during engine start. During start ECM operates from stored fueling tables while making injector pulse width adjustments based on engine coolant temperature and other parameters.

Checking O2 sensor with ohmmeter will yield absolutely nothing. O2 sensor can be thought as a voltage generator - a “Galvanic Cell”, a type of battery. The O2 sensor contains two porous platinum electrodes with a ceramic electrolyte (Zirconium Dioxide) between them. The Oxygen Sensor generates a very small voltage, ranging from as little as 100mV (0.1 volts), up to a
maximum of 900mV (0.9 volts) dependent upon exhaust gas oxygen
level.

Spray a little bit of gas or WD40 into TB during cranking - if it immediately fires you have fuel delivery issue.

//RF

Hmmm. Wouldnt the tables be affected by the last reading of O2 while running at idle? Stored in ecm by previous run? Say its running rich when shutoff and adjusts fuel/air or timing table?? Interesting stuff.....So how do you test an O2 sensor?

To the starter of the thread....Do you smell excessive fuel out of pipe when strarting or do you have to open the throttle a little for more air????

[85Bowtie]

I would check where your ignition timing is set before i start replacing stuff in your distributer. A little too advanced will do what you're describing.

[rfmaster]

Originally Posted by wheels67

Hmmm. Wouldnt the tables be affected by the last reading of O2 while running at idle? Stored in ecm by previous run? Say its running rich when shutoff and adjusts fuel/air or timing table?? Interesting stuff.....So how do you test an O2 sensor?

To the starter of the thread....Do you smell excessive fuel out of pipe when strarting or do you have to open the throttle a little for more air????

During start ECM uses stored fueling data (actually VE values) to calculate injector pulse width. O2 sensor input is not used during start because it must be heated to about 600F before it can generate voltage. It takes time for O2 to be heated to 600F - this is why later generation PCMs use heated O2 sensor to bring it up to operating temperature quickly. Even though, heated O2 sensor still requires warm up time, but it is a lot faster than a single wire sensors found in OBD-1 trucks (87). For the first 2 minutes, depending on coolant temperature, ECM will operate in open loop (OL) by deliberately supplying rich fuel mixture (about 13 to 13.8:1). This allows engine and O2 sensor to warm-up quickly. Also, depending on calibration, AIR pump will dump air into exhaust forcing CAT to heat up to normal operating temperature. Once coolant reaches 45C (calibration dependent) or more ECM switches to close loop (CL) operation by shutting AIR divert valve and monitoring O2 voltage to compensate fuel mixture. Once in CL ECM will use previously learned BLM values to compensate fuel mixture better (and faster).

//RF