Cold Start, Please Help!

[Sachmo]

I have a 1983 Celebrity 2.5l TBI. It virtually doesn't start cold, the warmer the engine is the easier it is to start, and etc.. I've replaced the plugs, plug wires, pcv valve, distributor cap and rotor, checked for spark, checked the fuel injector, replaced coolant sensor and tested tps(both were trouble codes)(tps was fine), fuel filter, cleaned the throttle body thoroughly(included idle speed motor). I've exhausted every possibility my feeble mind could come up with. This really sucks and I'm stumped. Any advice would be greatly appreciated. Thanks.

Jonathan

[ra11585643]

How about the choke?

[Sachmo]

Well it's my understanding that, being fuel injected, it doesn't have a choke. I wasn't very clear on that. Think it might be the fuel pump? It seems to inject fine when I take the breather off and watch it, but who knows?

[RABarrett]

Fuel injected engines do not require chokes as the computer controls fuel delivery based on engine parameters such as throttle position, airflow, coolant temperature etc. My suspicion is the fuel pump's condition. As it dies, less and less fuel is delivered to the TB unit, and the ECM cannot compensate for the dying pump. It has no way to know the pump is dying. When the engine is warm, the O2 sensor shows a lean mixture, allowing for enrichment. When the engine is cold or being started, the O2 is ignored by the ECM, due to its temperature. Ray

[ra11585643]

TBI is not regular fuel injection. Its not much more than a Carb without a float bowl. Injection takes place of the bowl, check the CHOKE !!!!

[ra11585643]

When you look into your throttle body you should see a butterfly valve, this is your choke plate. It should be open when engine is warm and closed when engone is cold.

[GMMerlin]

Like Mr. Barrett stated in his post, the GM TBI injection system is controlled by the ECM, using inouts from the coolant, throttle position and Map sensors to calculate fuel delivery.
I would check the fuel pressure...should be between 9-14 PSI with the key on..I like to see about 12-13....any lower than 9...7-8 psi will allow the engine to run, but will cause difficulty starting cold and stalling on acceleration.

ra11585643 stated:
When you look into your throttle body you should see a butterfly valve, this is your choke plate. It should be open when engine is warm and closed when engone is cold.
TBI is not regular fuel injection. Its not much more than a Carb without a float bowl. Injection takes place of the bowl, check the CHOKE !!!!

Both these statements are false! The Gm TBI unit has an injector above the throttle plate and the air is mixed with the fuel as it passes the throttle plate...there is no choke plate or any other choke type device on this setup.

[Sachmo]

Thanks everyone, I dumped a small quantity of gas down the tbi's throat and she fired right, so I'm almost positive it's the fuel pump. Even though I have to drop the gas tank to get at it, it's a relief. I'll update when I put in the new pump.

[RABarrett]

This is jumping to conclusions. As GMMerlin stated, CHECK the fuel pressure first. There are several control systems involved in fuel delivery. Though the pump is involved, there are several control systems involved in its operation. That does not include the signals necessary to operate the injectors. Without testing, you are shooting in the dark. Age and time take their toll on ALL systems involved, not just the pump. Ray

[Sachmo]

fine, I'll do it your way, I'll check the pressure first. Nonetheless, thanks.

[GMMerlin]

Don't get pissy about it...spending a little time doing some diagnosis will save you money and time in the long run