No start on crank unless I put my foot in the gas?

[blackbombshell95]

What would cause this? This is on the 95 grand prix with a 3400 swap. Heavily modified.

[2.8/3400 1985 Camaro]

Does it run ok once it does start? And I would start with cleaning up the throttle body, especially in the the throttle bore where the plate sits, and around the IAC.

[blackbombshell95]

Nothing to clean. Everything is brand new besides a few used sensors. Idles fine sort of.needs tune. Tce tb

[blackbombshell95]

Tce tb

[Blacktree]

Typically, the ECM will ignore throttle input during start-up. So I doubt it's a fueling issue. However, stepping on the gas pedal will let in more air. So chances are the engine isn't getting enough air during start-up.

Does your throttle body have an adjustable throttle stop? if so, open the throttle a little bit, and see if it helps.

[TGP37]

It does seem like an air feed issue.

I would suspect the IAC. It resets at shut down, opens all the way then closes and backs up to the determined setting for start up. So the IAC should be at the position needed during cranking.

What size injectors do you have? Maybe the needed fuel for cranking is too low for the injector to handle, min IPW. Ends up providing far too much fuel and combustion fails until more air is introduced.

Maybe your throttle blade closes 100% and the IAC can not compensate enough and opens 100% and still not provide enough air.


Strange issue for sure.

[bob442]

plugged cat.... or IAC, if this is right after you installed the TB you might have to take it for a spin to re-learn the idle, but maybe i'm thinking dodge...

[2.8/3400 1985 Camaro]

You would have to reset the ECU to relearn idle, but idk how to do that on an OBD II, on my camaro you just disconnect the battery for a few minutes and plug it back in.

[blackbombshell95]

2.8/3400 1985 Camaro, I unplug the battery whenever i'm not working on it.

Bob442, the cat isn't clogged. I had this issue with an open downpipe. And now with the exhaust hooked i'm having the same issue.

TGP37, i also suspect a faulty IAC. I can't recall if IAC's are the same for a 95 and 98. The car is a 95 with a swap harness and 98 pcm. I am positive the IAC is used and old. I have custom programming with 33# L67 injectors. I have yet to test IAC.

[TGP37]

2.8/3400 1985 Camaro, I unplug the battery whenever i'm not working on it.

Bob442, the cat isn't clogged. I had this issue with an open downpipe. And now with the exhaust hooked i'm having the same issue.

TGP37, i also suspect a faulty IAC. I can't recall if IAC's are the same for a 95 and 98. The car is a 95 with a swap harness and 98 pcm. I am positive the IAC is used and old. I have custom programming with 33# L67 injectors. I have yet to test IAC.

I know IAC's can have different step ranges. And the PCM has a table for airflow amount per IAC step. I'm not sure how the PCM handles the IAC during start up, like if there was a default cranking position and then when the engine kicks over the PCM takes command and adjusts.

Using an IAC from an OBD1 on an OBD2 PCM might be the issue.

Maybe try opening the throttle stop a little. I know on my 96 I can't adjust until it is removed from the car, the throttle body that is. Maybe that is enough to provide air during cranking and all will be well.

You should be able to see a sliver open at throttle 0% closed.

[Daguse5853Z]

If you adjust the throttle stop the computer will just relearn and it'll do the same thing in a couple hours. I have the same problem in my 3400 swapped 95 beretta. Iac nots the problem, I even upped the IAC setting in the pcm with DHP and it didnt do jack. My cats not clogged. I gave up on it. I just give the gas pedal a little feather when I start it and no problem, after it warms up it idles fine and will start fine without and pedal input. I mean maybe your IAC is bad, unbolt it and start your car up and you should see the pintle move back and forth bc the pcm is trying to control the idle.

[Daguse5853Z]

Using an IAC from an OBD1 on an OBD2 PCM might be the issue.

That doesnt make a difference.

You could try leaning out the fuel setting in the pcm, I never got that far bc of time/caring less at the moment but that would essentially be that same as opening the throttle a bit and letting more air in.

[CNCguy]

Did you get this resolved Corey? If not, what percentage of pedal travel to you have to use for it to start?

OBD-I & II IAC are the same.

[TGP37]

I know you can adjust fueling during cranking and have it fade off rapidly. If needing more air, just pull back the fueling modifier. I forget the table name but I think it can be altered in HPTuner.

As for the IAC, thanks for the correction guys. I haven't messed with any OBD-I systems yet.

[Superdave]

the TPS position modifies the cranking pulsewidth, Typically at 0% TPS it's final pulsewidth x 1 ( no change), 25%-62% it's x 2, and above 75% it's x 0 (called clear flood mode).


Adjust the "cranking fuel VS Coolant temp" table and it should take care of it. (Or whatever it's called in your software)