BigJames24

98 camaro z28 ls1 won't start after replacing fuel pump. I had a cheap ebay pump that I replaced with a Walbro 255lph pump along with a new fuel pressure regulator and fuel tank pressure sensor. While trying to start the car I can hear the fuel pump priming and the pressure reads at just a little over 70lbs. I know the ls1 usually runs around 60lbs of pressure so could to much pressure be flooding the engine and stop it from turning over? I don't think so but I would appreciate any input. Thank you!

BigJames24

A code did come up at first. P0452 evaporative emission control system. After I cleared it, it never reappeared.

Paul Bell

iTrader: (9)

Did the engine even try to start? If flooded, hold the gas pedal on the floor and try starting again. This'll put it into "clear flood" mode.

Have you checked for spark?

BigJames24

Yeah it was trying to start. It has new wires, plugs, and a new battery. Maybe I should check the ignition next?

Paul Bell

iTrader: (9)

If it's trying to start, you have spark. Smells like fuel?

BigJames24

Can't really tell because the whole car smells like fuel due to the trap door in the trunk. Fuel filter is also new.

Mods89

After cranking it, pull a plug and check to see if it's wet. If it's getting fuel, it will have gas on it. Then if it does, check for spark.

BigJames24

I held the pedal and the car started but the rpms were really high in park. I think it was around 2300-2500 rpms. And then the codes P0121 & P0123 came up. They're for the throttle/pedal position sensor.

BigJames24

The car will only start now if I hold the pedal to the floor and like I said before it runs at a high rpm. Could whatever is causing my car not to start properly be affecting the throttle position sensor? Just because the code came up doesn't mean that the sensor is bad right? I don't want to replace anything else for no reason.

Paul Bell

iTrader: (9)

Now we're getting somewhere.

After it starts, you let go the gas pedal and it idles that high?

Check all the plugs to the throttle body.

Very high idle can also be caused by a vacuum leak (false air) like a hose left off such as for the brakes.

BigJames24

Well I did just take off the intake manifold a few weeks ago but the vac line is the back was put back on along with the brake booster hose...and the throttle body has all the lines properly connected to it. If the manifold is not torqued down to specs could that keep it from starting? Or running the way it is once it starts?

codyvette

iTrader: (24)

Yes. Nonuniform bilt tension can cause air leaks and break the intake.

Paul Bell

iTrader: (9)

OK, sounds like the work on the engine itself is what's causing your issues. As you had good fuel pressure and the engine ran, your work on the fuel pump is good. Now, find what you screwed up elsewhere.

I was talking about plugs as in electrical plugs to the throttle body.

BigJames24

The codes for the throttle positioning sensor did come up but I think it's because the car is running at such a high rpm not because the sensor is bad. Other than that everything looks as though it should be.

Paul Bell

iTrader: (9)

You must have a vacuum leak. When the engine has extra air into it, the PCM assumes the throttle is opened and without an open signal from the TPS, it'll report that the TPS must be bad.

Recheck all your hoses. How tight did you make the intake manifold bolts?