engine hesitation when throttle applied

[NPCe30]

my 318is hesitates when i step on the gas hard
its fine when i ease into it thhough
i replaced the fuel filter but its doing the same thing
i feel like the engine is jus not getting the right amount of fuel but i really dont know whats wrong and i need help
thanksabundle

[jlevie]

Intake leaks or a bad AFM are the most common cause of this. The fuel system can be a cause, but that usually also causes problems at high engine speeds and/or loads.

[b*saint]

j, what's the average time and cost to smoke test a car with a slight vac leak? An hour? I'm going to have to bite the bullet and bring mine in.

[jlevie]

I'd expect to pay for an hour of shop time for a smoke test. When done correctly the exhaust will be plugged and the airbox/AFM will be replaced by an adapter for the smoke input. The intake will be pressurized to 2-3psi and held at that pressure for several minutes. Holding smoke pressure allows for leaks in the block to be found.

[b*saint]

The only thing is I know i have a good size exhaust leak. Will this matter? Or will smoke still come out any intake issues?

[jlevie]

To get a fully valid smoke test, you will have to do something about the exhaust leak. Otherwise it won't be possible to achieve the necessary pressure in the intake. Depending on where the exhaust leak is it may be possible to temporarily plug it with duct tape and band clamps.

[b*saint]

yea its the joint between the muffler assembly and the cat assembly.

[warmsquash1]

my 318is hesitates when i step on the gas hard
its fine when i ease into it thhough
i replaced the fuel filter but its doing the same thing
i feel like the engine is jus not getting the right amount of fuel but i really dont know whats wrong and i need help
thanksabundle

Just out of curiosity, does the hesitation get progressively worse as you drive it, or is it a constant level? If it's progressive, I would look at the fuel pump as the possible culprit. Look at the Bentley manual for the correct procedure to do a pressure and flow test on the pump. I replaced 3 pumps in my 1987 Cabby and one in my friend's 1991 318i... Just my 2 cents... It very well could be the vacuum system or a FPR or even a set of plugs or wires. Just have to check them off the list until something good happens... Good luck!

[NPCe30]

it doesnt get worse as i drive long its jus bad when i work it after 4000 rpm

[jlevie]

This only happens above 4000rpm? In that case the WOT switch in the TPS may be bad.

[blalor]

I'd check the fuel pump. AutoZone will loan you a fuel pressure gauge ($150 deposit, but you get it all back). You'll have to splice into the high pressure line to the injector rail. I had the intake off to do some other stuff, but I temporarily fitted the pressure gauge tee to two longer lines and replaced the 2" section of hose at the injector rail. You should see 43.5 psi (3.0 bar) pretty consistently, from idle to WOT. Pressure should rise "0.4 − 0.7 bar" when you disconnect the vacuum line on the fuel pressure regulator.

You'll spend a couple of hours testing the pump, but it won't cost you a cent if you've got some fuel line kicking around. :)