Acceleration Problem

I've spent hours on the 'boards looking for an explanation that fit my problem. Here to share the result of the process:

Problem: car starts nicely, idles well, warms up properly, drives off smoothly. However, on strong acceleration it bucks, and tries to die. Back off, runs fine.

Tried my repertoire of MAD, TPS, O2, Fuel, plugs, no solution.

Then, my son-in-law top mechanic said, "See if a trottle blip drives MAF output up." That was it. MAF bad.

Explanation. Car gathers speed rapidly, no problem. But Lambda Sond is in control. Then, when quickly, strongly accelerating, goes lean and tries to die. Missing: no throttle pump. Lambda Sond cannot respond fast enough to give the burst of fuel required, as would a throttle pump. That's the job of the MAF, to tell the ECU to shoot in more fuel. QED.

FYI, the lambda doesn't have any interaction with acceleration on an EFI engine. The mass air sensor should see and respond with more fuel. However, the initial extra fuel comes from the change in vacuum applied to the fuel pressure regulator. That gives the extra fuel needed till the mass air sensor response is seen by the ecu.

With a fuel pressure gauge you should see a short rise in fuel pressure as the vacuum change provides the extra fuel. I would suggest you do a fuel pressure check just to be sure the regulator is working.

The fuel pressure regulator serves to keep the fuel quantity stable when the throttle is opened, so engine management can rely on exactly how much fuel will pass through the injectors when the opening duration is increased by the ECU in response to the MAF. The increased fuel pressure is balanced by the increase in manifold pressure sensed by the fuel pressure regulator, so the fuel amount is exactly the same. Without the AMM's response to the increased air, the fuel amount would not increase at all.

dl242gt said:

However, the initial extra fuel comes from the change in vacuum applied to the fuel pressure regulator.

Click to expand...

In carburetor days: Symptoms of a Bad or Failing Accelerator Pump

An accelerator pump is a component on a carburetor. ... The accelerator pump is responsible for providing the momentary additional fuel needed under heavy acceleration conditions. When the pedal is suddenly pressed, the throttle will suddenly open, immediately adding additional air for additional power.
...
Rough acceleration
.
Engine sputtering or stalling
===========

RE: OP's Explanation - Better check rail pressure at idle, then punch it.