Engine engine bogs down over 2500 rpm

wmburns said:

The EVAP line goes from the right hand fender well to a vacuum port. For the 1996-1998 model year the EVAP line goes from the the throttle body to the Purge flow sensor, then onto the purge solenoid. From there it goes into the right hand fender well.

Didn't you buy a new EVAP solenoid and purge flow sensor? It's on the same vacuum line.

From the picture it looks like the larger vacuum line with the red stripe.

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wmburns said:

Two of the parts circled are for the EGR system. The upper right part is the DPFE sensor. The part near the middle is the EGR vacuum solenoid.

As stated very early on in this thread that excessive EGR flow can cause loss of power. The key to this whole problem is to figure out WHAT changes when the problem occurs.

In the same way as trouble shooting an EVAP problem the way to trouble shoot a suspected EGR problem is to monitor the DPFE sensor. Looking for an increase in EGR flow when the problem occurs.

The low tech approach is to disconnect and plug the EGR vacuum line. Does this improve the issue? The limitation of this method is it won't work IF the EGR valve is stuck open. For this a manual block off gasket between the EGR valve and the TB is what the doctor ordered.

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wmburns said:

The vacuum hoses in question control the EGR system. When disabling the EGR system and not getting any improvement, this tends to say that EGR is not your issue.

How about the EVAP system? Have you disconnected and plugged the EVAP line?

In all of this check this and check that, it still seems to me that some "basic" information is missing. To me this seems odd considering that you do have access to advanced ODB2 data. For example:

• What do short term fuel trims bank1 and bank2 (STFT) do just before and after this problem occurs?
• What do LTFT's do when this problem occurs?
• How does the timing advance change as this problem occurs?

OBTW, what have you done to rule out a blocked exhaust?

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wmburns said:

I'm still bothered by the obviously unstable ECT sensor. 118.6 is why too low. This will affect HOW the PCM alters the AF mixture. As part of the same run it obviously points to a problem if part of the same run.

The only way I know of to positively rule out a blocked cat is to measure the pressure before and after the cat. A basic health check can be done by removing the O2 sensor and measuring the pressure at the O2 bung hole.

Another exhaust health check is the measure the intake manifold vacuum. It will show up as low vacuum at idle. But will have a decreasing unstable vacuum under stable RPM (say 2500 RPM)

In the data dump above note the STFT. The PCM is adding fuel at a large rate. Also note that it's the same on both banks. What we don't know is if this is the problem or a symptom of the problem.

If this were my car I would "record" a running list of:

• RPM's
• MAF
• O2 voltage bank 1 sensor 1 and bank 2 sensor 1.
• STFT bank 1 and bank 2.
• TPS

Drive the car until the problem occurs. This will crate fairly large data set. This is where having good Excel skills will pay off. The key is to graph the data from a common origin point so that trends over time can be seen. IE which happens first? Or is there a build up until the STFT limit is reached?

Specifically I want to know how the O2 sensors are switching just before the problem happens. In fact pay close attention to any sensor that changes right before the STFT go through the roof.

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wmburns said:

The only way I know of to positively rule out a blocked cat is to measure the pressure before and after the cat. A basic health check can be done by removing the O2 sensor and measuring the pressure at the O2 bung hole.

Another exhaust health check is the measure the intake manifold vacuum. It will show up as low vacuum at idle. But will have a decreasing unstable vacuum under stable RPM (say 2500 RPM)

In the data dump above note the STFT. The PCM is adding fuel at a large rate. Also note that it's the same on both banks. What we don't know is if this is the problem or a symptom of the problem.

Refresh my memory. Has the fuel pressure been monitored why driving?

If this were my car I would "record" a running list of:

• RPM's
• MAF
• O2 voltage bank 1 sensor 1 and bank 2 sensor 1.
• STFT bank 1 and bank 2.
• TPS

Drive the car until the problem occurs. This will crate fairly large data set. This is where having good Excel skills will pay off. The key is to graph the data from a common origin point so that trends over time can be seen. IE which happens first? Or is there a build up until the STFT limit is reached?

Specifically I want to know how the O2 sensors are switching just before the problem happens. In fact pay close attention to any sensor that changes right before the STFT go through the roof.

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wmburns said:

Glad to hear that. This is a good lesson in what can be done by testing and going where the evidence points. It also confirms that sometimes a new part isn't a "good" part.

Did you find any evidence of WHY the recently replaced fuel pump apparently went bad sooooooooooo quickly?

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