Acceleration issue

[blisted]

Update 6/25/09:
Purge Valve/Thermistor replacement seems to (finally) cleared the code.

Codes cleared, thermostat replaced. Planning on checking fuel pressure/compression sometime soon to identify any other possible issues with cat going bad before replacement.

 

[blisted]

Update 7/30/09:

Ran various tests ranging from resistance to compressions tests. Results are as follows. Replaced passenger side of plugs and checked older ones to see if any issues, nothing obvious there.

Still have some odd issue of a slight engine hesitation after initially starting, and just slightly pushing the accelerator down. After she warms up after say 5 minutes the minute accelerator press issue is no longer present.

Compression: I am venturing to say these may be off a tad due to incomplete connections.
Cyl#si
4:155
3:145
2:135
1:120

Vacuum:
Engine idle few seconds after cold start: 19psi up and down to/from 19.5psi slowly.
Idle after 10 minutes: 20 psi
Punch on gas with fast release: drops from 20psi down 5-10psi (couldnt complete read gauge so estimating) and ramps up to 24psi, back to 21 psi steady.



Will try the compression tester in the front o2 sensor and rear to compare tomorrow see if the cat is definitively bad.

 

[Mark_88]

Although your compression is pretty good, it is not within the recommended 15% range...even though it is not the cause of hesitation...

Since you are getting the hesitation after doing a bit of work, I'd say it's time to look at the less obvious things...like fuel pressure...a vac tester can be used to test fuel pressure but you will need to put it directly into the line to see if you've got a pump or line problem...like a piece of hose that is crimped because it was replaced with rubber hose...or simply the pump is going south...or get a fuel pressure regulator with a guage on it so you can monitor it during driving...

 

[blisted]

yeah I've been wanting to check the fuel pressure, I've been tossing the idea around that my fuel pressure regulator is done.

One thing I meant to note is right after starting there is a smell of fuel (like running rich) for a minute before it dissipates.

How do I use the vac gauge to check the fuel pressure exactly? If capable ill check that out today with the back pressure.

 

[blisted]

Update 8/1:

Well threw the compression tester on the front and back o2 sensor spots to see if I could diagnose any pressure build ups and did not get a reading in either case. That really threw me off there....Should have seen some kind of pressure no?

Checked the vacuum on the EGR valve and its within specs (< 1 hg).

Disconnected the air intake at the filter, and felt what kind of air it was sucking and it felt weak, no real pull or anything, almost choked it out by putting my hand in way of the weak drag.

 

[Mark_88]

Update 8/1:

Disconnected the air intake at the filter, and felt what kind of air it was sucking and it felt weak, no real pull or anything, almost choked it out by putting my hand in way of the weak drag.

The air intake at idle is fairly weak...if you rev it up you should get better suction...if you don't you may have a vac leak...but you did say the vac was testing ok...

To test the fuel pressure with the vac tester you simply put the connector into the fuel line...when you turn the key the pump kicks in and you should get a reading...not sure what that would be because I don't have my manuals handy...

 

[blisted]

Update 8/7:
Determined that the cat has a hole/break somewhere underneath the heat shield, which explains not reading any back pressure. Assuming this may be why I am smelling a rich fuel smell after starting up. I am wondering though if the cat is definitely leaking like this would that cause mis-readings on the rear o2 sensor or some other troubles that would cause the high speed acceleration issue?

 

[Mark_88]

The cat should be after the O2 sensor so a leaky one should not affect readings...but may explain why you smell the rich fuel...and if you have little or no back pressure that might give the engine cause for hesitation...but I don't know because I ran my 2.3 with only the header and it ran fine...well, it ran...but there were other issues that needed attention so it was dying if I tried to rev it up...

 

[blisted]

update 8/20:

Vehicle took a dump on me yesterday and put er in the shop today to check the exhaust. Evidently the cat does not appear to be issue but possibly a result. Saying I'm possibly running lean causing these stumbling problems, so they are running some diagnostics now. To be continued when more info comes to me....

just sucks having a money clock ticking while I twiddle my thumbs...