Ping, limp, and lunge....Sorry long

[gabbott]

97 5.2L Dak 4X4 with cold air K&N, headers, and catback.

Prior to addition of performance mods, the truck ran great. Avg about 17mpg. After instillation of mods, things went down hill:
mpg decreased to a low of 11, now back up to about 16. Power decreased. Both O2 sensors burned out after the instillation and were replaced. The PCM went bad and a used one was installed.

Of late, the truck pings on regular. Recent trip pulling a trailer had to use premium.

Trying to pass a car is a joke. Accelleration is poor and at about 70 mph or 5000 rpm the truck lunges coughes and just about gets me in a head on collision. Than the next time I try to pass it may be fine.

I put in new plugs (3923's gapped at .040) and new spark plug wires. I've run 3-4 injector cleaners through the thing and the dealer says all the sensors are working and the used computer is functioning.

So, my questions are:

1. Does any of the above ring a bell with anyone?

2. Should I pursue a new PCM?

3. What scan tool would you suggest to do my own driveability test?

4. I need to at least get rid of the lunging in passing gear as that is a safety issue, but why with the improved breathing did my mpg get worse?

Thanks to any who take the time to try and point me in the correct direction.

Greg

[Duner]

I would check two sources of possible trouble: The first is the dreaded plenum gasket located at the bottom of the intake manifold. When this leaks, it sucks in oil and that leaves carbon deposits in your combustion chamber. These deposits make it ping. The second is the catalytic convertor. If enough of the oil has gone into the exhaust to screw up your O2 sensors in the past, the cat might be plugged. Generally when the cat gets plugged it actually goes faster at 1/2 throttle than it does at WOT. This also destroys your mileage and severely limits high rpm running. I'm not sure any of this would have much to do with "lunging" but it might give you someplace to start looking.

[Supercharged5.9R/T]

Since you added the pcm, you HAVE to run premium gas in it. Try this and it may solve your pinging probs.

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Anthony Leone
13.27@102.73
99 FR RC R/T

[gabbott]

I did not add a performance computer...just a used standard Dak computer.

Is there a way to check the gasket leak at home or is that a shop procedure?

Thanks

[yamarocket]

block off the Crankcase vent hose (on the left valve cover) but leave the filter in the cover. pull the pcv vlave and put your finger over the pcv grommet hole with the engine running. The engine should build pressure in 2 to 5 seconds. If it builds no pressure, or pulls a vacuum, the pan gasket is leaking. It's a crude test, but it works...
But first, do you have any codes, does the check engine light come on? (is it burned out?) also if you weren't gentle with the exhaust work, it is easy to damage the o2 sensor, but it should set a code...

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If all else fails, use a bigger hammer.

99 Intense Blue Dakota 4wd CC 5.2
ASE master, Daimler/Chrysler Gold Certified Auto Mechanic

[Coolva]

Nonono...
Best way to check (I feel) is to take the air hat off...
Now, with the truck not running.. open the throttlebody (as if you were flooring it)
Get a flashlight and shine down the throttlebody, at the bottom, you will either see a nice shiney metal pan, or an oily residue (thick)

That is the best way to check... just make sure you check as much as you can (not just one spot) shine the light towards the back, and front...
You cant go wrong with this

[This message has been edited by Coolva (edited October 19, 2000).]