98 GMC Yukon has intermitten miss, misses bad under load ie:going up hill

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thedads
New User | Posts: 2 | Joined: 05/06

Posted: 05/31/06
04:14 AM

I have a 98 GMC Yukon and for the last three years I hve had a problem with random misses. I have had the latest GM diag computer run full diags. on it and it found nothing. If I try to acc. hard going up hills or under load I get a B300 code. If I keep the RPM above 2000 it runs great but let the revs drop below 2k and it misses. I have changed the fuel pump thinking it was low fuel pres. Changed dis. cap and rotor. plug wires.
I'm at my wit’s end I am disabled and cannot afford to just throw money at it.
HELP!!!!!!!!!!!

automotivejtm
Guru | Posts: 1019 | Joined: 03/06

Posted: 05/31/06
09:30 AM

some other possibilites are a clogged cat, bad maf sensor, clogged fuel filter, bad o2 sensor,

Vandy-1
User | Posts: 194 | Joined: 04/06

Posted: 05/31/06
04:55 PM

Some more possibilities: worn distributor,bad vacuum advance,incorrect timing, vacuum leak{s},bad or failing EGR valve

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MikeR
New User | Posts: 34 | Joined: 03/06

Posted: 06/01/06
09:36 AM

Could be the ignition module.

If the misfire is random and jumps from cylinder to cylinder, the OBD II system will set a P0300 random misfire code.

here is some more info I located..

A random misfire code can be set on newer vehicles with OBD II onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhasut into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occuring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code.

Hesitation or misfiring when accelerating. This may be due to a vacuum leak, but it can also be caused by dirty fuel injectors, a weak fuel pump (low fuel pressure) or a faulty fuel pressure regulator. It can also be caused my ignition misfire due to worn or fouled spark plugs, bad spark plug wires, or weak ignition coil.

The important thing to keep in mind about vacuum leaks is that they have the most noticeable effect at idle. At part and full throttle, more air is entering the engine through the throttle opening so a vacuum leak has less effect on the air/fuel ratio.

Look at the info on this page.. http://www.aa1car.com/p0300/index.htm