Misfires happening on grades and accelrations @ 60+

[poiboy]

Hey people,

I've got a '99 tahoe and I've been searching forums on misfires on the engine, at least that's what I'm gathering. I've had this constant problem and have not been able to solve it. I'm no mechanic, so taking it to a qualified mechanic, they diagnose the engine with the PO300 error, General Misfire. The thing is that the misfire and check engine light usually comes on under these conditions:

going up a grade on the highway with speeds at 50-60+ and/or accelerating on straight/flat highway at 65+. It's re-creatable.

Now, I've seen myriad postings of peoples similar questions and remedies. I guess what I'm hoping for is if someone on here has had a similar experience, and have successfully solve their problem.

I recently had my truck in the shop, and the mechanics suggested to me that when the misfire / check engine light comes on, i should come by their shop. But with the problem usually only coming up at high speeds, how the hell am i supposed to get the truck to the shop and have them diagnose the problem? Well how about a code reader with live recording.. Good idea or no?

Any input is appreciated!

Kama

[blueflamed03]

have you checked plugs, wires, cap,etc for any cracks or splits? Replaced fuel filter to make sure it's not plugged?

[Lowho97]

I just had this problem and solved it after months of searching. Open the hood and go to your driver side where the canister is in front. There are 2 vacuum lines from the canister. The one going to the fuel tank runs along the frame. Follow the line from the canister next to your steering wheel shaft. what happens is the shaft turns and rubs against the line causing it to develop a crack. Either replace the cracked line or cut it and put a rubber hose and hose clamps to seal it.
Keep in mind this was my issue so it may not be yours but its worth a shot. Thanks.

[hapyspaz]

As far as how do you take it to the shop with the engine light on? Haul ass by there honking at high speeds I guess...

No, seriously, anyone that understands a code reader can pull stored codes and what the conditions of the engine were at the time the code popped into the computer (with the right code reader). One of the more common issues I see leading to the random multiple misfire code that you have is the fuel pressure regulator. Fortunately it is a fairly cheap part, unfortunately it is expensive labor, about 2.5 hours to replace.

I would definately check the system first, plugs, wires, cap, rotor, and the evap line Lowho spoke of.

Secondly, I hope the mechanic you took it to didn't charge you for his diagnostic. In the industry if we cant tell you what is wrong, you dont pay us; because we didnt provide a service. Take it back after checking the ignition system, and have them run a fuel pressure test on your engine.

[jimg2347]

My 99 Yukon was misfiring and set a po300 code. Changing the pick up coil in the distributor solved the problem. 30 dollar part and if that is not the cause, call it preventive maintenance.

[the 18th letter]

My 99 Yukon used to do the same thing on steep inclines at highway speeds. It hasn't happened in the last year or two, knock wood, but I didn't do anything to fix it.

[Biggwaukegan]

had misfire going on. it was a combo of bad fuel filter, needed a whole new distributor and a new granelliei mass air flow sensor. may have overdone it with the granellie but so what

[clean454]

mine just started doing this yesterday
and it got bad at one point it like hiccups

[clean454]

well today it got worse ive kinda learned how to drive it
u have to EASE it
so tomorrow im gunna dive into this thing and see if i can figure it out
and a few times i noticed that the oil pressure gauge went to 0 then bounced back up
i looked under the truck no leaks
im gunna search around tomorrow and post my findings