Trying To Solve Egr And Misfire Problem

lunytnz · January 15, 2011

For a few months now, I've noticed what felt like misfires while at cruise or slight acceleration, but no codes

I asked a mechanic about it and he suggested I unplug the EGR to see if I noticed any difference. With the EGR valve unplugged, it ran smoother. Finally, this week, the misfires were more noticeable and it set codes: P0300 (random misfire) and P0405 (EGR circuit).

From a search on the EGR, others suggested trying to clean it. So, I did that today, but a quick test drive shows I can still feel the misfires The end of the pintle is a T20 screw--is that something you can actually take apart? All I did was hold the pintle in a bit and squirt generous amounts of intake cleaner in it, and then scrub what I could (the outer part) with a toothbrush. Is there any better way to clean the EGR? Or, now that I've given that a try and it didn't work, should I just consider it time to replace the EGR?

BTW, if you need to tackle the EGR job, there's hardly and easier do-it-yourselfer job. It's right on the top-front of the engine and you just carefully unplug it and undo two 10mm bolts and it pops right out. Be careful not to drop the bolts (almost did) and watch out the gasket doesn't fall down behind the waterpump (that I *DID* do... sigh, but got lucky and fished it out from under the truck).

[email protected] · January 15, 2011

Do what I did, put a piece of tin between the egr and the deck it's on and buy another gasket so you can seal both the egr and the deck against the tin piece. Once it's all back together plug it back in. No more engine light, no more stupid egr, and by looking at it you can't tell it's blocked if you cut the tin to it's curvature. Egr is one of the worst things chevy did to these engines, it was so bad that in 2002 they didn't put egrs on them anymore.

233monte · January 16, 2011

You could have 2 seperate problems. Egr problems are generally felt at idle. If the egr was stuck open it would idle very rough but smooth out under accel and cruise.

lunytnz · January 16, 2011

I think there's a real possibility of that, 233monte, since it seems to idle fine. I only notice the misfires at cruise and under mild acceleration. If I give it more throttle, I don't notice the misfires. I was thinking it was stuck open, which was creating a bit of a lean condition and creating the misfires. But, idle hasn't been much of a problem. It's been getting worse, to the point it finally set codes, any other likely culprits? I have a cable and software to monitor the OBDII data, everything else I could see seemed normal.

2001Silverado364, I like the idea of blocking it off, too!

lunytnz · January 31, 2011

Since cleaning the EGR didn't do the trick (no noticeable difference, really), I went ahead and replaced the EGR. Immediately after I replaced and took it for a short (around the block) test drive, it seemed to run smooth, so I thought all was fixed. However, when I started off cold the next morning, it was misfiring badly--MUCH worse than before I changed the EGR. I unplugged the EGR and it seemed to run much smoother while warm, but the next day, it was running really rough again, especially when cold and going up a hill.

I'm not sure what to think now. Any ideas? I suppose it could be an injector and it could be some other way that air is getting in after the throttle body (but I just had the intake manifold replaced this past summer because it was leaking--both coolant and air, I think).

I'm going to take the new EGR off to see if there's anything obvious stuck in it. If it looks clean, I may block it off just to see if that makes a difference.

Thanks for any help!

brianf60 · February 1, 2011

Time to check and see if the exhaust is plugged. If it is not flowing enough it will cause mild misfires. Do you have access to a scanner to see what cylinders are mising.

lunytnz · February 1, 2011

I have a cable and some OBDII software, but not a typical scan tool. I may need different software to tell which cylinders are misfiring. The code indicated random misfires, though. Tonight, I cut a piece of tin and used it to block off the EGR port, so we'll see if that makes any difference on the drive tomorrow. Again, on a short test drive after blocking it off, it ran pretty smooth (but I think the real test will be when it's cold).

lunytnz · February 2, 2011

This morning, it ran smooth while cold and seemed to be 'normal' on the drive in and back from work (about 20 miles). I put the old EGR valve back on, since it wasn't going to be accomplishing anything, anyway. So, now I figure the only risk is getting some EGR codes if the EGR isn't responding properly to ECM commands (that is, it was on it's way out, anyway).

At this point, I'm thanking 2001Silverado364 for the idea! As long as no other side effects occur, I'm good to go!

lunytnz · February 3, 2011

Well, it was wishful thinking! Today, even though it was running smoothly, the Check Engine light came on. I checked it out tonight and discovered a new code: P0401 (Insufficient EGR flow). Info on that code also mentions a pressure sensor (DPFE) that could possibly be related to my original problem (maybe a stretch).

I cleared all the codes and will see what happens on the drive tomorrow, but it seems to make sense that blocking off the EGR port would create an insufficient EGR flow (duh!). BUT, it's running GREAT with the EGR blocked! So, does that sound like the new EGR valve I got isn't working right?

GMstrong · February 3, 2011

Is there a way to see if it working correctly pull it off and spray some kind of cleaner in the square then if it comes out of the circle port its bad.At idle that egr valve should be shut closed then upon acceleration it begins to open.

lunytnz · February 4, 2011

I'm not sure how to test the new part to see if it is bad. Again, today, it ran great but set the P0401 code (insufficient EGR flow), so I guess I could try taking the EGR back and try another one. Other than failing my next emissions inspection and not being able to tell if some other problem has turned on the check engine light, I don't have a problem running it as-is.

GMstrong · February 4, 2011

You check egr valves by spraying gum cutter in the square port then if it comes out of the circle port with the rod its bad.Sorry my lost post i messed up with spelling

lunytnz · February 5, 2011

Now, I'm confused Today, it started up fine, cold. Then, about a half-mile away from home, it started stumbling pretty bad again going up a hill (kinda like right after I put the new EGR valve in). It ran more smooth once it warmed up, but still some noticeable stumbling/misfires. I checked codes tonight and I have a P0300 (random misfire) and P0401 (insufficient flow). I plan to take the EGR off this weekend and see if I can spot anything.

Thanks for clarifying, GMstrong. I'll try that test this weekend.

GMstrong · February 5, 2011

Misfiring could be a verity of things.Bad coil pack,Fouled spark plug,Wrong Gap size on spark plugs.And the list goes on.You might be having an ignition problem.If you put the new egr valve back in and it says insufficient flow from egr then you know something far from right.

lunytnz · February 5, 2011

Well, I'm pretty sure I created the insufficient flow problem by blocking off the EGR :-)

The confusing part is that, after blocking off the EGR, it ran like a top for 2 days (even though it was setting the P0401 code, which made total sense). The 3rd day, it started stumbling hard again going up hills (with the EGR blocked off).

And I hear ya that there could be all kinds of reasons for misfires. Not to mention more than one thing contributing to them. This all started months ago when I could feel the misfires, but it didn't set a code. Eventually, it got bad enough to set a P0405 (EGR) code. I had already suspected the EGR, so that's when I replaced it. It didn't run any better with the new one, so I blocked off the port, and then it ran great.

So, it's *possible* the P0405 code was just a glitch, and there's been some other cause of the misfires all along, but that would surprise me at this point.