Misfire?

[SGC]

I have a 2003 Avalanche that just started misfiring. It idles fine but around 25 MPH, the motor starts shaking it then feels like someone is holding it and finally lets go and I can get to speed and seemingly does fine. It is throwing multiple codes which I posted a picture below. The spark plugs and wires were replaced 3,000 miles ago with GM AC Delco plugs and wires. When doing them, I noticed some bolts were broke on the exhaust manifold. Lately, I have been having a whistling sound on acceleration when it is cold outside. Is it possible this is a blown exhaust manifold gasket?

 

 

[carnau]

More than likely it is a bad fuel pump. But we should do a little more checking because it could also be a clogged converter or other things. First, If you have a fuel pressure gauge you need to be running between 55-60 psi of fuel pressure when at idle or driving. If you don't have a fuel pressure gauge, You can get this one pretty inexpensive and it's always good to have one if you do you own repairs. ( https://amzn.to/2V87yl9 ) If you don't want to purchase one, you can go to the loaner tools at your local parts store and pick on up. But before replacing any parts lets diagnose it further. Let me know that number and let me see what I can do for you.

 

 

[SGC]

I'll have to scare up a fuel pressure gauge. Probably won't get to it until the weekend. The whistling I had been hearing before had me thinking vacuum leak. I kind of hope it is the cat converter because I have been wanting to put a new exhaust on this truck and this will give me an excuse to do it. 

[SGC]

Now that you had mentioned the fuel pump, I do recall that the fuel pump would make a loud whine especially when cold. 

[carnau]

2 hours ago, SGC said:

I'll have to scare up a fuel pressure gauge. Probably won't get to it until the weekend. The whistling I had been hearing before had me thinking vacuum leak. I kind of hope it is the cat converter because I have been wanting to put a new exhaust on this truck and this will give me an excuse to do it. 

Well you still don't want it to be the converters, you don't remove the converters when you do an exhaust job. Unless you're doing headers and removing them all together. lol

 

I'm pretty sure it's the fuel pump by the codes. But I don't believe in throwing parts at a vehicle and not doing the proper diag.

 

If it is the pump. I believe in going OEM. The Pump you have in there now is probably the pump that came in the vehicle and it has lasted a pretty good while. lol. If you go with an aftermarket pump you may get a few years... MAY. lol

 

But, on a side not. The pump you have in that is a delphi pump. This is actually the exact pump in your vehicle at a fraction of the cost. https://amzn.to/2GUvUuV

[riverbanks]

If both sides had broken bolts,a possibility,air leak can cause 02's to go lean,and can you check MAF output,that's also a possibility

[SGC]

10 hours ago, carnau said:

Well you still don't want it to be the converters, you don't remove the converters when you do an exhaust job. Unless you're doing headers and removing them all together. lol

 

I'm pretty sure it's the fuel pump by the codes. But I don't believe in throwing parts at a vehicle and not doing the proper diag.

 

If it is the pump. I believe in going OEM. The Pump you have in there now is probably the pump that came in the vehicle and it has lasted a pretty good while. lol. If you go with an aftermarket pump you may get a few years... MAY. lol

 

But, on a side not. The pump you have in that is a delphi pump. This is actually the exact pump in your vehicle at a fraction of the cost. https://amzn.to/2GUvUuV

If it were the cat converters, I would put on a new cat back system while I was rooting around down there. This is the first truck, or V8 for that matter, that I have owned and want it to sound like one but have never been able to justify the costs or work.

 

I go back and forth between vacuum and fuel pump. It idles fine. Under acceleration from about 20 MPH to about 40 MPH the engine shakes from a miss and has a lack of power. While this is happening, the check engine light flashes instead of staying on constantly. Once I reach cruising speed, it seems ok. When the outside temperature was real cold, I would hear a whistling sound coming from under the hood before I had this issue. It would whistle when I would accelerate. Also on the real cold days, the fuel pump would whine pretty loud after the car had been started. I may have access to a smoke tester first so I may check vacuum first. Going to clean the MAF sensor. I doubt that will do it but it doesn't hurt to clean it.

[carnau]

2 hours ago, SGC said:

If it were the cat converters, I would put on a new cat back system while I was rooting around down there. This is the first truck, or V8 for that matter, that I have owned and want it to sound like one but have never been able to justify the costs or work.

 

I go back and forth between vacuum and fuel pump. It idles fine. Under acceleration from about 20 MPH to about 40 MPH the engine shakes from a miss and has a lack of power. While this is happening, the check engine light flashes instead of staying on constantly. Once I reach cruising speed, it seems ok. When the outside temperature was real cold, I would hear a whistling sound coming from under the hood before I had this issue. It would whistle when I would accelerate. Also on the real cold days, the fuel pump would whine pretty loud after the car had been started. I may have access to a smoke tester first so I may check vacuum first. Going to clean the MAF sensor. I doubt that will do it but it doesn't hurt to clean it.

Yeah, What happens is the fuel pump looses volume when accelerating when the vehicle needs more fuel. It maintains at higher speeds. We just need to know what the fuel pressure is doing to proceed. 

[SGC]

Is it possible the filter could be plugged? My understanding these don't have an inline filter so I guess I would need to pull the fuel pump anyways. If I can commandeer a fuel pressure gauge, I may just bite the bullet and buy one. Wouldn't hurt to have.

[SGC]

I also haven't looked, but I assume there is a fuel pressure port under the hood where I would attach the gauge to? I may just run out and buy and/or rent one tonight.

[mjm-1957]

if its a 2003 it has an inline fuel filter by the ABS unit on the rail under the drivers door.

[SGC]

Interesting. It is a 2003. I bought the truck a year ago. When I buy a used vehicle, I go and replace filters, fluids, plugs, and wires. When I went to the part store to buy a fuel filter, they told me it was in the tank. I decided not to bother. I will replace the fuel filter. Regardless if it is the issue or not.

[carnau]

2 hours ago, SGC said:

I also haven't looked, but I assume there is a fuel pressure port under the hood where I would attach the gauge to? I may just run out and buy and/or rent one tonight.

There is a fuel pressure gauge adapter on the right fuel rail on the side of the manifold. Very easy to access.

[riverbanks]

Take a look under there,parts store correct? you never know,too much uninformed lately, bummer,got too take the bull by the horns

[SGC]

Ok so I did a no-no and threw some parts at it. Had my neighbor look at it as well who is somewhat of a backyard mechanic. Sprayed some cleaner to check for vacuum leaks. Noticed the front of the intake appeared to be leaking. Did a water test and it was sucking it in and spitting out steam from the tailpipe. He also heard the same whistling I did. Just got done throwing an intake gasket on it. This engine is pretty easy to work on. The whistling is gone. It passes the water test. The codes are gone and don't come back, but it still has a miss. The intake gasket was bad so it needed to be replaced anyways. Looks like I had two separate issues. Too tired to mess with it further tonight. Tomorrow morning I will test the fuel pressure. Putting on a new fuel filter. I did clean the MAF sensor. The codes may have been related to the intake and not the miss. The fuel pump is noisy when cold so I'm leaning towards that.