About to purchase an 05 Avalanche - flashing CEL seen during last test drive

So I have made a verbal offer on a private party 05 Avalanche with 71,150 miles on it. Its on consignment and a little corner car lot about 1.5 hours from me. Found out they have had it on their lot for about 3 months with very little to no traffic looking at it. AKA... hasn't been driven much lately. Dealer tells me the owner reports occassionally getting a check engine light for gas cap. Oil pressure gauge it broken (bad stepper motor pretty sure). Truck has an existing extended warranty that is transferable and is included in the sale. Covers engine, transmission, drive axle, 4x4, a/c, front suspension, steering, brakes, cooling, fuel delivery, electrical, and seals/gaskets.

On my first test drive the engine was very sluggish... starting from a stop light I had very little power. Once I got it going it was better but not great. No lights or DIC messages. That was last Thursday.

Went back today to drive again and have local dealership shop foreman go for a drive with me. Today was a much better drive. Plenty of power and acceleration. Just as I expected from this truck (having owned 2 previously). Shop foreman drove and said all seems normal and good. On the way to drop the Avy back off I got a flashing check engine light when on the highway. No DIC messages to go along with it. The flashing would continue at random intervals, sometimes completely stopping for less than a mile. At end of the off-ramp, turned onto the city street and never saw it again after another 3 mile drive to the lot.

Didn't think much of it at the time, figured it was the gas cap thing. Ending up making an offer and it was verbally accepted (no papers signed). Upon further reading this evening, I learn that the flashing CEL is bad news and means the engine is misfiring. Obviously I have not pulled codes...

The engine bay is dirty and dusty. Oil looked a golden color. Didn't check the air filter (no torx drivers with me to open it).

So long story short... is this something I should do running from? I was planning on doing an oil change and new air filter once I get it. I also considered doing plugs and wires too. I've read about cleaning the MAF.

I realize its hard to know without codes... but thoughts?

GO get CODES first.
Have them fix it under their extended warranty first too...

Flashing means big time issues check manual (we have them here http://www.chevyavalanchefanclub.com/resources/2005/index.html )

You do no thave to run you just need to know what it is so you make an educated offer.

Having the car lot doing the consignment get the codes pulled tomorrow morning. That should hopefully tell me more. My fear is with it being inconsistent it will be difficult to diagnose. I put 30+ miles on it in two different test drives with a good mix of highway and city driving. It only reared its ugly head once and for less than 30 seconds...

Not sure how much the seller will be will to do. I already talked him down $1000 off his asking price. I'm getting a great deal compared to NADA and KBB private party value. I have a feeling I could get stuck with diagnostic costs.

flashing CEL is bad bad bad

be very careful

P0300 engine misfire detected 

could be a bad plug ... wires .... coil pack .... got work to do to figure that out ....

p0300 misfire is hard to diagnose... since it means mis fire on any cylinder...
which tends to mean:
Fuel, air leak, bad cats etc...

Specific cylinder misfires P0300X (x is cylinder #) are easier to fix as it is plug, wire, injector, valve. issues.

Now you had misfire and flashing which means it has big issues as it was dumping way too much fuel and was about to (or could have) ruined CATS.

Ask for big deduct on price so you can get it fixed or tell them to fix under their warranty.

Then if they fix drive the crap out of it before buying... need to make sure a driving cycle was doen and not just reset light.

I asked for $500 off the price and still including the warranty transfer. My plan is, if he takes it, to do air filter, oil change, plugs and wires, MAF cleaning, a tank of premium gas and a bottle of fuel injector cleaner and see if it continues.

If it does, then the diagnosis continues...

Sounds like they just did an oil change, as the oil is golden in color.  Can't hurt to do another one though.  I'd suggest going with a full synthetic oil and filter (been doing my own this way since after the dealer did the "first one free" when I bought it.  Mine is an 05 also, 98K miles.

according to the sticker the last oil change was about 9 months ago.... it is almost the to 3000 mile mark since then...

There's debate about the 3K oil change....  personally, I go by the DIC - it tells me when to change the oil, and it's usually around every 8K miles.  I've always seen the 3K change as a way for the dealer or shop to make extra money, and it wastes oil.  The manual even says to change every 7500 miles, unless you drive in really dusty conditions....

I've seen people with Amsoil get 15K between changes....

Snyder80 said:

I asked for $500 off the price and still including the warranty transfer. My plan is, if he takes it, to do air filter, oil change, plugs and wires, MAF cleaning, a tank of premium gas and a bottle of fuel injector cleaner and see if it continues.

If it does, then the diagnosis continues...

Click to expand...

None of that will fix the random MIS FIRE that bad.... IMHO

I wonder if you have intake leak.

In my area I was able to bring to a dealer and for $50 they inspected the truck fully. You may want to do this to make sure nothing pops out at you. The original owner and the lot will likely not help out if you find any major issues later.

You may also want to pull a car fax on it since it could have been in a flood and have wiring issues causing the issues.

If you do go to a dealer just tell them you are getting it from a private party and want to get it checked out.

Rodney

Autocheck history is clean as a whistle on it.

The local chevy dealership  sent a  shop foreman for a drive in it. He said everything looked/felt normal. I had been in the truck for 45 minutes in all driving conditions before it set it off. Short of sending them into a full diagnostic mission, there's not much they can see.

Frankly we haven't been able to reproduce the light.

And ygmn, that thought crossed my mind and I know to spray starter fluid around it and listen for RPMs to jump. I'll be checking that as well. I don't know if the extended warranty would cover that or not. I'm pretty mechanically inclined, so I think I could tackle myself.

I will be picking her up on Thursday. The extended warranty gave me enough peace of mind to go ahead with it!

Snyder80 said:

And ygmn, that thought crossed my mind and I know to spray starter fluid around it and listen for RPMs to jump. I'll be checking that as well.

Click to expand...

I don't think the starter fluid trick works on modern engines like it does the old.

In the old carb days if the there was a vacuum leak it was downstream of the carb - hence the engine was most likely running lean.  The starter fluid if it found the vacuum leak would quickly temporarily fix the lean condition - hence the jump in rpms.

In these engines the closed loop operation with the o2 sensors fixes the lean the condition so the engine isn't running lean.  The starter fluid then makes the fueling go from just right to rich.  Probably won't see a jump in rpms.

Thanks for the correction

That's why I love these forums!

Just got her home! 100 mile drive from the lot to my door.

In those 100 miles the CEL started blinking twice. Once for 3 seconds, once for 6.

3 second occurrence cruise was set at 71 and I was on a decline on the highway. About 15 miles into the trip.

6 second occurrence cruise was set at 65 and I was on a decline on the highway. About 70 miles into the trip.

I was on plenty of other inclines and declines, with cruise on and cruise off. Wasn't going off any other time. Never ran rough, never lost power.

Going to go through and freshen up what I can and keep an eye on it unless someone else had thoughts...

Take it to autozone or advanced auto and have the codes read.  That would be a good starting point.

You may want to perform a Knock sensor replacement. This will likely resolve some issues for you, or prevent them in the future.

Plus it is a known issue for our trucks due to poor design.

You end up pulling off the intake which exposes the top of the motor and the intakes to the cylinders. Be careful not to knock anything into the inlets. In some threads they put rags in the intake ports of the cylinders to prevent dust and dirt from entering. Then you can clean the crap out of the area. If you look for pictures of some trucks you will see this area has a LOT of dirt and gunk in it. Which one would assume is a sign of an intake leak since it would otherwise have to make it through your filter.

Replace the sensors with The Delphi sensors your truck came with. This preventative repair should be relatively easy and is cheap if you get the parts from RockAuto or some other discount parts location. Plus when you are done you shouldn't have to worry about the knock sensors ever again, your intake gasket has been replaced and is no longer a point of contention for the misfire and you cleaned the crap out of everything. (Of course remove the rags before you reassemble.)

Rodney

Once this weather breaks I had planned to do the intake manifold gaskets. I will definitely plan to do the knock sensors while I am at it.

Haven't seen the light at all since I brought her home. Had codes checked again and still only P0300 stored.

Loving my new truck and coming up with a growing "to do/wish" list!

There is a TSB for the knock sensors that talks about taking the plastic plug that goes on top of the sensors to put high temp silicone around the plug. Some people decide to put the silicone all the way around the plug to prevent water from going into the plug.

Rodney

Snyder do a plug change and use AC Delcos, second with the engine running at nite take a spay bottle and mist the engine- if you see sparks the plug wires are shot.

A tip on the 5.3 it does not like Bosch or E3 spark plugs or "multi-tip" plugs. Really the Ac is the best to use.

You could also have an intake manifold gasket going bad.

Clean the throttle body and MAF too.

Avalon

Well I've had her a week now and put about 200 miles on. Mostly in town. A little bit of highway. No CEL at all. Today I open up the air box to check the filter. Decide to change it. Put it back together to drop my kids off. On the way to the auto parts store after that... decide to take the highway. Light flashes at me. A LOT more than it ever has. Change air filter, and go get oil changed at the dealership. I can feel a difference in the acceleration.

Decide to do out on the highway to check it out again. As soon as I hit 65, it starts flashing. After about 30 seconds the CEL stops flashing and comes on steady. Had not yet seen it on steady  .... It flashes again a few times and goes back to solid. Stays solid rest of the drive.

Get codes checked again at AZ. Still only stored code is P0300. I did not have them cleared previously, so I do not know if this is a new code or not....

Went ahead and bought some AC Delco plugs and wires. Will be changing them once weather cooperates somewhat. May go get codes cleared tonight so that I know if theres anything new.

But just like before... no lack of power, no noticeable skips, not running bad at all. Only had been doing it previously on the highway.

I'm starting to get an uneasy feeling and I don't like it 

you need to get it scanned by a real code reader. one that can read any pre light codes set in the memory, should tell why the CEL came on, beyond the random miss.

dealer/shop with tech2 or someone with HPtuners or maybe EFI live

I have looked in mine with hptuners and there are around 20 things at any given time. most don't mean a thing

I have en 05 AV 1500 and I had a similar issue to this after changing my intake gaskets with a knock sensor replacement.
It started out with the flashing engine light and a slightly rough idle. This would occur from time to time and the light would go out. Over 2 months, the idle got worse and the CEL light came on steady with the P0300 code associated. Thinking I bungled the intake gaskets, I replaced them yet again. The problem got worse and the several codes that appeared led me to my passenger side pre-cat O2 censor.
Once I replaced the O2 censor, the CEL has not come back and the engine idles normally. Getting a code reader that can read pre-codes would be a good idea and might save you some frustration.