Randomly losing power

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
I own a 2005 Trailblazer with the 4.2L engine. This problem started a couple weeks ago and has only done it 2 times. Both times happened within 5km of leaving home (driving around 40-50mph) and only lasted briefly for 30 seconds to a minute.

When driving along it just seems to loose power, almost as if your were pressing on the brakes firmly. You have to keep pressing the gas pedal, any attempt at a constant throttle and it slows right down. The trans downshifts to 3rd and just acts as if a alot of drag in the drivetrain.

The first time I pulled over and checked things out and no visible signs of a problem, brakes were cool, pulled away and it worked fine. Second time the GF keep going and said it just stopped doing it. No SES light, engine never had a miss or sputter.

Any know what the problem is or any ideas on where to start trouble shooting at this random issue?
 

Boricua SS

Member
Nov 20, 2011
3,080
Ohio
have you checked out the cat? almost sounds like a clogged cat.. just throwin it out there for ya...
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
What would I look for with the cat to see if it is plugged?

It did it again today on the GF, this time she went to pull over and it quit, restarted and made it a couple hundred yards and quit again. She let it sit for a minute and restarted it up and it drove perfectly fine for the rest of her 15-20 minute drive and back home. Again no SES lights and no pending codes either.

I was talking to a friend that had similar issues from a dirty MAF sensor on a chev halfton he had.

Any other thoughts?
 

triz

Member
Apr 22, 2013
746
Bad Maf or clogged cat could be the issue though they should throw a code.
 

AtlWrk

Member
Dec 6, 2011
674
I thought 2006s were the first to get MAFs.

Easy check for a clogged cat is to pull the upstream O2 sensor out of the exhaust manifold and see if the sluggishness goes away. Seeing as how your problem is intermittent this is unlikely to be conclusive. An auto shop should be able to do a backpressure test for you to rule it out. Clogged cats won't throw a code--they tend to manifest as poor acceleration and power.

My hunch is a fuel delivery issue--possibly a failing FPR?
 

CaptainXL

Member
Dec 4, 2011
2,445
DirtRidinZ71 said:
What would I look for with the cat to see if it is plugged?

You would have poor acceleration during all times. Even in open loop when the engine is cold.
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
After buying some MAF cleaner and then looking for it AtlWrk is right and there is no MAF sensor on it. Going to clean the throttle body today and see if that has any effect on it. IMO it doesnt seem to be fuel related, the engine doesnt sputter more or less just seems to surge. Just like a sensor on a trip.

The problem only happens within the first few minutes of starting it and driving after it sits for a day or two, you can drive somewhere stop for a couple of hours and not have the problem. I dont think it is related but seems to of started after I replaced the Seconday air solinoid valve?

Do these have a coolant temp sensor? I know the one on my tbi 350 causes all kinds of different problems when they go bad.
 

Mark20

Member
Dec 6, 2011
1,630
Assuming you have a Trailblazer of Envoy with an I6 (Tapatalk is not showing me all of your profile and I can't see the first messages in this thread), yes there is a coolant temp sensor. Buried in the block under the alternator.

If it reads cold for too long you'll get a code telling you so. Spiking hot you'll probably won't see on the dash gauge since the computer heavily filters the data.
 

CaptainXL

Member
Dec 4, 2011
2,445
Unless you are comfortable connecting a scan tool and monitoring critical data (like the coolant temp) then I would have a diagnostics shop take a look. You could literally spend a lot of money tracking down something like this yourself. And if the engine is somehow unknowingly misfiring the catalytic converter could be in danger.
 

DirtRidinZ71

Original poster
Member
Apr 12, 2013
12
CaptainXL said:
Unless you are comfortable connecting a scan tool and monitoring critical data (like the coolant temp) then I would have a diagnostics shop take a look. You could literally spend a lot of money tracking down something like this yourself. And if the engine is somehow unknowingly misfiring the catalytic converter could be in danger.

I have no problem with plugging in my obd2 scantool which shows the live run data, the coolant temp is about one of the few numbers that I actually understand. I have no intention on just dumping money on parts without a good reasonable cause, same goes for taking it to any shop here in town. Too much money for me to spend for them to do the same type of guess work. I also know when to cut my loss and take it in somewhere, this newer stuff is over my head.

The worst part is I only have time to scan on the weekends and the problem is not happening often enough to make trouble shooting easy, but it does seem to be getting slightly more often.

Cleaning the throttle body didnt solve the issue, it did seem to smooth out the idle some what. Once I cleaned it and on the test drive it finally lost power on me. I have to correct myself and that it does sputter somewhat when this happens. Today once it started loosing power I let off somewhat and let it coast and it quit. I shifted it to neutral and restarted it, continued on with the drive and this is when it started sputtering slightly with very little power, shift to neutral and it would rev freely, back in drive and no power within I would say 30-45 seconds it cleared up and drove fine. I took it back home, it sat for 5-6 hours before leaving again and no issues then.

The only thing that seems consistant with it is the fact that it has only done it on the first start up of the day and once fully warmed up, the past couple times the outside temp has been warmer and issue happening closer to home. Sun or rain it does not make a difference. It still seems to have good power (we have only owned it for a couple months) and fuel mileage is staying the same.

I will try it tomorrow morning with the scantool hooked up and hopefully see some results, any other numbers on it I should pay attention to? Keep all ideas and thoughts coming.
 

CaptainXL

Member
Dec 4, 2011
2,445
DirtRidinZ71 said:
I also know when to cut my loss and take it in somewhere

We are usually pretty quick about fixing stuff on our engines. You could say we have it down to a science.

However, due to the lack of any further suggestions by us and the fact that you are just sitting there scratching your head...I would say you are at the point of cutting your losses. Usually with an engine that exhibits such obvious issues there is an accompanying CEL or other physical evidence, such as water in the fuel or corroded coils/water in the coils, bad fuel, etc. Have you done even simple things like check manifold vacuum and fuel pressure? We need to know about those results.

I am assuming that because the engine runs fine most of the time that the compression and exhaust system are ok. Therefore the engine mechanicals are ok as well. Wouldn't worry about that.

DirtRidinZ71 said:
this newer stuff is over my head.

So I take it this pretty much means you won't be able to offer us any further diagnostic evidence? Give us some scan tool data to work with. Otherwise time to take it in. OBD2 started in 1996 so it's been around for 16 years. I would hope it's not that far over your head. My .02
 

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