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Possible Trailblazer fuel pump issue (previously catalytic)

I recently purchased a 2005 Trailblazer (4.2 l) with less than 80k miles from family. So I’m pretty familiar with the history. Unfortunately that history involves a misfire code last year and my dad taking it to the local guy he knew in town. He changed the spark plugs and cleared the code. It came back. So my dad took it back and the guy poured a quart of ATF in the gas tank, cleared the code again and told him to see if the code comes back. It did, of course and now it had been being driven with misfires for weeks. So I checked the code and it was a cylinder 3 misfiring. So for $60 and 10 minutes, I replaced the coil and all was well. Well, until recently when I started noticing power loss on highway inclines. Sometimes I can push it to the floor without it going any faster. Other times on incline, it just seems lacking in response/sluggish. Otherwise it seems to drive fine but I’ve also started noticing a low rumble coming from underneath the mid-rear of the vehicle. Not super loud but I’ve noticed it. No rattle but it does get louder and can be heard in the car when accelerating on the highway.

I’m limited in experience, knowledge and tools but have been tackling increasingly harder projects with my cars with success (not that any have been all that hard). I did the only test I had tools for and I’m not even sure I did i correctly but I checked inlet/oulet temp of the cat with an infrared gun. I drove the car around the block, then parked in my driveway and had my wife keep it a 3k rpms while I checked the temps. I got 500 inlet and 400 outlet. Checked it twice. From reading online, I understand this indicates a pretty obvious problem. But then why don’t I have an engine light or code? I’ve been reading and watching a ton on this the last few days and it lead me down a path towards the cat and these temps seemed to confirm a problem. Does it sound like that’s the case even without an engine light/code?

I researched the procedure for replacing the cat. It seems I have multiple options but I’m seeing some issue with each one.

I considered the lacquer thinner in the gas tank just as something cheap to try first but I’m figuring if the cat clogging is from the misfires, wouldn’t it most likely be pretty baked/welded on? I’d love to remove it and see if I could clean it by soaking but from my research, it sounds like I’d need to cut the pipe or remove the transmission crossmember to get it out. Cutting the pipe means I can’t put it back (or does it?) and removing the cross member makes me nervous, being a novice.

I see there are universal cats that say they work with my vehicle and not very expensive. I tried watching youtube videos on these installs but all the ones I could find skipped the actual installing moments. Is it really just as easy as cutting out the old cat and clamping this one in with a piece of make-up pipe?

Then there’s the direct fit. But now I’m back to the issue of needing to remove the crossmember. This will also cost about 2.5x as much as the universal instal and approaching more than I want to spend on the vehicle. If I knew it would take care of the problem and I could accomplish it, then I’d do it. But neither is guaranteed. I’m also concerned about needing to remove the 15 year old flange bolts that are way up in an awkward place so I’m nervous about breaking one.

Thanks in advance for any insight/help anyone is willing to offer. I’m pretty set on attempting something, I just haven’t decided what.


I removed my TB cat when I pulled trans. It unbolts with little effort.

But would I be able to remove and install a new one without removing the trans support member? I’d really rather not risk screwing something else up while trying to fix this issue. What year is your TB?

I haven’t been able to find a video of cat replacement for my actual TB year but other videos indicate I can’t remove the cat without cutting or removing the cross member.

A transmission crossmember is not rocket science to remove and replace. I’d be surprised if the pipe and cat don’t just slide out with a little wiggling and rotation.

That ATF in the gas tank combined with a failure to fix the misfire likely destroyed your cat. Don’t let that “local guy” touch your car again.

Yeah, I know it would be easy to remove and replace but my concern is my lack of knowledge and understanding of everything under there and maybe not supporting the tranny properly while I’m working. I’m kind of surprised it wouldn’t be able to be pulled out, too. But similar vehicles of surrounding years that I found said it couldn’t be done without cutting or removing the crossmember. But I’ll look back under mine and see if I think that’s the case.

The parts stores around me are showing universal cats for $100-150 and a direct fit for $300. I’m leaning towards buying the universal to try first. It says it’s 16-in. I measured and once I cut out the old one, it should leave a 14-in gap. I’m thinking I can clamp this new on in without needing to add any pipe. If it all goes that smoothly, then I should be good and for pretty cheap. If it doesn’t, then I’ll return the universal and buy the direct. The other thing influencing that decision is that the universal can be picked up today but the direct needs shipped. I’m off tomorrow and would really like to get this done before I need it for work on Tues. What kind of damage is being done driving it like this?

Is it odd that I don’t have a light or code?

Yeah, that’s what I figured happened once I started reading about it. He’s dead, so he won’t be touching it anymore. Not that I’d let him.

The cat is between trans/frame rail. It’s tight. I would say removing trans support is required. Put it on ramps. Use jack to hold up trans. Drop crossmember. Pretty easy.

So far, I haven’t seen any conclusive proof that you actually fixed the misfire(s) . . .

Just because the check engine light isn’t on doesn’t mean much

I would perform a compression test on all 6 cylinders before spending any more money on this truck

You might be surprised at the results, which you’ll hopefully post

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The codes kept coming back the 2-3 times the mechanic cleared them and after I replaced the 3rd cylinder coil (code was for 3rd cylinder every time), it never came back. I know it’s not conclusive but is it not likely the coil was the issue?

I’ll pick up what I need tomorrow to do the test. Will report the findings.

Would you say the heat readings I got indicate at least that the cat is shot either way?

Sounds plausible to me that the new coil fixed the misfire.

If the cat is clogged to the point that performance is suffering, there are tests that you can perform to prove to yourself that the cat is the problem. One hack test I have done is to remove the pre cat oxygen sensor. You can plug the sensor back into the wiring and zip tie it up out of harms way. Then take a test drive. If the cat is clogged, the exhaust will escape out of the now empty O2 sensor hole. Performance will be better, but the exhaust will be obnoxiously loud.

You can also check the amount of backpressure pre cat - I watched a Scotty Kilmer video on that a while back, but have never done that myself.

Like you, I’d want to be certain the cat was bad before replacing it. I’m assuming the transmission is shifting normally and isn’t slipping?

I watched Scotty do it 2 ways. One he drilled small holes in the piping before/after the cat and used a kit that came with plugs. The kit he linked is no longer available. Then one where the plugged into the o2 sensor holes up and downstream. It looks like Harbor Freight has a kit that would work that way. Might go try and pick that up tomorrow.

I would like to do a compression test and though I’ve never actually done one, I “know” how. But then when I went reading up on the procedure to make sure I’m doing everything properly and carefully, I read about all the possible screw ups which could cause engine or computer damage if I go messing around with that. With the cat, it’s external and worst case scenario, I’ll be out $100 and a handful of hours and still have the problem.

Transmission… That was my big fear when I first started noticing this. My last 2 used vehicles both died of transmission failure but they gave no prior signs. I do feel the TB shift but only noticed it once I started scrutinizing everything. And then when riding in my wife’s '12 Forrester which runs great, I felt the same thing. The TB does do a lurch during the power loss issue. As I start to go up an incline, I’ll give a little gas to help it up but then it doesn’t feel like it reacts or react very much and slowly starts dropping in speed as I give more gas (a couple times I went to the floor with no initial reaction), then a lurch forward like all the sudden it woke up and got the gas I was giving. I know it could still be a tranny issue but there’s nothing I can do for that and all my research kept leading down the cat path due to the prior misfiring issue. I found a number of others have the same symptoms, also had prior misfiring and turned out to be the cat.

Another thing is that I’ve been testing it in cruise to see how it handles the inclines. Basically it handles them normally so far. I wouldn’t think anything was wrong going by how it acts in cruise. Are there known issues cruise can mask?

The issue with pulling the sensor and driving that way is that the issue only shows up on inclines that are a few miles away so I’d have to drive it loud that far. And it doesn’t always happen so if it didn’t happen that time, I wouldn’t know that it had anything to do with the sensor being out.

Basically the issue is intermittent, no code, no light and hasn’t been experienced in cruise, but with how it felt those times it happened, it seems like something must be wrong. So I have to weight the risks of attempting any diagnostics/repairs myself along vs the cost of taking it somewhere vs the possibility that I could drive this as a work car for a while without doing anything.

I’ve been researching and weighing my options all day and everyone’s replies have helped with that. But I’m not sure what I’ll do tomorrow. I’m leaning towards the back pressure kit and if the cat is bad, ordering one.

I think the harbor freight test kit is a good idea, if it’s cheap. You might get a shop to check the cat for fairly cheap, though. Then you can either confirm or rule out the cat as the problem.

The fact that it’s intermittent kind of leads me away from a plugged converter as a cause.

I personally wouldn’t worry about a compression test at 80k miles, especially if the engine runs normally at times.

The only thing I can think of that would cause the engine to run with adequate power under cruise control and low power without cruise would be the throttle position switch on the throttle pedal, assuming this 2005 is drive by wire and has no throttle cable. I don’t know how to test that theory, though. And I’d think a flaky pedal position sensor would set a code. Plus, since it’s an intermittent issue, it’s highly possible it just hasn’t acted up in cruise control yet.

One thing that hasn’t been considered is fuel delivery. The fuel pump could be weak and failing, not allowing enough fuel when demanded. Although, the truck should still downshift on inclines. I’m not clear if it’s downshifting when you press the accelerator going up the inclines when the problem occurs.

I hope I’m not muddying the waters. First step would be to check the cat since that was your original thought. The only time a plugged cat would cause an intermittent driveability issue is if the material inside has come loose and is rattling around inside - sometimes plugging the exhaust depending on how the material decides to lodge itself. Does the cat rattle if you bang the cat with your fist or a rubber mallet? If so, the material inside has broken loose and the cat needs replaced for certain.

Fuel deliver was also on my list of things, along with tranny, but when I found out the fuel filter is inside the tank, it wasn’t something I was going to be able to change. Basically, once I started finding people describing this the same way and having it be a bad cat, I went out and did the temp test and given my readings, I got tunnel vision focussed on the cat. Also because it was something I could most likely do for pretty cheap.

I’m honestly not sure if it’s downshifting on inclines. I’ve tried to pay attention but it all just feels so weird at that moment that I can’t tell. I can’t tell if the lurch I feel is the shifting or not. I’ll have to try and pay closer attention and see but I don’t recall it jerking or feeling a slip back before moving forward. It was like it just woke up all the sudden and jumped forward. The issue seems to not happen as much since I’ve started trying to pay attention so it’s been harder to get a good read on it.

One of the things I was going to try before I got focussed on the cat was change transmission fluid and look in the pan for metal pieces. Change the filter and maybe replace the solenoids. But then I found out there’s no plug on the tranny and I’d need to drop it while it’s full. I’ll definitely make a mess with that.

I pounded on the cat with my fist today and no rattle.

No, it’s not muddying the waters. I wanted to hear any other thoughts of what it could be or what to try. It gives me more to consider but that’s good. I appreciate the info.

Oh, one more thing. One of the first things that popped up when I searched on this symptom of going uphill were two people who had the intake hose collapsing as they accelerated and it was causing a power loss. The one poster only realized it was the problem for him when the other bought it up and he checked it out. They diagnosed it by disconnecting the intake hose. So I tried that and drove about halfway home from work one day like that. I felt an immediate difference. It sounded a little different and no loss at all going up any on the inclines. It felt very good going up them. Like I would expect it to. But like I said before, it doesn’t always happen. Still, it didn’t hesitate at all. But I got nervous driving like and pulled over to re-connect it. It also didn’t do it the rest of the way either but I felt like I could feel the difference vs having it off. When I got home, I had someone give it gas while I looked at the hose and it didn’t deform at all and is even hard for me to squash it at all by hand, so there’s no way it’s that. I also looked inside for any obstructions and there’s nothing. But it did feel like it had more stable power.

Then I thought about the filter since it would’ve been disconnected as well. I had checked it before and it looked totally clean. But I changed it anyway just because I had another, better quality one. It’s been happening less since and possibly hasn’t been so bad as the times I had to floor it but the issue isn’t gone and it happens so erratically that I doubt think I can really say whether it’s happen less or not. I’m going to keep a log this week driving to work and really pay attention to the behavior.

Well, I was pulling out of my garage to go to Harbor Freight when I had a close call with the edge of the garage door opening. So I get out to evaluate any damage and I hear this sound coming from the vehicle. Sounds kind of like a low intermittent belt or pulley squeal. But it’s not coming from under the hood. I trace it back to the rear and then I get underneath and trace it to inside the gas tank. It’s making it the whole time the car is idling.

I had been hearing a light squeal driving through the alley the last couple days but thought it was just my breaks squealing a little as I first pull out as I didn’t hear it after that. Until just now when I got out of the vehicle while it was running and parked halfway in/out the garage.

What can be gathered from this noise? Anything other than the pump failing?

I have a full tank of gas right now.

This thread should probably now focus on your fuel pump. Might want to configure a fuel pressure gage to see it while driving at speeds and monitor it when it starts acting up under load. Based on your temp readings on your cat, your cat is probably bad but may not be restricted.

Thread title changed.

Yeah, that’s what I was going to ask. If the temp reading could just mean the cat isn’t working properly but isn’t actually restricted. In that case, is there any concern driving it like that other than emissions (no inspections in my state)?

I’ll look into a fuel pressure gage. I went back out and with the car idling, I pounded on the tank with my fist where I could hear the sound and after about 5-10 seconds of pounding it reduced quite a bit and couldn’t be heard unless I was under the tank. I drove around, including a couple of the inclines that have been issues. No power losses but it did maybe feel like it was a little rougher overall than usual but that could just be that I was paying closer attention. Had the radio off and really listening. I work the next 3 days and will see how it seems in normal driving conditions. Oh, and when I got back to the garage and crawled under, I had to put my ear right up the the gas tank to hear anything. What I heard was a steady low volume but very high pitched sound (not a hiss). I don’t know if that’s a normal operating sound or not but it’s not something I’d ever hear if I wasn’t looking for it. I also poured 12oz of Techron cleaner into the tank. I have twice as much gas as it says it treats and I know it should be put in when the tank is low but I figured I might as well put it in.

A fuel pump has a motor and it’s normal to hear it when it runs. It should be a steady whirring noise, probably like what you heard when you had your ear to the tank. It is an on and off only pump so it should sound pretty much the same the whole time it’s running. If you have somebody turn the ignition from the off position to the run position (not crank position) and listen near the tank you should hear the pump turn on for 2 to 3 seconds. Then during cranking and while it’s running the pump should be continuously on with a steady humming noise.

What you describe is more like what it’s doing now. But before I pounded on it, the sound was too loud and squealy to be what it’s supposed to sound like and was rhythmic like it was turning on/off or trying trying do something. I seriously thought the belt was squealing before I realized where it was coming from. I had just checked the oil and thought I must’ve dripped some on the belt. So I guess for now I’ll see how it sounds and drives this week.

It drove totally fine to and from work. The sound still hasn’t returned at idle but I’m hearing a chirp/squeal/whine/whatever sound when I accelerate with the window down with something close to the driver’s side. Like going down the street. Each time I pass a parked car I can hear it. It also sounds pretty much like the birds and crickets so sometimes I’m not sure I actually hear it. But when I hear it cut in and out as I pass parked cars, I know that’s what it is. So I parked next to a store and could hear it when I gave gas.

So I’m jus going to continue to drive out this tank of gas and see if the problem returns. In the meantime, I’ll decide whether to tackle the replacement myself. I’m going to check prices a couple places but I have a feeling they aren’t going to be low enough to keep me from attempting it. I can get the ACDelco part for $250.

When this all started, I first thought of the fuel filter as a pretty easy first step. But I moved on when I read the tank has to be dropped. Then someone mentioned it’s a 3 person job, so I had no plans of doing it. But I just watched a video of a guy do it in his yard with a jack and it doesn’t look too hard.

Also, I’m thinking the fuel pressure test might not be of great use right now if it’s running totally fine. Though, that might not remain the case.

$250 is a lot of money for something that isn’t confirmed. It might be wiser to buy a fuel pressure gage to do some tests. There are things you can check with it without driving down the road with it. It’s almost always cheaper to have a good diagnosis before slapping on a bunch of parts.

True, but would a pressure test even confirm it, though? I’m thinking the test wouldn’t show an issue right now as it’s running fine even going uphill. Also, would the test showing low pressure really confirm the pump is bad or could it still be something else with the fuel delivery?

I think I jarred something when I was pounding on the tank that made a difference and maybe bought some time. It made the sound stop happening at idle and then it drove perfectly fine today. I was able to maintain speed over all the inclines with no funny stuff. I’m sure pounding on it didn’t fix it, and it might not last, but something definitely changed. If it wasn’t making this obviously not right sound, I’d just go on my way until a problem popped up. I’m thinking this sound is signaling a failure coming but that it might be able to pass tests at the moment.

I know it’s not confirmed but I’m pretty limited in the tests I could do myself (and that know I’ve done properly) and paying a garage to run tests is going to cost a fair amount. It might cost me $100 to find out I do need the $250 part that I’ll need to put in myself or pay a good bit more for someone else to do it. I’m weighting the risks and benefits. If I feel pretty good about it being the fuel pump, then I may decide to just chance it and hope I’m right instead of starting down the road of sinking money into diagnostics that may or may not even confirm a problem. Or confirm it’s the pump a couple hundred later.

I’m just more or less thinking out loud here and looking for others’ thoughts, so I haven’t decided anything yet. But I’ll definitely take your suggestion into consideration and I’ll look into whether I think I can put together the test, but right now with it running fine, I don’t want to pay someone else to do it.

Basically, though, the only problem at the moment is the noise and that noise is definitely coming from the fuel pump. If the power loss happens again, though, I’ll be making a decision quickly.