Lurching at cruising speeds - two attempted fixes that didn't work. What's next?

[Springthing]

1999 Suburban. Bought not all too long ago with a few issues. This post has to do with one of the major ones.

When I drive at cruising speed, the 'burban lurches. When I start it up it's fine, when I'm under power it's fine, and when I have the foot off the gas pedal it's fine. The lurching/hesitation only happens when I want to cruise at a certain speed. If I press on the pedal enough to keep myself going 70 it feels as though the engine misses, causing it to feel like I'm towing a car dolly with a huge car on it - those that have hauled someone on the dolly will most like know what I'm talking about.

Because of another issue I was having with the suburban I tried two fixes.

The first was a new fuel filter. Cheap, easy, and step #1.

The second comes about because I have a twitching fuel gauges. The needle twitches/buzzes really fast and gives inaccurate readings at times. Because of this combined with the hesitation I changed out the fuel pump assembly and replaced it with a new one.

That didn't help either.

I actually broke down and went to the dealership and paid the $80 to have them diagnose the problem. Now, I don't mean any disrespect, but for the last few years of going to the dealership (or any garage) for a diagnostics I felt it's been more of a 'guess-nostic'. 95% of the time they being wrong as to what the problem is.

When it came back they told me, and please forgive me I'm doing this out of memory from the sheet that's sitting in the console in the suburban, they couuld only find that it could be two O2 sensors. Bank 151 and 152, if memory serves me correctly?

Does this ring a bell with anyone?

Dealership wants just under $400 to change out the two. I'm not trying to be cheap here but because of the sour taste in my mouth from the past few years and the thousands of dollars put into a vehicle that a certain dealership has YET to fix I'm not all about throwing $400 to fix something that is their 'best guess.'

I'm all about turning a wrench and getting my hands dirty, but any special skills/tools needed to do O2 sensors? Tough job?

Your comments and ideas are greatly appreciated and more than welcome.

Thanks!

[Springthing]

Totally apologize, forgot the information had been taken out of the signature.

7.4 vortec, automatic wiith 160k, single exhaust.

[MrShorty]

SES light comes on when it lurches? I'm guessing those are P0151 and P0152 codes that the dealership is referring to (which both referr to one O2 sensor not sure why they want to change both sensors if they are only getting a trouble code for one)?

If the SES light is coming on, then I'd start by pulling codes from the computer (sounds like the shop already did that, though I'm not sure that they've told you everything they found). Some places like Autozone can pull codes for you, though I wouldn't necessarily trust them to know what to do with the codes that are pulled.

If the SES light is not coming on, I'd pull codes and clear them, then drive it until it lurches to see if it triggers those same codes (maybe as pending codes) or different codes or no codes.

If you can gain access to a scanner, having it hooked up while driving to try to catch what is going on when it lurches might be useful.

I might also put a fuel pressure gauge on it and check fuel pressure to see if fuel delivery is contributing to the problem.

If it does really need O2 sensor(s), they usually aren't that hard to change, unless they are severely rusted to the exhaust pipe. Some good penetrating oil might be called for. They sell a special "O2 sensor socket" for taking them out, but I've always managed with just an open end wrench.

[Springthing]

Thanks for the information. Alldata shows that there are four of them in total and show the two that may need replacement. Doesn't look too difficult if the entire exhaust system is off the vehicle.... bah!

But I'll give it a whirl!

Thanks again,

[Springthing]

...nly find that it could be two O2 sensors. Bank 151 and 152, if memory serves me correctly?

Does this ring a bell with anyone?...

Actually it's 152 and 252...

AAaaaaand... in looking at the diagrams and information on alldata I think that's meant to read:

Bank 1S2 and 2S2 aka bank 1, sensor 2 and bank 2, sensor 2


I'll replace those two and will let y'all know what happens!

[Springthing]

Ok, so, the lurching continues!


I've replaced both rear (down from the cats) O2 sensors (those stated by the dealership diagnostic) and, back on the highway, the problem persists!

Going to go back to the dealership on Monday morning and have them give me another of these guesses. I'm hoping they don't guess that the hesitation is due to my needing a complete paintjob... at this rate, I wouldn't be surprised if they came out with that diagnosis with a straight face.

If anyone knows who the BOFH is.... I feel like I'm dealing with him, but in a mechanical sense.

I'll keep hammering away at it, wish me luck.

[MrShorty]

Ok, so, the lurching continues!


I've replaced both rear (down from the cats) O2 sensors (those stated by the dealership diagnostic) and, back on the highway, the problem persists!

Going to go back to the dealership on Monday morning and have them give me another of these guesses. I'm hoping they don't guess that the hesitation is due to my needing a complete paintjob... at this rate, I wouldn't be surprised if they came out with that diagnosis with a straight face.

If anyone knows who the BOFH is.... I feel like I'm dealing with him, but in a mechanical sense.

I'll keep hammering away at it, wish me luck.

Post cat O2 sensors are only there to test the catalyst efficiency -- they rarely have anything to do with driveability problems (unless the cats are clogged bad).

My code list shows P0151 and P0152 (assuming are the codes the shop pulled) refer to BanK 2 sensor 1. FYI, Bank 1 is the side of the engine with cylinder one in it, bank 2 is the other side. Sensor 1 is the one upstream of the cat and sensor is downstream of the cat. So if I've understood correctly, those codes point to a problem with the pre-cat sensor for the passenger's side cylinder bank. I feel kind of bad that you were led to believe it was the post-cat sensors.

A couple of things I might do:

1) Check for exhaust leaks. It is possible for an exhaust leak to introduce excess O2 into the exhaust stream which is seen by the O2 sensor.
2) If you can gain access to your own code reader (I've seen them at Harbor Freight for ~$50, if they still carry them). You might try a few things on your own. Clear the codes and see if the code comes back consistently. If it does, try switching the pre cat sensors from side to side, then see if the code follows the sensor. If the code follows the sensor, it is almost certainly a bad sensor. If the code doesn't follow the sensor, then you will need to look at other things (wiring or fuel problems or a vacuum leak or something).

[Springthing]

2) If you can gain access to your own code reader (I've seen them at Harbor Freight for ~$50, if they still carry them). You might try a few things on your own. Clear the codes and see if the code comes back consistently. If it does, try switching the pre cat sensors from side to side, then see if the code follows the sensor. If the code follows the sensor, it is almost certainly a bad sensor. If the code doesn't follow the sensor, then you will need to look at other things (wiring or fuel problems or a vacuum leak or something).

Again, I thank you so very much for your information. I think I can probably hit a HF Monday and will see if they have any readers. For the $50 each O2 sensor, I may just break down and give myself a full 4-way O2 sensor change. If that's not the problem, I'll know it won't be a problem in the near future!


Thank you so very much again. I'll you posted!

[95CTburb19]

if the dealer ship tells you your muffler bearing is bad, go to a new dealership