Decrease in speed/MPH on an 01 QX4

[QX4dahuneys]

In the past 6-7mths or so I've noticed a huge decrease in speed on my truck. I've noticed when on the highway at 65mph, I see other cars zooming past by me, I have to hit 80-90mph to catch up to them. What causes the vehicle to decrease in speed? One thing I do want to point out is that I have not done an actual tune up on my truck, could that be the cause? What important parts should be replaced in a tune up to increase power on my truck again?

[Densetsu]

The speedometer being out isn't a power issue... power helps you get speed, but it doesn't play a role in measuring it.

Did you change your tires recently? If you put on smaller tires, the speedometer thinks one rotation of the tire gives 30" of travel when in fact it's only giving 25" (for an example). So when the speedometer thinks you're going 85MPH, you're actually only going 70MPH.

If it's not that, it could be the speed sensor or a bad instrument panel; are there any codes you can pull? Or people could just be speeding a lot on the highways.

Are you certain your speedometer is out? Can you use a GPS to compare speeds, or tell a friend to cruise at 65, then pace him and see what your speedometer says? You could also find some odometer calibration signs on the highway (one every mile) and make sure your odometer is right, would give more insight on the problem.
Modified by Densetsu at 10:42 AM 7/16/2009

[QX4dahuneys]

My speedo is working fine, I've made a comparison with my GPS versus my speedometer, both are marking the same MPH. As far as tires go, have not done any changes at all. Everything is pretty much the same. Now with the speed sensor, I don't know I would have to check that out.

[the converted]

I'm confused. Your going 65, you have verified that you are going 65 but people are passing you? I think that the pedal on the right will help you out, because 65 after all is a little slow around here.

If that's not what your trying to say, I'm sorry.

[UndeGuy]

My speedo is working fine, I've made a comparison with my GPS versus my speedometer, both are marking the same MPH. As far as tires go, have not done any changes at all. Everything is pretty much the same. Now with the speed sensor, I don't know I would have to check that out.

then it has nothing to do with the truck. traffic just moves fast, that's all.

I'm confused. Your going 65, you have verified that you are going 65 but people are passing you? I think that the pedal on the right will help you out, because 65 after all is a little slow around here.

If that's not what your trying to say, I'm sorry.

this TC is being goofy. I don't necessarily think 65 is slow. but just because the TC has to speed up o 75-80 to catch up to traffic doesn't really mean SQUAT. Unless this is a joke topic, the TC needs to really rethink what it is they're posting, cause at this rate, they're sounding... well, like an idiot.
Modified by UndeGuy at 3:07 PM 7/16/2009

[QX4dahuneys]

Ok, I'm getting answers that are a little off than what I expected. I don't consider my post to be some kind of joke either. Maybe I didn't make myself clear enough and I apologize.

My acceleration is not as powerful as it use to be when I first bought my vehicle 4yrs ago, I notice my truck tends to struggle to get to 65 when trying to fully accelerate. I feel like if I press down too hard on the accelerator I could blow a gasket or break something in the engine, yes I know this may sound silly but like I said not sure if this has to do with an engine tune up which is needed? I have not done a tuneup since I bought the truck at 58K miles, I currently have over 120K on it.

I've read in the past about vehicles tending to lose full throttle because of poor or no maintenance. Let me know if you can help or input something useful without any "smart" comments.

[the converted]

Yeah, sounds like it is time for a good tuneup. Plugs, filters, fuel injector cleaner, ect. You should notice a decent improvement in power. That reminds me that I have to do the same on mine.

[Densetsu]

Ah, gotcha now.

Air, fuel, spark. The big three for combustion. Air filter, spark plugs, and fuel filter would be the things I'd be looking at.

Air filter should be changed every couple years, spark plugs every 100k miles. If either is overdue for a change, now's the time to do it. The fuel filter doesn't really have a set replacement interval; it should just be changed whenever there's trouble getting power.

[KyooX4]

I would also recommend trying higher grade fuel. I always notice a difference in ease of acceleration between 87 and 93 grades. Perhaps some fuel additives?

[UndeGuy]

Ok, I'm getting answers that are a little off than what I expected. I don't consider my post to be some kind of joke either. Maybe I didn't make myself clear enough and I apologize.

My acceleration is not as powerful as it use to be when I first bought my vehicle 4yrs ago, I notice my truck tends to struggle to get to 65 when trying to fully accelerate. I feel like if I press down too hard on the accelerator I could blow a gasket or break something in the engine, yes I know this may sound silly but like I said not sure if this has to do with an engine tune up which is needed? I have not done a tuneup since I bought the truck at 58K miles, I currently have over 120K on it.

I've read in the past about vehicles tending to lose full throttle because of poor or no maintenance. Let me know if you can help or input something useful without any "smart" comments.

The problem is, that is NOT what you said in the original post.

In the past 6-7mths or so I've noticed a huge decrease in speed on my truck. I've noticed when on the highway at 65mph, I see other cars zooming past by me, I have to hit 80-90mph to catch up to them. What causes the vehicle to decrease in speed? One thing I do want to point out is that I have not done an actual tune up on my truck, could that be the cause? What important parts should be replaced in a tune up to increase power on my truck again?

The only comparison is your 65 vs their 75-80, which doesn't make any sense. IF you had said it felt like it was struggling, that would be a completely different matter. In fact, I wanted to assume that might've been what you meant, but if you've ever heard the phrase You know what they say about "assume," it makes an a** out of u and me.

And so, I cannot assume you meant something different, I can only respond based on what you said.

As everyone has already said, and in fact something you mentioned in the original post... tune up.

At the about 60k mark, there should've been a major tune-up, at 90k is another, then at 120k. In between, "every 15k" is a minor tune-up. According to one Nissan dealer, they even do every 7.5k. Depending on how you "pay attention" to your vehicle, you could probably get away with just the major tune-ups. In other words, even if there ARE other issues, you will get a MUCH different ride once you give it a tune-up.

Start from there, once it's done, see how it feels. If you're still struggling to get over 65, you might need to do other things. Sure, going from 87 to 93 grade gas could help, but not if its masking some other issue. Case in point, before I started driving the PF, my brother-in-law replaced half of the fuel injectors on the PF... was not cheap. I worry that I might have to replace the rest not too long from now. Have a mechanic you TRUST give it a look (after the tune-up), just to make sure there aren't other issues.

And yes, I'm also using 93 grade, but that was my decision when I started using the PF (based on experience with another car I used to drive).

***edited because of a stupid double negative.
Modified by UndeGuy at 11:52 AM 7/17/2009

[QX4dahuneys]

Thank you Unde Guy for your input in this...

As far as gas is concerned, I only use premium (93 or higher), I follow the instructions labeled on the gas cover.

[KyooX4]

Unde, lighten up a bit. Note that I said 'also', as 'in addition to (what everyone else has said)'. Higher grade fuel helps, but lack of it is most likely not the problem. Based on what the OP said, we know this is not the problem.

[UndeGuy]

Unde, lighten up a bit. Note that I said 'also', as 'in addition to (what everyone else has said)'. Higher grade fuel helps, but lack of it is most likely not the problem. Based on what the OP said, we know this is not the problem.

I didn't mean to imply anyone "shouldn't" be using higher grade, just that if you do, don't forget to keep an eye out for other things.

I admit, I've been guilty of taking possible answers and doing half a** jobs when trying to figure things out. Luckily for me, those times did not include the possibility of spend major $$$ and time.

Like I said, the reason I use higher fuel grade is because of a past experience with a Mitsubishi Mirage that I used to drive. It has a dinky engine and only 92 HP rating... but there is a noticeable feel when using 93 vs 87 octane gas in it. So, let me repeat, I wasn't saying the OP shouldn't use higher octane gas. ok?

[Empty V]

Thank you Unde Guy for your input in this...

As far as gas is concerned, I only use premium (93 or higher), I follow the instructions labeled on the gas cover.

I'll echo what was already said with the tune-up. My 01' QX4 was just crawling up hills and at first I thought it was my transmission giving out. It ended up being my fuel filter. It was so clogged that my engine was being starved, I'd change it ever 30K-40K miles. It's a bit of a PITA to get the hoses off but well worth the money saved. I'd have your MAF sensor cleaned as well.

Billy