# 97 #4 misfire on just highway at first, now getting rougher



## somejerknamedbob (Jun 8, 2015)

Everything seemed fine with basic in town driving. Then engine would run rough on highway only as I got up to around 55 - 65 mph. I'd then notice some jerking/hesitation and sometimes the SES light would even flash. So pulled the code and got P0304. Checked the plug wires and sure enough #4 wire was in bad shape. So replaced all 4 plugs and wires. Not really a real big difference. I started to notice it really seemed to happen when I'd let up on the gas at those speeds and either coast or just reduce speed. So if I was consistent with acceleration it didn't seem to have problems but as soon as I'd let up then the hesitation would occur and sometimes even SES flash.

So this brings me to the fact that when I pulled the codes there was a P0402 that seemed to be in there for a while. So I also checked out the EGR valve and it seemed to be fine. As in I could plug the valve and the pressure would hold just fine. It seemed to move up and down cleanly etc. So I cleared the codes and only the P0304 comes back. The P0402 has never hit again in a good 500+ miles.

So I then figured I'd check out the MAF sensor. With a cold start the MAF voltage seemed kind of erratic. Bounced around 1.58-1.65 volts on idle. It was never a constant voltage. But it was responsive to RPM increase. So I tried unplugging it while the engine was running and it didn't seem to make much of a difference. I then plugged it back in and it killed the engine. So I took the MAF off just to be able to visually inspect it. Seemed clean. Didn't touch the probe or spray anything on it. Put MAF back on and now the truck seems to run more consistently rough than before. Even at lower highway type speeds.

Haven't had a chance to pull the codes on it to see if it's still only the 304 triggering the SES. Could all this be caused by a bad MAF sensor? Think the MAF is even bad? Could just that bad MAF cause only the #4 misfire?

Truck has 168k on it. MAF I pulled was Nissan and seemed to likely be original. I'm open to any wisdom anyone might have on it. It's driving me nuts and I know I can't drive it when the misfire is so bad the light gets to blinking. I appreciate any help.


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## somejerknamedbob (Jun 8, 2015)

Forgot to mention I visually inspected the cap and rotor and didn't see anything out of the ordinary. Even removed rotor and put it back on and was sure to make it good and tight.


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## jp2code (Jun 2, 2011)

If the parts are good, look for corrosion on the terminals or a wire making a short to ground.

Fusible links, too: Those cause odd behaviors.


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## rogoman (Dec 16, 2004)

somejerknamedbob said:


> Haven't had a chance to pull the codes on it to see if it's still only the 304 triggering the SES. Could all this be caused by a bad MAF sensor? Think the MAF is even bad? Could just that bad MAF cause only the #4 misfire?
> 
> Truck has 168k on it. MAF I pulled was Nissan and seemed to likely be original. I'm open to any wisdom anyone might have on it. It's driving me nuts and I know I can't drive it when the misfire is so bad the light gets to blinking. I appreciate any help.


It won't hurt to clean the MAF hot wire. Use only ELECTRICAL CONTACT CLEANER or a cleaner specifically made for MAF hot wire cleaning. This is the only thing you should use to clean your MAF. No windex, no carb cleaner, no brake cleaner, no rubbing alcohol, and no Q-Tips.


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## somejerknamedbob (Jun 8, 2015)

jp2code said:


> If the parts are good, look for corrosion on the terminals or a wire making a short to ground.
> 
> Fusible links, too: Those cause odd behaviors.


I didn't see any corrosion really on the terminals. Good call on fusible links and grounds. I'll look around cause it certainly can't hurt. The issues have fairly predictable timing so I don't suspect em too heavily...yet.


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## somejerknamedbob (Jun 8, 2015)

rogoman said:


> It won't hurt to clean the MAF hot wire. Use only ELECTRICAL CONTACT CLEANER or a cleaner specifically made for MAF hot wire cleaning. This is the only thing you should use to clean your MAF. No windex, no carb cleaner, no brake cleaner, no rubbing alcohol, and no Q-Tips.


Yeah I suppose I should just suck it up and go get some cleaner and give it a shot. I was hoping to have more definitive results on whether or not the MAF was straight up bad so I didn't end up buying the cleaner AND buying a whole new MAF. I'm just overly cheap I guess.


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## somejerknamedbob (Jun 8, 2015)

And by the way also checked resistance and voltage to fuel injector on #4 and it seemed to register fine on both. A friend is gonna try to come over later today and see if we can test the compression. I'm dreading the possible results. But I'll try to grab some MAF cleaner too and see if that improves anything. Thanks for your suggestions so far.


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## jp2code (Jun 2, 2011)

I'm going to go with Compression is OK.

Just my guess, though.


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## somejerknamedbob (Jun 8, 2015)

Sweet merciful jesus I sure hope you're right. I really don't have the knowledge, experience, time or patience to get in too deep on this truck.


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## rogoman (Dec 16, 2004)

Since the ignition seems to be OK, the #4 cylinder misfire could be caused by a malfunctioning fuel injector or it could be dirty. Run some good injection cleaner, like Techron or Redline SL-1, through the system; give the cleaner about a week or two to do it's job. Check this web site out for a possible electrical problem in the engine harness:

FIX: erratic idle, low speed driveability, possibly more - Infamous Nissan - Hardbody / Frontier Forums


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## somejerknamedbob (Jun 8, 2015)

It seems we think similar my friend. I ran 2 full tanks treated with injector cleaner through it and checked the voltage and resistance of the #4 injector to make sure it was even functioning. But I admit I did kind of cheap out on the injector cleaner and just used the generic O'Reilly's Auto brand. Might be worth another go. I also got some MAF cleaner and sprayed it down this morning and put it all back together but haven't had a chance to take it on the highway to see if same symptoms persist. I appreciate the link. I'll take a look and see what may match up.


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## smj999smj (Jan 1, 2006)

Spray carb cleaner around the intake gasket at the #4 intake runner while running to check for a possible intake gasket leak. If there's a leak, you'll notice a surge in RPM while you spray the carb cleaner in that area.


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## somejerknamedbob (Jun 8, 2015)

smj999smj said:


> Spray carb cleaner around the intake gasket at the #4 intake runner while running to check for a possible intake gasket leak. If there's a leak, you'll notice a surge in RPM while you spray the carb cleaner in that area.


This sounds promising. I'll give it a whirl. I very much appreciate the suggestion.

Quick update too. I cleaned the MAF and put it back together and ran it on the highway. I'd say there's definitely an improvement...unless it's just a strong placebo effect combined with massive amounts of wishful thinking. But I did still notice some of the same shaking/hesitation right around 60mph and 2400 rpm. But again it seems to occur when I let off the gas and coast for a second or three and then give it just a little bit of gas. That's when the jerking starts. But today it wasn't nearly as severe feeling and didn't trigger a flashing SES.

I'll do carb cleaner test and see what I find. Is it worth removing the EGR valve and seeing if that has a bunch of carbon buildup? I tested it with it still in place so don't really know if it's filthy up in there.


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## jp2code (Jun 2, 2011)

You are going to need a big wrench to get that EGR valve off. A 24mm or so, I believe.

Cleaning could never hurt.


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## somejerknamedbob (Jun 8, 2015)

smj999smj said:


> Spray carb cleaner around the intake gasket at the #4 intake runner while running to check for a possible intake gasket leak. If there's a leak, you'll notice a surge in RPM while you spray the carb cleaner in that area.


I tried spraying carb cleaner around #4 intake and noticed no difference at all. Even tried around general intake area and saw no change. So I guess that's good news.

I then decided to test MAF voltage again after cleaning it and it seemed fine. And that led me to notice that even while parked and revving the engine up to a very specific RPM it seems to cause the misfire. Right as it hits 1900 to 2300 RPM range it begins to shake and you can notice a definitive difference even in the exhaust pattern as it sort of sputters. I tried the white paper test and held an envelope up to the tail pipe to see if anything was coming out while it was running rough in that RPM range and paper came out clean. 

So anything BELOW or ABOVE 1900 - 2300 RPMs and everything seems to even out just fine. It's just there that the misfire seems to occur. Any ideas on what could cause something so specific?


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## jp2code (Jun 2, 2011)

Misfiring at that RPM means your truck is in "limp mode". Pull the codes to find out why.

You can't fix it by troubleshooting the issue, because the ECM is creating the problem so that you will get the engine repaired.


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