# BAD intermittent misfire....HELP!



## himilefrontier (Jan 21, 2003)

Well, I have a 1998 Frontier with a KA24DE/5speed and 261k miles on it. I have had a problem in the past where the engine would feel like it is running on 2 or 3 cylinders when it is damp out. It has always been the distributor cap when it started to do it, but this time it is not as I changed it with no difference. It does not do it at all until the engine warms up and then it will do it progressively worse as time goes on. I checked all 4 plug wires while it was doing it and all 4 were firing ( using an inductive timing light). I also listened to the injectors with a stethoscope to verify that all were opening and closing and they were. The fuel filter was changed 12k miles ago, so I doubt it is clogged, and the hose to the pressure regulator is undamaged. I wonder if the coil is going bad as it seems to be load sensitive, or maybe the fuel pump is failing. Either part is expensive and I am wondering how to know just what is wrong here. Could it be the crank angle sensor? I have a mild valve cover leak and I wonder if it is affecting it.( I will fix the leak tomorrow) Any suggestions would be greatly appreciated.


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## Oldnissanguy (Jan 6, 2005)

I assume you replaced the rotor when you replaced the cap. You might want to start by replacing the plug wires. They're fairly inexpensive, depending on what you buy, and it's a good thing to do anyway if you haven't changed them in a while. 

How many miles on your plugs? Are they showing any signs of fouling or abnormal deposits?

Just some things to check on the cheaper end.


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## azrocketman (Oct 5, 2005)

If it's a bad misfire you should be seeing a flashing "check engine" light; are you? If so, have you tried to read the code? I'm guessing a P030X (probably P0304). With your mileage I would not rule out an EGR system problem (clogged manifold ports, EGR valve).

Steve


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## frontera99 (Jul 3, 2005)

Judging from the miles on your fronty, it could be either of the two components.....

You could buy a coil at Autozone or an equivalent auto parts store and see if it resolves the misfire, if not, you could return it for a full refund.

This is the easier of the two, since the fuel pump is a PITA to replace. I hope it's the coil, LOL!


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## azrocketman (Oct 5, 2005)

frontera99 said:


> Judging from the miles on your fronty, it could be either of the two components.....
> 
> You could buy a coil at Autozone or an equivalent auto parts store and see if it resolves the misfire, if not, you could return it for a full refund.
> 
> This is the easier of the two, since the fuel pump is a PITA to replace. I hope it's the coil, LOL!


I'd disagree with you. If it's a true misfire the engine should be lighting the check engine lamp. Himile needs to follow through on the code to get an idea what system is at fault. Also (and I have experience here), EGR faults can cause engine misfires. I would not replace either the fuel pump or coil unless there is evidence (e.g. a fuel pressure check or scope the ignition system) of a fault.

Steve


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## himilefrontier (Jan 21, 2003)

It does flash the check engine light hen it happens, but it is intermittent, and gets worse when it has run for a while. It will sometimes run fine for 20-30 minutes, then act up. Unfortunately, the coil is not available separate and only comes in a $350 new distributor! I pulled a coil from a 1997 Altima today which looked identical to the one in my truck and will try it tomorrow as soon as I finish breaking in the cam in my Chevy 350 powered Cutlass. I want to have a backup to go to the parts store in case I mess things up. I also do not have a scan tool to read the codes, and the screw is broken off inside the ECU, so it rules that method out as well. I know I can just go to Autozone, but it's a PITA. If it were a clogged EGR system, I would think it would be constant and not come and go like it does. The plug wires are almost new and yes, I did do the rotor at the same time as the cap. However, either of those components would cause a steady misfire, not let the engine scream to the redline one minute and then cut to 2 cylinders the next.


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## azrocketman (Oct 5, 2005)

himilefrontier said:


> It does flash the check engine light hen it happens, but it is intermittent, and gets worse when it has run for a while. It will sometimes run fine for 20-30 minutes, then act up. Unfortunately, the coil is not available separate and only comes in a $350 new distributor! I pulled a coil from a 1997 Altima today which looked identical to the one in my truck and will try it tomorrow as soon as I finish breaking in the cam in my Chevy 350 powered Cutlass. I want to have a backup to go to the parts store in case I mess things up. I also do not have a scan tool to read the codes, and the screw is broken off inside the ECU, so it rules that method out as well. I know I can just go to Autozone, but it's a PITA. If it were a clogged EGR system, I would think it would be constant and not come and go like it does. The plug wires are almost new and yes, I did do the rotor at the same time as the cap. However, either of those components would cause a steady misfire, not let the engine scream to the redline one minute and then cut to 2 cylinders the next.


You need to check the OBD II stored codes and see what codes are being set. The EGR system can cause the problems you are referring to because its operation is inhibited on a cold engine. If you cannot read the codes and want to rule out the EGR system then I'd pull the valve (it's a pain at the back end of the manifold) and inspect. I'd also inspect the EGR ports as indicated in the following TSB: Service Bulletins Nissan Cars. I'm assuming that the '98 is the same as an '01 in this area. You may also be able to disable the EGR system by pulling a vacuum line and seeing if the misfire problem goes away but you may generate a new "check engine" fault. I am assuming that you have a Chiltons or a Haynes manual that gives basic troubleshooting advice for the components. One other thought, how old is the PCV valve? It's fairly cheap but a pain to replace.

Steve


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## himilefrontier (Jan 21, 2003)

azrocketman said:


> You need to check the OBD II stored codes and see what codes are being set. The EGR system can cause the problems you are referring to because its operation is inhibited on a cold engine. If you cannot read the codes and want to rule out the EGR system then I'd pull the valve (it's a pain at the back end of the manifold) and inspect. I'd also inspect the EGR ports as indicated in the following TSB: Service Bulletins Nissan Cars. I'm assuming that the '98 is the same as an '01 in this area. You may also be able to disable the EGR system by pulling a vacuum line and seeing if the misfire problem goes away but you may generate a new "check engine" fault. I am assuming that you have a Chiltons or a Haynes manual that gives basic troubleshooting advice for the components. One other thought, how old is the PCV valve? It's fairly cheap but a pain to replace.
> 
> Steve


The PCV valve has been replaced in the last year, and I also have a PDF file form of the FSM for a 01 Frontier, and most things are identical to mine.


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## Hank711 (Jun 19, 2007)

himilefrontier said:


> The PCV valve has been replaced in the last year, and I also have a PDF file form of the FSM for a 01 Frontier, and most things are identical to mine.


I am having a similar problem with my 2000, 2.4. If you disconnect the vacuum hose to the fuel pressure regulator, and plug it with a screw, you will increase the pressure under high manifold vacuum conditions. If this makes a change in the symptoms, then your problem is likely to be fuel related, not spark related. THis does not cost you anything to try, and worked for me- as a troubleshooting aid.


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