# Check Engine Light as Engine Fully Warms



## Spokane95PU (Jan 14, 2017)

Am interested to know the first three places an experienced Nissan guy would investigate when CEL comes on after engine is fully warm? (Fully warm: 30-40 minute drive on a +75 degree day.) Truck is '95 V6, 4WD.

As engine gets fully warm when driving home on warm afternoon, CEL comes on, kicks computer into limp. Next morning, engine (and ambient) is cool, light is out, all is well for entire drive to work.

During much work under the hood this winter I replaced O2 sensor, fuel filter, PCV, serviced and checked output voltage of MAF, (EGR removed years ago), cleaned injectors. 

I'm guessing perhaps it's the MAF, or perhaps AIT (I think my truck has one), but am really not sure. Am hoping some knowledgeable folks at this forum can save me some headache with their recommended first go-to points.

Thanks very much!


----------



## jp2code (Jun 2, 2011)

Either you have a cheap O2 sensor or you have a leak in your intake somewhere in a vacuum hose or air intake.

You can spray a little bit of starter fluid in short bursts around the engine while it is running. Whenever you find a vacuum leak, the engine will suck up the starter fluid to burn and the engine RPM will change.

Pulling the codes would verify this is an O2 sensor or MAF error.


----------



## rogoman (Dec 16, 2004)

Spokane95PU said:


> Am interested to know the first three places an experienced Nissan guy would investigate when CEL comes on after engine is fully warm? (Fully warm: 30-40 minute drive on a +75 degree day.) Truck is '95 V6, 4WD.
> 
> As engine gets fully warm when driving home on warm afternoon, CEL comes on, kicks computer into limp. Next morning, engine (and ambient) is cool, light is out, all is well for entire drive to work.
> 
> ...


Your vehicle doesn't use an "Intake Air Temperature" sensor. Newer models 1996 and up however do; if a P0110 code is set, then the engine will go into "limp" mode. In your case, you might want to check the MAF and it's harness connectors. Perform an ECU code readout to see if any fault codes are set.


----------



## smj999smj (Jan 1, 2006)

Any experienced tech would check for the stored codes first. That would at least point to a direction. The engine control section of the factory service manual would have the diagnostic steps for the code(s).


----------



## Spokane95PU (Jan 14, 2017)

After fiddling with some other issues, finally got a chance to pull the code... 51: Injector Circuit. Now to figure out what could be going on with the injectors as the engine fully heats up. 
I had the injectors, supply line, and wiring all off this winter. A couple of them were pretty dirty, but I cleaned them all before reinstalling everything. Fuel filter is new. What changes as engine fully heats? Loose wiring fails? "Vapor lock" in fuel line? When the computer reports Injector Circuit, what is it really seeing? Am headed towards the manual.
Thx!


----------



## jp2code (Jun 2, 2011)

You are supposed to replace the little injector o-rings every time you pull injectors. Did you replace those things? I'm late leaving for work, so I can't post more.


----------



## Spokane95PU (Jan 14, 2017)

Yes, replaced O rings on all injectors. 
Engine seems to run fine on a cool morning. Takes me all the way to work (45 min) just fine. Problem shows up in heat of the afternoon; also after short run time then restart again soon, after engine briefly sits in its own heat, instead of cooling down for a few hours. (As in short run to convenience store. Problem shows at restart for return trip home.) Driving home from work when ambient is 75-80 degrees or more, runs fine for 15 min or so, then problems start. Usually stay with me all the way home.
Thx!


----------



## jp2code (Jun 2, 2011)

This is what I was looking for. If you did it already, then you are good.

I wasn't able to find it in the 1995 PDF manuals, so I looked back to the 1994 Service Manual PDF.


----------



## rogoman (Dec 16, 2004)

Spokane95PU said:


> After fiddling with some other issues, finally got a chance to pull the code... 51: Injector Circuit. Now to figure out what could be going on with the injectors as the engine fully heats up.
> I had the injectors, supply line, and wiring all off this winter. A couple of them were pretty dirty, but I cleaned them all before reinstalling everything. Fuel filter is new. What changes as engine fully heats? Loose wiring fails? "Vapor lock" in fuel line? When the computer reports Injector Circuit, what is it really seeing? Am headed towards the manual.Thx!


A code 51 is for the Injector circuit as you know. Basically what is going on is that the ECU is picking up a signal from the O2 sensor, that a particular "pulse" is either running rich or lean. Now, there can be several causes of this. First, the obvious. That's a leaking injector. To find if you do have a leaking injector, I would pick up a fuel pressure test kit. This will "T" into the fuel line just after the fuel filter. Turn the key on, then off, and watch the fuel pressure. It should hold between 30-50psi for quite some time. If it drops sooner than that, you probably have a injector sticking open. How do you tell which injector? Well, first you can try unplugging them one at a time. This will only eliminate a electrical fault with the injector.

Next, I would pull the plugs and inspect them one at a time. A plug that has raw fuel on it, is probably getting wetter than it should. There may also be carbon buildup on the plug from not burning off during combustion. At this time, its also good to make sure the rest of your ignition system is operating properly(plugs, wires, cap & rotor). Any problems with those may cause misfire, possibly creating your code. Now, there are other factors that may also cause this problem. Those could be the O2 sensor itself, MAF, vacuum leaks, the ECU and possibly something else, maybe even check the connecting plug at the injector harness (bad ground, etc).

Spraying components with a liquid mist to test for vacuum leaks is not very accurate. Use a vacuum gauge for good accuracy; most auto parts stores sell vacuum gauges. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source, usually somewhere on the intake manifold. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle body and at the MAF for cracks or loose clamps.


----------



## smj999smj (Jan 1, 2006)

I've had fuel injectors fail as they've become hot. I just had this issue on a Toyota 3.4L-V6 last week. Engine would start fine and after a half hour or more, it would start misfiring on #4 cylinder due to the fuel injector malfunctioning.


----------



## Spokane95PU (Jan 14, 2017)

SMJ99, Thanks very much! I appreciate the reference to engine operating temperature! Really has me wondering if that's my situation, too. How did you figure out which injector was the problematic one? Does the Toyota computer actually tell that?


----------



## smj999smj (Jan 1, 2006)

Well, it was a 99 Frontier, so it had OBD II. It had a cylinder 4 misfire code and after swapping the coil packs and spark plugs to different locations, the P0304 code reappeared, meaning it wasn't ignition related. Since it was intermittent, it would rule out a bad valve, meaning it was likely a fuel injector, or possibly a bad head gasket. With 200,000+ miles on it and nothing else that would suggest a failed head gasket, we decided to replace the set of fuel injectors. Resistance range of the #4 injector was also found to be higher than spec.


----------



## Spokane95PU (Jan 14, 2017)

SMJ, Thanks! Sounds like I need to go by auto shop to get a detailed code read. (Not sure they have the tools for my old '95. It's pre ODB technology.) While under the hood last night I discovered air leak. I suspect manifold bold. But, said bold is immediately adjacent to #1 injector. So dumb question: can injectors be source of air leak? Seems to me that if they're to leak, it will be fuel, not air, that leaks. But, am wondering if they can allow a vacuum leak as well. Any thoughts?
Also, any comment on use of rebuilt injectors?

Thx!


----------



## rogoman (Dec 16, 2004)

Spokane95PU said:


> SMJ, Thanks! Sounds like I need to go by auto shop to get a detailed code read. (Not sure they have the tools for my old '95. It's pre ODB technology.) While under the hood last night I discovered air leak. I suspect manifold bold. But, said bold is immediately adjacent to #1 injector. So dumb question: can injectors be source of air leak? Seems to me that if they're to leak, it will be fuel, not air, that leaks. But, am wondering if they can allow a vacuum leak as well. Any thoughts?
> Also, any comment on use of rebuilt injectors?Thx!


Fuel injectors cannot leak air unless the bottom O-ring is broken during installation however they certainly can leak fuel especially rebuilt units. Look at my previous post about testing for leaking injectors and testing for vacuum leaks. I would stay away from rebuilt injectors; a lot of them leak, have bad spray patterns and many are DOA.


----------



## smj999smj (Jan 1, 2006)

1995 would be OBD I. Code readers for these systems are pretty rare to find outside of older dealerships. The good news is you can read the codes using the red and green LED lights on the ECM, which is under the passenger seat. If it's a 2-mode system, it will have a toggle switch and if it's a 5-mode, it will have a mode screw to turn to get to the different modes. This site should help you:

Nissan ? OBD/OBD2 Trouble Codes


----------



## Spokane95PU (Jan 14, 2017)

Well, I took the air collector and injectors off in order to get access to the manifold bolts to torque them down and stop the above air leak. When I go the injectors out I found the real air leak: a torn injector cushion. It apparently got pinched, rolled, and torn when the injectors were last put in place. The cushion was torn clean through and also not really in it's seat. Replaced it, and another that was also poorly seated and put it all back together. Started it up and it ran great. 
Went inside, at dinner, came back out to the garage. Started it up and it ran terribly! Acting like I never fixed anything; bad "miss," as if in limp mode. CEL on and off. I think I may have discovered two loose plug wires (#3 and #6 ), but can't say for sure. In any, the wires don't snap on or fit snugly.
Engine seems to be acting like an electrical or timing issue.
Regular clicking with the RPM coming from the front of the engine, perhaps the distributor. Every 30-45-ish a louder click from the distributor area. The click sounds as if it could be an electrical arc. Opening the distributor reveals nothing abnormal.
Putting a timing light on it, #1 wire, it flashes as per normal operation, but then occasionally miss a flash, perhaps two.
Checking the ECU for codes, the red and green light come on but don't ever seem to start blinking. 
It makes sense that if the engine was sucking a lot of air, the distributor timing was adjusted to accommodated the maladjustment. And, now that it's not sucking the air any more, it needs to be readjusted. But, that doesn't answer for the clicking sounds and solid lights on the ECU. 
Any suggestions would be appreciated.
Thanks.


----------



## Spokane95PU (Jan 14, 2017)

1234567891


----------



## Spokane95PU (Jan 14, 2017)

*Solved! Injectors Failing as Engine Warms*



smj999smj said:


> I've had fuel injectors fail as they've become hot. I just had this issue on a Toyota 3.4L-V6 last week. Engine would start fine and after a half hour or more, it would start misfiring on #4 cylinder due to the fuel injector malfunctioning.


(Way past time to close loop on this topic!) smj999smj nailed it! Issue I was having was indeed injectors failing as they got warm/hot. Tough to trouble shoot as it's not very practical to pull off the side of the freeway and put your multi-meter on the injector circuits of a hot engine. After the tedious process of eliminating other variables, it came down to replacing injectors. Being on a tight budget I spent a lot of time pulling old ones out of old Nissans at the junk yard. I also learned the hard way not to count on more than 50% of the ones pulled from a yard as being salvage-able. I worked with a real good injector rebuilder (Mr. Injector .com ) who took the time to test each one electrically as it warmed up in his tester/cleaner. We ditched the ones that looked questionable and rebuilt the one's that looked strong. I put six rebuilt injectors back in and that fixed it! No more check engine, no more missing! 
BTW, I recommend Beck/Arnley rebuild kits with their "injector seat" ring, from RockAuto.


----------



## perfectlift-tips (Oct 17, 2017)

phew, this somehow resolves my issue with trouble reading the OBD/OBD2 Code thanks, man. you just save a lot of trouble for me.


----------

