My Blog:Nissan Sentra hard to start when cold...

Hey guys, maybe someone here has an idea on what to look for next?

When it is 25-degrees F or lower out, our 2006 Nissan Sentra with a 1.8l and 83k miles is a PITA to get started. If you start it within 4-5 hours of it having already been up to temp it starts without issue. Only when it sits overnight is it a problem.

Basically when you crank it (it cranks perfectly fine, brand new battery) it sputters a bit. Do that enough and it gets warm enough and it will act like it actually wants to run, but you have to feather the throttle to kick the RPMs up far enough and then it will settle down and idle. When it is coming down from high revs it stumbles a little around 1800-1400 rpm and then drops into idle without a problem.

A little background, about 2 months ago it would start but the idle was erratic. Scanned it for codes and got a camshaft sensor error. Replaced the camshaft sensor (supposedly a common failure) and cleared the code and no more code, but every now and then the idle would do the same thing (basically upon startup rev to 1800-2000 rpm, start settling down to normal but stumble once or twice while getting there).

Now, here is what was done since it started flaking out:

- New spark plugs, OEM double platinum, gapped @ .044" factory spec
- MAF cleaned
- Throttlebody cleaned
- Throttle position set via procedure
- Throttle close position set via procedure
- Idle air set procedure run through
- Fuel pressure verified good
- Coolant levels are constant

Once it is running it runs great. No stumbles, no hesitations, no codes, great throttle response, etc...

I don't think it is a head gasket, since I have full heat and I haven't noticed a drop in coolant levels, with no smoking out the exhaust. Not to say it couldn't be a problem with the head gasket (another known issue on the 1.8l), but it has no usual "signs" of a head gasket failure. With the fuel pressure good, new plugs and no codes I am kinda at a loss. I don't have a jumper lead to test for spark because of the coil-on-plug design, but I can only assume it isn't a coil problem since it runs fine once it gets started (ie, the coils wouldn't get warm enough quick enough to recover from a bad internal connection).

If anyone has any other hints I would be more than interested in checking things out. It is a throttle-by-wire setup and I would have to assume that entire system is overly double and triple self-checking and would throw codes if it was a problem there. If the crank position sensor was at fault, shouldn't it throw a code?

I have done a ton of reading online and I hear of everything from O2 sensors (doesn't make sense on cold-start) being replaced to fuel pumps (fuel pressure checks out), to crank position and cam position sensors being replaced all the way to head gaskets/warped heads and the PCM itself being the problem... Sad part is that most of these are $600-1800+ solutions with most people being screwed by the dealerships (2-4 visits with them just throwing parts at it, which is complete BS).

Any and all help would be greatly appreciated.

sounds like maybe a sticky IAC?

Yeah, no IAC valve on this motor...

Everything is controlled by the throttle-by-wire system...

I have an electric block heater on the oil pan to see if that helps out...

I also have the FSM for the car, just a huuuuggge PITA to go through all the various diagnostics for damn near everything this thing needs to run... I am thinking of swapping out the crankshaft position sensor as well, since I did the camshaft I should have done the crankshaft at the same time...

welp, figured it out... was a bad crankcase position sensor...

but, it still won't start... won't even try now...

reason: the camshaft(s) are out of time with the crank... unplug the camshaft sensor and it starts right up...

So, anyone know how to retime the cam(s) without pulling the front of the motor off??? I heard they is supposed to be a "trick" to do it on this motor... Just can't find a proper reference to accomplish it.

well the cams dont just go out of time on a chain motor something else is fucked up.
or it has a bad ecm temp sensor its reading too hot to the ecm when your starting it causing the ecm to retard cam timing and lean it out.causing it not to start.

Timing chain is Prob. Stretched

There is a TSB for long crank time #05-052C it's something with the FPR on the fuel pump. If this isn't the problem then I would remove the valve cover and check for sludge. If sludge gets into the intake camshaft control solenoid you'll have issues. If the t chain was stretched it wouldn't run as good as he says or at all, plus it would make all sorts of noise. Nissan chains are pretty good unless one doesn't change their oil.

Also how did you reset your throttle body? Via scan tool?

I already reset the throttlebody using the factory procedure...

Oil was changed regularly and synthetic was used. When I pull the valve cover I will be setting the intake cam to the most advance position before resetting the timing.

Per a buddy who works on Nissans all the time it is a known issue with the 1.8l motors that they have headgasket and at times the cam(s) can jump a tooth. The chain on the crank is always where it should be (there is no way for it to be out on the crank the way it is designed), but they can jump a tooth on one or both cams. Rare, but it does happen I guess...

If the chain is stretched I guess I will be in for changing it. I will check the tensioner first... I am really hoping I notice that one or both cams are off a tooth. Would make for a simple fix considering you just have to pull the valve cover, the upper timing cover, use air pressure and set the intake cam to the most advanced position, insert an allen wrench to lock it into the most advanced position, ratchet back the tensioner slide and insert a pin to hold that and then adjust the chain on the cams as needed... undo that stuff and it should be a done deal...

If the tensioner is sticky or the chain worn I will have to assess what to do...

Once both camshaft and crankshaft sensors were replaced with good ones I noticed it wouldn't even try to fire... until you disconnected the cam sensor and then it fired right up with a cam sensor code... so the intake cam is definitely out of time with the crank at the very least...

Oh, and it has full fuel pressure in the rail prior to the fuel rails. Something like 55-58psi or somesuch at key-turn.

I already know the fuel pump has the infamous check-valve problem where pressure bleeds down upon shutdown. It isn't enough of an issue to swap out the pump yet, but if I figure out the timing issue and it runs good again I will most certainly have it on my list of maintenance items for next month. I found Bosch makes a nice drop-in replacement fuel unit including the level sender, regulator, check valve, etc... I just don't want to spend the cash on that right now without knowing what else I may have to spend money on to get it running... Hell I already have the rear seats out in case it was a fuel pump, so if it is a simple (and cheap) fix to get it running I will probably order hte Bosch unit right away and get that done before I put the seat bottom back in...

Not saying the chain couldn't have jumped but if the chain were to be stretched it would make a lot of noise when running. Is it noisy when running? Before you do a complete teardown can you inspect the cam to chain alignment marks with the valve cover off? Have you tested the intake cam solenoid, maybe its pulling timing not allowing it to start. Just trying to help with what your stating here.

Oh, don't get me wrong, I appreciate the input...

It doesn't make noise while running. It runs pretty smooth, thus I believe it is retarded more than advanced.

I will be checking out the cam advance mechanism when I have the valve cover off. I am getting over a sinus infection, thus with this cold snap I decided to wait a little.

I should be able to check the timing marks, cam hydraulic advance and all that stuff with just the valve cover off. I only need to pull the upper front cover to pin back the tensioner to try to get the cams in time. That is *IF* they are out, but I am certain they are...

There is a little lifter noise at idle, but nothing to be concerned about. Other than that it runs good... Under power it runs even and quiet. *shrug*

" There is a little lifter noise at idle, but nothing to be concerned about."

This is interesting because the engine isn't a hydraulic lifter design but a shim over bucket design. When the valve cover is off check the camshafts for scoring. Another possibility is a worn or leaking oil pump. Low oil psi could cause the what I call the VVTI intake cam gear not to work properly. Man there are so many different scenarios that could be the cause of the problem. Hopefully the noise you hear at idle isn't such but rather a noisy injector, some can be pretty loud. I've been wrenching for a while now and most issues with vehicles can be just an easy fix but often overlooked for the worse case scenario. GL.

Or how about the timing chain is wornout and hitting the timing cover

^ It would have to be pretty stretched out to be hitting the cover on this engine. Then at that point it wouldn't run as good as he has stated either.

Well, got the valve cover off today and inspected everything... Timing chain is fine, cams are fine, VVT actuates with air pressure without issues... Cams are in time... Tensionser is tight... no issues...

I swapped out the camshaft sensor again just in case the other one was bad. Nope, does the same thing... Car won't start with the camshaft sensor plugged in. Unplug it, starts right up.

I checked continuity of the grounds, no issues there.

How often do the PCMs on these things go out??? Is it something I can just purchase and put in, or does a dealer need to flash it for this car?

I will be going out and pulling every fuse and double checking again... but besides that is there anything left except for the PCM???

I pulled the battery for an hour, jsut to see if it would do anything different... As I suspected, nope... same business...

So, I started it with the camshaft sensor unplugged... then plugged it in right away... runs great, no codes... Took it for a drive, great power, good throttle response, no weird noises...

Drove it for a good half hour, all is good...

Stop back at home, park it, let it idle a little... perfect 700-750rpm idle... revs just fine, drops back to idle fine... no codes...

Shut the car off, let it sit for a minute, start it back up, same shite, no start, just cranks...

I then pop the hood, disconnect the camshaft sensor, start it, starts up, reconnect the camshaft sensor, got a code... camshaft sensor fault code... Clear it, doesn't come back (only came on because it was disconnected)...

So, can I assume the PCM is fooked? I mean I could just put in a relay that disconnects the cam signal while cranking the starter and reconnects it when the starter disengages. I will test it in the morning and if that works without setting a code, maybe I will just run it like that...

I really hate fucking hacking a solution to something that should not have failed... I have NEVER had a PCM go tits-up in any vehicles ever... Especially one that is running well with no "trauma" associated with anything...

I don't think I will ever buy another Nissan product based on this stupidity... I have never heard of Hondas or GMs or any other brand having this kind of ignorant problem... And it is pretty wide-spread per what I can tell online with a large number of people bitching about the same thing. Not saying that electronics can't go bad, but I would expect a car PCM to be more robust than that... I mean it can't be wiring since it runs great once you bypass the camshaft sensor and plug it back in...

Any input on any of this would be appreciated...

Weird, since you are able to do this how does the wiring look and are you getting the correct signals out of the cam sensor connected while first starting? It's either the sensor or in the wiring. I don't think it's internal engine parts it's something electrical for sure. Where did you buy the cam sensor from? You said you bought a good one buy OEM only IMO.

You will have to program a new ECU. You don't have to take it to a dealer but someplace with the proper scan tools. RK Motors on Holton Ave. has them. I've had a lot of faulty sensors, injectors, ECU and modules from auto part stores over the years. When it comes to these parts I will only recommend OEM parts. Just two weeks ago I got 2 bad spider injectors for a 4.3 GM from Napa. Installed the first one and got a Cyc #1 misfire, the next Cyc#5. The 3rd worked and they were the updated version. Per your FSM what does it say for a reading at the cam sensors connector from the ECU while unplugged?

Yeah, the sensors are from Orielly Auto... they look like the original ones, not the new metal can looking ones...

I know that autozone carries the OEM metal can ones, so I will stop there tomorrow and pickup one for the cam sensor. Obviously the crank sensor works since it runs with just that one plugged in...

If I pull the cam sensor out too far it will start but set a code. With it in all the way it won't start. What a huge PITA this stupidity is...

I have to lookup the P0340 code again and the diagnostics for it to go over the troubleshooting... I don't have a o-scope, so that kinda sucks, but I can do the other diags as a last resort.

It just seems like it isn't reading the cam properly. I did verify the cam end looks properly with the proper timing marks, just seems like the sensor can't read it, or isn't reading it properly consistently... I will also make sure there isn't something in one of the windows of the cam tomorrow that is screwing up the signals...

I will also go through all the grounds... already went through a few on the motor itself, but I will do all the body grounds too...