2007 vfr 800 vtec - cold start not working.

Interesting that it persisted even after a new wax unit, so i's obviously not that then. Adjusting the wax unit doesn't stop it happening either btw I tried that a month back and all it does it make it fast idle higher a bit longer (or shorter if you go the wrong way) It still bogs down after crank and builds up to the fast idle needing a bit of throttle to encourage it to get there.

Warmer weather is here now and the problem.....is gone.

I don't think it's battery related, I put a new battery in mine just before winter and I have a volt monitor on the dash and I bought a cold crank tester to keep an eye on it. I also changed my plugs to see if that'd help, no difference.

My fuel economy is absolute crap through winter which is no great surprise but I think the auto enrichment might be dicking around, I wonder if it's related to the air temp sensor...... meh. Forget about it till next winter again eh.

 

Recent Developments:

Out of disgust I have torn the bike down to the throttle bodies again. On the plus side, it seems to be starting 100% of the time now (I was having a hot restart issue). However, with the airbox off the low-idle speed on cold starts still persists.

I have tried starting with the air-temp sensor connected/disconnected and saw no difference in start-up behavior. My next attempt will be without the MAP sensor.

Also, this weekend I will borrow my father's manometer and try doing a starter valve sync.

He has a VFR (2003). I may try scavenging parts off of his known-good bike and trying them out on mine.

So now i'm down to a few things:

1) Electrical. Could it be the dreaded R/R and Harness issue? If so how would I root cause that? Also, it seems like the issue should be continuous. Not intermittent like it is. Also, why would cold weather affect a problem like this? Or could it be a bad coil? I'm not getting an EFI codes. I'd expect to throw a code if it was a coil issue.

2) Timing. When I pulled the Cams to check valve clearance did I put them back in off a tooth? Seems unlikely because I tripled checked. Also, other people who report this problem haven't touched their cams.

3) Tight valves. This could be a possible cause of the starting woes. But, I have checked the valve clearances and they were perfectly within spec 6K miles ago.

4) Could it be a bad injector?

It seems like, when I try to rationalize it, it has to be Air/Fuel related. This would explain why its worse in the cold (higher air density). Maybe I should pull the injectors and get them tested/cleaned. But, I don't know what could have caused a problem for my injectors...

 

Having the exact same issue in addition to the idle being very 'nervous'. It goes up and down constantly like if you just touch the throttle and then let go. So far I've ruled out (I have 2 spare throttle bodies):

SV Sync, Injectors, FPR, ECT Sensor, TP Sensor, IAC Sensor, MAP Sensor, replaced all vacuum hoses with new ones so no vacuum leak, New Battery, o2 sensors (tested with eliminators and without - no difference), TB Boots (no cracks / damage), replaced both CCTs with new ones

Not sure where else to go at this point. Could it be out of spec valves? I checked the front non-VTEC valves and they were all in spec. Plan to do the rear non-VTEC valves this or next weekend. VTEC works fine so I imagine there's not much point in checking those since they're not active in low RPMs?

As a temporary measure I've adjusted the fast idle wax unit through the nut on it (the one you're not supposed to adjust). It took considerable adjustment to get it to cold idle at 2k. But RPMs are still incredibly jumpy (up down up down constantly as if I was constantly touching the throttle and then letting go).

Anyone have any ideas what else I could check?

 

This morning I plugged in a known good MAP sensor, out of my father's VFR, and it did not fix the condition (no big surprise).

I also ran a healthy dose of fuel injector cleaner through the throttle bodies and then put in fresh gas. No difference.

I checked the headers BEFORE the bike hand a chance to stop being "lumpy". This means I let the bike run for 3-5 seconds while the idle was down around 800rpm. I checked each header and they were all approximately the same temperature (no dead cylinder).

So, i'm pretty much officially stumped. I still would like to try putting the airbox on and spraying ether around the throttle bodies to look for a vacuum leak. But, I don't expect anything to come of that investigation. At that point, I will just adjust the fast-idle wax unit nut and move on with my life.

What a frustrating dilemma.

 

Could you try and swap the ECUs and see if that does anything? I've literally swapped / tested everything else on mine that I can think of and I can't find the cause. I'm on the verge of giving up myself too, I already adjusted the fast idle wax unit on mine. Now when it starts it's at 1.5k and then goes up to 2k after a little bit. Had to do quite a bit of adjusting to get it to that point.

The only other issue I have is a small leak in the exhaust where the rear header pipe connects to the lower pipes. Getting that fixed next week but somehow I doubt that's causing this.

 

I looked at the exploded views on Partzilla: The '03 and '07 have different ECU numbers.

I'd hate to cause some failure of either of our ECUs because of incompatibilities.

I wondered about an exhaust leak. But I don't know how you could diagnosis this? I don't hear any noises that make me think "exhaust leak". But maybe i'm listening for the wrong thing

 

Yesterday I pulled the valve covers off my bike and checked valve clearance and timing. I didn't check the vtec valves. But all the "regular" valves were perfectly within spec, or maybe even towards the loose side. The timing was correct, which isn't a surprise but at least I can say definitively

After that I buttoned the bike back up, installed my new air filter, and gave it a test run. Of course it ran perfect. But, it was ~50 degrees when I started the bike. So this morning I tried again with temps around 40F. Again, the behavior was perfect. So, time will tell. I don't think I "changed" anything. But i'll see next winter how the bike behaves.

 

I've had the same issue with no fast idle, 08' w/8k. I discussed how the idle unit works on another thread. My conclusion is that when cold and the airbox off, the wax unit shaft SHOULD be contracted into the cylinder. You said you replaced the wax unit with no change. When your bike was cold and you had the airbox off, was the linkage engaged and the shaft retracted into the cylinder? Mine is stuck in the extended position. I'm either going to replace my unit or fab up a mechanical solution to engage the linkage like pre 02' vfr's.

 

It must be something along those lines, mine is starting like a champ now that ambient temps are above 10C. I adjusted the nut on my wax idle so that it was 'tighter' to force it to open but all it achieved was making it idle higher for longer which was ultimately counter productive since I was sat around waiting for ages for it to come down off fast idle.

 

My bike has been starting worse than ever lately. Sometimes it will come to life on the first crank (normal). Other times I will crank for 5 seconds and it wont start. Sometimes it takes 3 salvos of 5 seconds of cranking. Sometimes it takes turning the ignition off and back on. Throttle doesn't seem to worsen the condition or make it better. I do want to try cranking at WOT, which should clear out the cylinders in the case of me having a leaky injector.

I am suspicious of my PAIR system. Before I replaced the fast idle unit I could see a noticeable change in engine behavior at idle depending on if I covered the pair hose. When I checked the valve clearance when this issue first started, I replaced the O-rings for the rear PAIR openings (under the valve cover). I wonder if these o-ring weren't seated correctly or if I installed the wrong ones.

A symptom of this would be exhaust blow by (exhaust gas escaping past the PAIR o-rings into the head). I don't seem to having an issue with the case being pressurized. So this seems unlikely

Brian

 

Hi,been following this thread. I have a 07 rwb with 8000 miles. I'm getting the same symptoms. During cold starts it will fire up around 1000 rpm and slowly goes up to 1300 also running rich really bad fuel smell. I have a pc3, Leo Vince slip on and pair plugged. I'm going to open her up and see what I can find, like adjust the wax idle unit.... Etc. but I haven't heard anyone mentioned the fuel pressure regulator? Did anyone try to see if that's the culprit? I had a problem with the rc51 idling and bad fuel smell. Turns out to be the fpr. Fixed that and it idle like new, no more bad fuel smells.
Anyways. I've ordered another fpr for the vfr. I'll keep everyone posted.

 

watch out for chipmunk attack

 

FFS


Anyways i would replace the spark plugs, air filter, fuel filter and synch the starter valves before you start adjusting anything.

Sent from my A0001 using Tapatalk

 

Translated: is your airbox full of nuts/bedding for critters? Not uncommon for VFR's that have to hibernate for the winter.

A faulty FPR could also cause some of this but I would also expect the overall fuel consumption to be poor. They fail when the diaphragm gets a split which lets fuel leak down through the vacuum pipe into a cylinder inlet, but also allows the fuel pressure to be higher than it should leading to richer running.

Apparently hitting the wax unit linkage with some CRC can also work simple wonders for a stuck fast idle system.

 

First thing I checked for this morning. No rats or chipmonks. LOL..
Putting in new spark plugs and k&n filter. Just synced the TB.
Testing the fpr next......

 

When the FPR fails, you might end up with fuel in the vacuum hose; its worthwhile checking that immediately after running the bike to see if it has liquid in it.

 

I had a look at the fpr last year when mine was doing it, couldn't find anything wrong.

Mine is doing ti again now that the British weather is dropping below 5C overnight. I'd caked my linkages in WD40 last year to no avail. I was going to replace the fast idle unit but saw that others tried that with no success.

Stumped, tbh.

I'm going to remove my injectors to get cleaned during the worst of winter months to see if that does anything....

 

If the bike runs fine the rest of the time then your injectors are OK. The wax unit has to be the source of hard cold starting. I would take a look at it cold and then again when the bike is hot; you should be able to see a difference in the length of projection of the shaft. If there is no change when cold or hot then the unit is suspect. It maybe the same as a thermostat, (in fact mechanically they do a very similar thing) and they generally jam open in the hot position which would cause a cold start problem.

 

Is it possible to change the wax idle without pulling the throttle body? I know there's two screws on the underside that need to come out and disconnect the coolant lines but wonder if it's possible?

 

Sure, just take it to your local proctologist. Seriously I doubt that it is possible, but first you need to satisfy yourself that the wax unit ain't behaving anyway. It should be visibly obvious if the unit is extending and retracting as it should when hot or cold.