Hey,
I've got a 2003 explorer 4.0 SOHC xlt 4wd automatic that has shown a cold start issue for way to long. When I start it cold the motor rpm flares momentarily. This only happens on the first start of the day. I've run the codes and only get a PO128, which is related to the thermostat not opening properly. I have replaced the thermostat and temp sensor ( the one that reports to the ECU) and there has been no change. I was thinking this may be temp related and after getting that code I was hoping the the new parts would eliminate the problem. No such luck.
I have noticed if I start the motor with the gas pedal floored for a few seconds, to defeat the fuel pumps, and then try to start it normally, it starts much better, no flare. So, cycling the motor without fuel seems to alleviate the problem. This seems like the type of issue that would set a code but doesn't. I really can't afford to take this into a shop so I'm looking for help troubleshooting this gremlin.
This motor has about 170K on it
Thanks

 

Do you have a scan tool that can datastream sensor values? If so, what is the IAT sensor reading as well as the ECT? Since trying to start in clear flood mode (stops providing injector pulse, not fuel pump) seems to enable the engine to start better, it sounds like you may be getting too much fuel during a cold start. Knowing what temperature the ECU really thinks the engine is at may help diagnose the issue.

-Rod

 

Hey Rod,
That's a good thought. I do have a scan tool but I'll have to check whether or not it will show sensor values. I'll check today
Thanks

 

To add to this scenario I've noticed recently that when I go to start the motor, first time, cold, if I cycle the key switch on (without actually starting) for a few seconds then off a few times that seems to eliminate the motor flare on start up. Not sure how that makes sense but for the last couple days this is how I start it and it starts what I call normally. No flare, rpms do rise somewhat but not excessively. This start up flare has always been momentary.
Rod,
My scan tool does data stream sensor values. So far I'm seeing coolant temps very similar to ambient temps. That seems normal to me. Typical morning temps are 35-40 degrees, sometimes dipping below freezing. That coolant temp sensor reads very close to ambient. I'm going to check again this morning while cycling the key switch if the sensor remains stable , continues showing the same temp .
Hope you still reading along,
Jcris

 

I guess I'm not really sure what you mean by "flare on start up." From you most recent post, it sounds like symptoms of low fuel pressure either due to a restriction in the fuel line or a weak/failing fuel pump.

If your scan tool can monitor the fuel rail pressure, that would be another good reading to monitor during the cold start attempts.

-Rod

 

Hello Rod,
Sorry for any confusion but I'm trying to describe what the motor sounds like on cold start. So rather than using the word flare to describe it, let me put it this way. What I mean is that the motor revs up beyond what I consider a normal rpm on cold start. I'm not sure that really helps. I realize on cold start there is an enrichment going on (open loop) that occurs for a short period of time , to establish a smooth idle. Open loop rpm is about 1050 (cold and in park). Once the motor warms up and goes into closed loop the idle rpm (in park) is about 840. When in gear (drive) the idle drops to 700. I got those numbers while using my scanner. My scanner monitors all kinds of parameters but I don't think it shows rail pressure. I'm not very familiar with it but it seems odd to me that it doesn't show rail pressure? Another thing that has been occurring is I hear the accessory belt tensioner rattling in closed loop while in gear (drive). Are these issues possibly related? Does 700 rpm seem to low? What can I do to correct this? Is there any way this could possibly be related to timing chain issues?
I hope you're still following along,
Thanks for your help
Jcris

 

Not all models have a fuel pressure sensor, so the scan tool not showing fuel rail pressure may not be a surprise. I was hoping to get lucky. You could always go the mechanical pressure gauge route. Your comment about the issue not happening if you cycle the key a time or two still has me thinking it's fuel pressure related. It might be running too lean on cold start due to low fuel pressure. Another thing to check for would be vacuum leaks. A vacuum leak would not be impacted by cycling the key, but might partially explain other idle issues.

I wouldn't consider 700 rpms to be too low. If anything, it might be a bit on the high side. This is where the vacuum leak might come in to play.

I don't expect that the tensioner rattle or the timing chain would have an impact on the cold start.

-Rod

 

Hello Rod,
Great info, much appreciated. I think I can rig up some sort of gauge for checking fuel pressure. Theres probably a Schrader valve somewhere to tie in a gauge? I'll have to check for vacuum leaks though, thats something I haven't done. Whats the best way to do that? With a running motor it's difficult to detect if using smoke not to mention getting to the areas. What areas would typically show vacuum leaks? I'm guessing around the (plastic) intake and any vacuum tubing? PVC valve? I've used propane to check for vacuum leaks on other motors but that always seems to risky, to me. I'm probably going to just replace the tensioner, belt and idler pulley just to see if that makes the rattle go away. Last time I did this was probably only 5000-10000 miles ago. And I used a shorter belt than called for.
Thanks again,
Jcris

 

Schrader valves on the fuel rail are kind of like fuel pressure sensors in that not all models/engines seem to have them. I've even come across some models where the factory service manual says there is a valve but when looking at the actual vehicle there is definitely no Schrader valve present.

I'm not sure there's an "easy" way to check for vacuum leaks. If you have access to a smoke machine that can insert smoke through the throttle body then you look for wisps under really good light, that's probably the safest. Otherwise the propane/aerosol spray method is certainly viable under careful supervision. My typical DIY method is to use throttle body cleaner in an aerosol can. Some people have used things like talcum powder with the idea that where there's a vacuum leak it will pull the powder in leaving kind of the negative of a carbon arc mark from and electrical spark. This also requires good light and the ability to actually get to the areas where a leak might occur. On you Explorer the upper intake manifold gasket, EGR valve, PCV valve, and any vacuum hoses are good candidates.

-Rod

 

Thanks Rod,
I'll try and make some progress on checking for vacuum leaks
Jcris

 

Hello Rod,
I was unable to find any vacuum leaks. I suppose that's a good thing. Cycling of the key continues to be a good work around. As you suggested earlier maybe this is a fuel issue. Maybe the fuel filter needs to be replaced? Perhaps even the "sock/filter" on the pump? A lot more difficult to get to that one though. There is a Schrader valve on the rail, course it's in a difficult spot. The key is a pressure reading when cold. How much pressure should there be? Should it vary cold to hot? Seems like it should be consistent and temp shouldn't matter, but I'm not sure.
Whats the possibility this could be clogged injectors?
Thanks again for following along,
Jcris

 

Key On, Engine Off (KOEO) and KOERunning pressure specification is the same value range - 60-65 psi at the rail. This value should not change based on engine or ambient temperature.

If this was a fuel injector issue I'd think you would notice an improvement in fuel economy and likely the engine would stutter at high engine speeds. If one or more injectors were not able to close, cycling the key before starting would not help out and the fuel pressure would bleed off pretty quickly (once you're able to measure the fuel pressure). If one or more injectors were partially plugged cycling the key could/would help with starting, but it would likely cause the engine to run a bit lean which would improve fuel economy but I would also expect the engine to stutter at high engine speed.

-Rod

 

Got parts today, new tensioner, idler pulley and accessory belt.
In the last couple days the tensioner has gotten much more noisy , just in the morning though, when cold. Before I ordered those parts I removed the belt to check all the pulleys. Each one spun free and looked undamaged in any way. The alignment looked good too, although I need to recheck with a straight edge. Not sure why the noise has increased so much recently, that does seem a bit odd. I don't think just removing the belt to check things over would have contributed to the noise but maybe it did?
Should be able to check fuel pressure at the rail today. Also going to do an oil/filter change today as well. Can't believe I've gone over 5000 miles since last change. Probably also pull the plugs to check and adjust gap.
Jcris

 

Installed new tensioner, idler pulley and belt yesterday. Right away the noise from the tensioner is gone, as expected with new parts. Specifically when I put the trans in drive or reverse, as the rpms drop to about 700 there is still no noise. That's a nice step forward and hopefully that will remain the same. Only time and miles will tell. I have to say the tensioner design has changed somewhat. Dayco has supposedly re-engineered the tensioner. That is something that I've noticed several suppliers saying about parts for older vehicles. I've always thought this was just marketing more than anything else but I'll see whether this design stands the test of time. For now the tensioner fix seems good.
As to the fuel pressure, I've not done that yet, hopefully today. I did order a new fuel filter cuz I don't recall having done that, ever. I did pull plugs (Autolite double platinum)and inspect, all of which were real close to proper gap at .054. I also have a new set of plug wires (8mm silicone) that I've yet to install. Probably not needed at this point but again not sure when they were last done.
The cycling of the ignition before start continues to alleviate the start up flare. I also pulled the PVC valve and cleaned it with some brake parts spray. Sounds better now. Thats a real crummy spot to get to that valve. Just noticed too that not only is the intake plenum all plastic so are the valve covers, Geez! Thanks to those still following along and I'll report what I get on fuel pressure as soon as I can get my lazy self to do that.
Regards,
Jcris

 

The plastic parts used in modern vehicles can be surprisingly resilient. For things like valve covers they tend to hold their shape better than flimsy old stamped metal covers. And because of that, they tend to seal better with the gaskets versus stamped metal units that easily warp during installation, removal, and/or cleaning.

My wife's 2014 Durango has a plastic oil pan and when I attempted to change the oil recently the drain plug was seized. After reading a few other posts of folks taking them to quick lube places to get the plug removed only to have the heads of the drain plug round off before breaking loose (or cracking the pan) I decided to get a bit rough. I used my cordless 1/2" drive Milwaukee impact that is supposed to be capable of something like 600 ft-lbs of torque and had to go full torque on that bolt before it finally broke free with no damage to the pan. The bolt was a bit misshapen from the impact action. I was surprised that plastic stood up to that.

-Rod