My wife drove my truck to work this morning and called and said the Check Engine light came on during her trip to work. I ran it to Autozone after she got home and got a free scan. The manager of the store ran a KOEO scan and the tool reported that a lean condition existed. No component was given. The truck idled fine, did not miss or drive poorly.

The truck (98 Mazda B4000 automatic) has 126k on the clock. I've done basic maintenance such as coolant flush, belt, spark plugs & wires, & air filter. No sensors have been replaced.

About 2-3 times for the past 2 summers, the temperature gauge will rise quickly causing the a/c to shut off. Then, I crank the heat on high and the temperature will lowers. Two minutes later, I'll turn the a/c back on with no ill effects. When this happens, the truck doesn't exhibit any driveability problems. I have no clue if this has anything to do with the problem because the CEL never came on before today. I thought that the thermostat was sticking closed. It's a cheap and easy fix.

I know that it's hard to diagnose a vehicle on a message board but I am looking for some folks that may have had the same sort of scan results and what fixed it.

Thanks,
Casey

 

On the lean code, seeing as how nothing more, or specific was found & with the mileage & vintage, of this ride, maybe a vacuum leak.

Perhaps something like a loose, cracked, split, or broken vacuum line.

Or maybe a acting out PCV valve, seeing as how you didn't say it has ever been replaced durng your scheduled maintenance.

Lower intake manafold gasket leak, from loose fastners is a common problem on the 4.0L.

Maybe a fuel delivey problem, but seeing as how you don't have any other codes, or driveability problems, that would point to that, perhaps we should just sit that one aside for now.

Just some thoughts for consideration.

 

I'll dig around and see if I can find a leak. I've got a can of carb cleaner that I can spray on some hoses to see if I can get a spike in idle speed. If I can see any of the lower intake bolts, I'll check them too.

I'll also check the PCV. That hasn't be replaced either.

Fuel delivery problem did cross my mind. It does have a reasonably new(15k-20k) fuel filter on it and I do run injector cleaner about twice a year through a tank of gas. It could always be an injector going bad.

When the CEL first came on, I initially thought it was O2's since they've never been replaced and my wife's Cobra (136k miles) had O2's that needed replacing. I dont want to throw parts at it, but at 126k, it might be good insurance anyway. They do appear to be in awkward locations though.

I did clear the computer memory by disconnecting the battery for 30 minutes so I will see how it acts tomorrow.

Thanks for the tips.
Casey

 

I think I'm becoming a psychic...

Cold Weather Related Issues Informational Thread

I have pretty much the same truck (98 B4000 auto) but I have a few more miles (137k). I got the lean codes last year in the fall, and it turned out in my case to be the Upper Intake Gaskets which were causing a vacuum leak. Cheap fix, but a little bit of a pain to take off the upper intake (a lot of things are connected to it). Other people have traced lean codes back to other vacuum leaks or fuel system problems.

-Jim

 

Thanks for the tip. I reset the computer last night and drove the truck to work this morning and the CEL did not return. If the truck can survive until the weekend, I'll check the condition of gaskets and hoses and will replace the PCV for good measure.

Damp and chilly mornings used to set off my Mustang's CEL. It would throw a MAF code. It was an aftermarket MAF and I ignored it since it would go away later in the afternoon.

Casey

 

My next prediction: your lean code and check engine light will return.

Right now, your truck probably has a P1000 ("OBD Systems Readiness Test Not Complete") code that says that the system has yet to run every test (at least since you reset it). Lean codes are also only tripped after two consecutive drives where the long term trim setting adjusts to the maximum (since the computer tries to compensate for the perceived lean condition with more fuel). Once you complete a drive cycle, the CEL and codes will most likely return, while your possible vacuum leak will be slowly getting bigger/your fuel pump possibly weaker, your gas mileage worse, and the weather colder (which means it is more of a pain to fix out in the cold). I hate to sound like a prophet of doom, but I ended up replacing my gaskets in a snowstorm. Maybe you're not concerned about that prospect in Alabama, but my hands are still cold from it.

You should really read some of the linked threads of the link I previously posted. They contain invaluable knowledge and answers as to how to diagnose exactly what your problem is.

Also, here is a site with more information on the Ford Drive Cycle.
Ford Motor Company Driving Cycle

-Jim

 

I don't know what the reciepe is for your "carb cleaner", but I'd be plenty careful with it, as many aren't friendly to plastics, or composits, (cause stress cracks or softening), rubber (cause it to soften or swell), paint & some aren't O2 sensor friendly either!!!!

As a suggestion for a more overall friendly "vacuum leak sniffer", why not consider rigging one, using a propane bottle, a length of tubing with a "sport inflation needle" inserted into the probe end of the tubing.
Just don't crank the thing wide open with too much pressure, it doesn't take much!!!!!

But be plenty careful, as both the propane, carb, or throttle body sprays, are highly flammable!!!!!

We don't want to hear in the news about some guy torching his ride, while sniffing out a vacuum leak!!!!!!

I've heard of folks using a length of hose to "listen" for the hiss a vacuum leak makes, but your problem, if it is a vacuum leak, doesn't sound like it may be bad enough to hear.

Just some thoughts to ponder.

Let us know what you find.

 

I agree with pawpaw on the dangers of flammable leak detectors. Be careful or you'll be .

While trying to find mine, I went to a dealership that my friend works at which has a smoke machine (it's inert, non-flammable "smoke" at 1psi or less injected into the vacuum system), which is the manufacturer recommended way of finding these leaks. We tried smoking the leak out, and when we didn't see it with that (had some trouble with the machine), we tried the carb cleaner method. I was fairly conservative, but my friend the mechanic quite liberally applied the carb cleaner to every vacuum line and around the intake. Luckily no fire, but we didn't notice any change in the idle either. I'll try to find it, but somewhere I found a number on the approximate size of a leak that could trip this code. It's pretty darn small, and from my experience leak detection isn't that easy.

-Jim

 

Oh I figure that it will. I just don't have time to fool with it til this weekend. I can drive my Mustang to work the next two days but I wanted to see how the truck was going to drive today since my wife was driving it when it happened.

Thanks for the concern. If the gaskets need replacing, I have a spacious two car garage that is pleasant in the fall and winter. In the summer, it is murder. I rebuilt the engine in my Mustang in that same garage two summers ago and it damn near killed me. Then again, I may not fool with it. There are a few shadetree mechanics in my area that I've used for some tasks I didn't want to handle.

I read several of the links and even found one from some guy that contained a detailed account of the removal of the lower intake. Believe me, I am not asking a question and letting others dig up all the answers for me. I've been digging around in the forums when time permits. I am a software engineer and I like to think I am methodical and use good judgement before I crack open the toolbox.

Also, I do appreciate the concern about the use of carb cleaner. In my experience, it would have to be a big gaping hole in a vacuum line for an idle increase to happen and you'd have to be deaf to not hear it. I'll inspect the hoses closely before anything is sprayed on them.

Thanks for all tips guys. After lunch, I'll read more into the intake gasket R&R.

Casey

 

While reading a few of the links, I saw that you had the same problem. Plenum gaskets are all you changed to fix it? I also noticed that you changed the PCV. Was it bad or did you replace it for general purpose?

Edit:
Well, I saw another thread where you said that plenum gaskets did fix your problem. So never mind....

Thanks,
Casey

 

Casey,

No problem, I apologize if I sounded soapboxy, often times people think the light is their problem and expect that resetting the computer and shutting the light off will fix everything. I see a lot of questions on this specific issue (especially in colder months), and some people have wasted a good amount of time and money on lean codes before by throwing parts/labor at it. I'm a bit-twiddler as well myself, so I agree that it's best to diagnose the root cause and fix that rather than just replacing parts.

Sounds like you've got a nice setup for fixing the ride. Unfortuanately, my truck won't fit in my garage. I do the same thing; when the truck is broken, take out the Mustang. Rockledge's writeup is a great read and has made many people's lives (including mine) much easier.

Good luck in finding the issue, and keep us updated.

-Jim

 

As I remember, I did the PCV valve more as a regular maintenance item since I had it on hand, just to see if it would have any effect. It didn't. Turned out to be the upper intake plenum gaskets, as you mentioned. Not saying that it's definitely your problem, but it seems to have been for several people. I also had a Ford mech from my buddy's dealership reccommend doing them. When I went to a dealer to see if I could get the gaskets that day, they didn't have them and told me they had replaced too many that week. So clearly it is a common point of failure. They are pretty much just rubber O-rings (not exactly an O shape) that sit into groves in the plenum and contact the lower intake on their edge. From handling them it's easy to see how a few years and many heat cycles could take a toll on them as well as how a lower temperature could cause them to contract and stop sealing as well (think Challenger).

-Jim

 

It appears that the plenum removal isn't too bad of a job. I'd probably rather do that 1st before attempting the lower for sure. I may attempt that in the next week or two.

DId you notice any erratic high temp readings when your truck was acting up?

No problem on the soapboxy stuff as you called it. By not knowing a person's level of mechanical competence with automobiles, you have to be that way. I've owned my Mustang for 16 years and have done just about all the maintenance on it since I have owned it. Clutches, brakes, head gaskets, cam, exhaust, axle seals, heater core/evaporator, engine rebuilds etc.... When it comes to my truck, I havent had to do anything to it and I am a bit gunshy about making major repairs to it.
I do appreciate all the tips.
Casey

 

It's not a bad one. Big things that got me were the brittleness of the EGR to DPFE hoses (new exhaust spec hose is expensive at the dealer) and things like that.

I didn't note any termperature issues. Biggest symptom (other than the light) was a noticable drop in gas mileage that got worse as time went on. After the fix, gas mileage returned to normal.

-Jim

 

They look like rubber bands. (plenum gaskets)

The replacements are MUCH thicker than the originals and a different color.. obvious a redesign.

I've done many of these... I can almost guarantee it's your problem.

Don't worry about the lowers. Good luck!