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Hi Everyone,
I have a 99 caravan with the 3.0L engine. I recently purchased a Solus scanner so I can work on my performance and driveability troubleshooting skills. (I’m not a professional technician, but took classes at CC for a while and held state certifications for a little while.)
Anyway, the Caravan is having issues with fuel economy. It’s getting about 17MPG driving on the highway. I hooked up the Solus and found that my Long Term Fuel Trim was sitting around 20%. I’m surprised I haven’t thrown a CEL yet. When I raise RPM to about 2000-2500RPM with the vehicle in Park, the fuel trim does not seem to have much of a correction. However, when driving the vehicle the trim seems to try and correct, reaching about 10-12%.
I originally thought I may have a vacuum leak, but haven’t been able to find one yet. I’m also thinking it’s time to do a tune up. However, I’m big on having data to backup the repairs I make, and hate to just throw parts. Are there any other checks I can do with the Solus to better narrow down the cause?
I am hoping to have some time on Monday to dig into it more, and I’m planning to pull a couple spark plugs and see what they look like.
Cheers
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Generally, when fuel trims are that high a positive number, there is a fuel delivery issue. Vacuum leaks can cause a rise in LTFT, but unless it is severe, won’t raise it that high. Have you checked the fuel pressure? You may be experiencing a weak fuel pressure regulator. If fuel pressure is ok, perhaps a dirty/bad injector is the culprit.
[quote=”cap269″ post=131052]Generally, when fuel trims are that high a positive number, there is a fuel delivery issue. Vacuum leaks can cause a rise in LTFT, but unless it is severe, won’t raise it that high. Have you checked the fuel pressure? You may be experiencing a weak fuel pressure regulator. If fuel pressure is ok, perhaps a dirty/bad injector is the culprit.[/quote]
I have not checked fuel pressure, and had certainly considered that possibility. Do you know off the top of your head of the caravan has a schrader style valve? I’m sure I can look it up. I don’t have a fuel pressure gauge so I would need to rent one.
Am I right in thinking that if it were vacuum related the LTFT should correct to more normal levels with higher RPM regardless whether the vehicle is in park or under way?
It has a schrader valve. EDIT: maybe… I just remembered that some years of this engine did not have a schrader valve and you have to use a T-fitting in the line. You should consult your service manual to be sure.
As the RPM increases, the vacuum decreases, so the leak ‘gets smaller’ and could even become invisible to the engine, at which case the fuel trims would normalize. This should be seen instantaneously in STFT. At deceleration the opposite happens.
If the fuel trims remain over 10% with close to zero engine vacuum, it is probably not a vacuum leak and instead a fuel delivery problem. In the case of a dirty/bad injector, the computer is increasing fuel trim so that the other injectors compensate. It usually won’t throw a code until it is unable to compensate.
[quote=”cap269″ post=131063]It has a schrader valve.
As the RPM increases, the vacuum decreases, so the leak ‘gets smaller’ and could even become invisible to the engine, at which case the fuel trims would normalize. This should be seen instantaneously in STFT. At deceleration the opposite happens.
If the fuel trims remain over 10% with close to zero engine vacuum, it is probably not a vacuum leak and instead a fuel delivery problem.[/quote]
Good deal, thx. As far as I remember from the troubleshooting I last did, LTFT stayed well above 10% while raising RPM and parked.
I’ll try and snag a fuel pressure gauge tomorrow and see what happens.
Regardless this thing probably needs plugs/wires/cap. We’re sitting at 152k, tune up parts last done at 107k back in 2008 I think it was. I just don’t want to throw tune up parts at it and hope for the best, I want the evidence, you know?
Also, I need to hone these skills, so it’s a good idea for me to go through the paces. Learn by doing, right?
[quote=”carsgovroom” post=131064] I want the evidence, you know? Also, I need to hone these skills, so it’s a good idea for me to go through the paces. Learn by doing, right?[/quote]
Exactly.btw, I edited my previous comment, please check it.
I agree with the above, first I’d check the fuel pressure and go from there. Let us know the results.
I’m still working on this, I just haven’t had a chance to get a fuel pressure test kit yet. Other projects are getting in the way at the moment. Hopefully soon. I will keep this thread updated as things change. I hate it when a thread just dies (especially when you come across it in a google search or something) so I want to see this through.
It looks like the caravan needs a special adapter to check fuel pressure. Tool 6539 fuel pressure adapter connects inline between the vehicle fuel line and the fuel rail. The autozone/etc rentable tools do not include that piece. I’ll either buy the adapter (around $50) or build one like his guy did with a fuel filter
Old thread I know, but I”m still working on this. Life got in the way and I’ve been really busy. I also thought the van would be gone by now, but that doesn’t seem to be the case.
Still no access to a fuel pressure tester. I’m working on that.
I was doing some other work to the van today (exhaust, alignment, etc) and decided to toss the solus on it. LTFT was still high around +16. STFT hovering around 0. upstream O2 was switching .09 to about .8. I pulled a plug off the intake and fed propane into it, and the O2 never really pegged rich (once when I stalled it too much propane). It seem to just continue switching. FT did seem to come down while doing that.
I’ve noticed when I go WOT it tends to kinda stink. I also noticed some sooty looking deposits along the exhaust I was working on today. Could that indicate it going pig rich on WOT?
I’m using this issue as a learning aid since drive-ability issues are a fairly new subject for me.
Reading through your thread I had a thought? Is this vehicle heavy? What I mean is do you drive around with a lot of weight in the vehicle? If so, this may account for some of the increased fuel consumption.
Outside of that, it would be nice to know those fuel PSI numbers just so we can either rule that out, or confirm you have an issue there.
Good luck and keep us posted on your progress when time permits.
[quote=”EricTheCarGuy” post=147573]Reading through your thread I had a thought? Is this vehicle heavy? What I mean is do you drive around with a lot of weight in the vehicle? If so, this may account for some of the increased fuel consumption.
Outside of that, it would be nice to know those fuel PSI numbers just so we can either rule that out, or confirm you have an issue there.
Good luck and keep us posted on your progress when time permits.[/quote]
Hey Eric,
Thanks for taking the time to reply to my thread.
The weight in the vehicle is fairly “normal”. I have a few things in it, but I also have the seats removed. I wouldn’t think there’s more than 100lb in the back of it. Some of my initial fuel consumption issue I think was related to significantly under-inflated tires (alloy wheels corroding and allowing air to leak).
This actually brings up a question though. Could weight, drag, towing, etc cause a change in fuel trim? Just curious, it’s something I’ve wondered about before.
As soon as I have fuel pressure data I’ll get it posted.
Cheers
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