Issues with Dodge GC

[beepbeep]

Hi,

I own (imported) FWD 2005 Dodge Grand Caravan 3.8 to drive kids and stuff around. I have recently run into some issues that made me scratch my head. I tried chrysler minivan forums but it the range of advice offered there was rather limited so I now try here.

Basically, it is throwing CE light with P0132 code = upstream O2 too rich. Guided by advices on Chrysler forums I replaced O2 sensor. Twice. Still have the error.

Finally I took out my WBO2 logger and fitted it to Exhaust and sure enough, it is running rich. Lambda 0.92 at idle and ~0.95 at speed. So Lambda is telling the truth. It is running rich.

I then measured TPS and it is working fine voltage follows throttle angle. Third step was to measure MAP: I took it out on the bench and it is reacting to vacuum changes: 4.65V on no vacuum, goes down when I suck on it.

But there is a twist.. When I fit it on the car it reports 1.2V at vacuum idle. Manually raising idle to 2000RPM makes it briefly go to 2V but then quickly goes to 1.0V (= lower than idle vacuum value??). To me it seems that there is a "flatspot" in MAP response curve. Is this plausible? Unplugging MAP makes idle lambda regulation go to 1.0 (as it should) but it also makes car undriveable.

I hate throwing parts at problems so my first step is to order new MAP (quite cheap) and take it from there. If it doesn't help I guess next step would be to measure fuel pressure? FPR is apparently "built into" fuel filter and in really awkward space, so I would rather not do it if I do not need to.


Any input is appreciated.

[porsche tech]

Not sure what all the specs indicate but was trying to think of most obvious things to make it run rich. Have you checked temp sensor(s) operation? Maybe the engine thinks it's cold when it's not. Just a thought...could be out in left field. I remember with Porsche, often times the O2 faults were triggered by something else.

[beepbeep]

Hmm, true. Tech sensor reporting too low will make it run rich but in that case, it should not show CE as it would be stuck in perpetual "cold start enrichment". Anyway, that is a good hint. I will ohm temp sensor as well!

[wilnj]

Originally Posted by beepbeep

Hmm, true. Tech sensor reporting too low will make it run rich but in that case, it should not show CE as it would be stuck in perpetual "cold start enrichment". Anyway, that is a good hint. I will ohm temp sensor as well!

I have that going on with my Jeep Grand Cherokee. Temp sensor reading too low for too long will trigger the CE light.


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[beepbeep]

Hmm,the plot thickens. I have purchased OBD2 scanner and observed live values. Weird MAP behaviour is only present in neutral. In drive, MAP corresponds to vacuum values the way I expect them to. So I suppose MAP is fine too. Coolant temp reported by OBD2 is correct as well. After car warmed up and I cleared the codes, everything is fine. Short term lambda adaptation is quite large though: at low load it can reach -10% and at high loads +5%.

These cars are incredibly cheaply built. Tiny brakes on 2.5 ton vehicle, plastic (!) brake caliper pistons, leaf springs in the rear, no interior air filter fitted, FPR and fuel filter built in one unit (not even compensated for manifold pressure) that lives on the fuel tank. My working theory right now is that FPR/filter is clogged and providing too high fuel pressure, leading to intermittent rich condition.

I loaded it with injector cleaner, next step is replacing filter

[fanaudical]

Leaking or worn injector that won't fully close?

[beepbeep]

Originally Posted by fanaudical

Leaking or worn injector that won't fully close?

Perhaps, but it would leak all the time and not just sometimes. Also, it would lead to very messy running (uneven AFR across cylinders). If I disconnect MAP, ECU is able to compensate and AFR goes bang on to 1.0, so it is probably not injector.

My bet right now is fluctuating fuel pressure. Fuel return/filter might be clogged so fuel pressure briefly goes above what can be compensated by computer and it registers error code.

I have new FPR/filter assy but it is placed in the most awkward place possible: under the car, on the top of fuel tank.

[asphaltgambler]

Also verify actual engine temp vs scan tool reading if you have a temp 'gun's to aim at the outlet of top radiator hose . Those are speed density systems ( no MAF ) so temp readings from coolant and inlet air with MAP needs to be right on money. If not typically the ECM firmware will 'fail' to slightly rich and you won't see it until the primary O2 sees it past the window.

[beepbeep]

Originally Posted by asphaltgambler

Also verify actual engine temp vs scan tool reading if you have a temp 'gun's to aim at the outlet of top radiator hose . Those are speed density systems ( no MAF ) so temp readings from coolant and inlet air with MAP needs to be right on money. If not typically the ECM firmware will 'fail' to slightly rich and you won't see it until the primary O2 sees it past the window.

Thanks. Yes, it is speed/density EFI. No AMM present. IAT is plausible (5 deg higher than ambient) and coolant temp is on the money (90-100 deg C). Fuel pressure is not compensated for intake manifold pressure though. Compensation is done in ECU instead.

Fluctuating short term fuel trim is smoking gun that something is fishy with fuel pressure. I will try to find a nipple on fuel rail and measure pressure.

[rattlsnak]

MAP sensors were notoriously bad in those years and I cant remember the cutoff year on when they changed the setup, but some fit right into the intake manifold and some had a vacuum line running to the nipple, and when the sensor would start to go bad, the vacuum would suck a gel like particle that partially clogged the line causing all sorts of issues like that.

[Shifter]

Take a look at your fuel trims, that will give you a better idea. I suspect your long term fuel trim will be high, which will give you a rich O2 sensor reading.

[HardDrive]

I must ask, why would you import this vehicle?

[beepbeep]

Originally Posted by Shifter

Take a look at your fuel trims, that will give you a better idea. I suspect your long term fuel trim will be high, which will give you a rich O2 sensor reading.

Thanks for the input.

Indeed, my long term fuel trim is dithering around -7%. I assume that once it goes beyond certain value (-10%?), ECU says "fcuk it, something is wrong" and flips the CE light?

Short term fuel trim is all over the place...-9% on low load, +4% on full throttle.

[beepbeep]

Originally Posted by HardDrive

I must ask, why would you import this vehicle?

Haha, good question. I bought it from a guy nearby who imported it from US for reasons unknown. (we also have naturalized EU version called "Chrysler Voyager", basically the same thing with bigger brakes and another name). I bought it as much cheaper and roomier alternative to Volvo XC90 and use it to haul kids and stuff around when we need extra space. Kids love it. It is really cheaply built but somewhat "exotic".overhere. You do not see many rolling around.

[Bob Kontak]

Originally Posted by beepbeep

Indeed, my long term fuel trim is dithering around -7%. I assume that once it goes beyond certain value (-10%?), ECU says "fcuk it, something is wrong" and flips the CE light?

Short term fuel trim is all over the place...-9% on low load, +4% on full throttle.

Negative fuel trim is telling you the car is adding less fuel because it is already too rich.

Is there a schrader test port on the rail? Check if your fuel pressure is holding.

I think this is a mechanical issue like a jacked injector pissing unwanted fuel in.

[porsche tech]

Another thought I had about a rich condition: Porsche had a fairly regular problem with a bad diaphragm in the fuel pressure regulator (especially 944 and 924S) and unmetered fuel was being sucked in through there. If you pull the vacuum line off the regulator sometimes you would see or smell gas there. Given the intermittent condition not sure if that would apply...just a thought.

[beepbeep]

Thanks for all good input! I will do one last try to change to OEM Denso O2 sensor and see if it works. Apparently, these cars are very picky about O2 sensors and first two I fitted were 1. wrong part # 2. Right part # but some Chinese junk brand.

What makes me think it is O2 is that it is stuck at 1.25V while downstream O2 is cycling as it should. Also, O2 output is typically between 0.1V and 0.9V.

bad diaphragm in the fuel pressure regulator

These cars are unbelievably cheaply built. There is no FPR on the engine, FPR is plastic part mounted on a tank and there is no vacuum line at all...it is returnless system with constant fuel pressure regardless of intake vacuum. I suppose they let ECU map handle different pressure delta over the injector instead.

Is there a schrader test port on the rail? Check if your fuel pressure is holding.

There was a until 2002, then Chrysler removed it to save money. So you need a T-port adapter in order to measure pressure.

P.S.
I really like the utility but am confused on just how cheaply built this thing is. Leaf springs in the rear, no cabin air filter at all, no fuel filter, undersized brakes from Chrysler K-car, plastic (!) brake pistons, no AMM (just MAP sensor), no fuel filter, no vacuum compensation for fuel pressure. They really went all the way with "decontenting"...

[Bob Kontak]

Originally Posted by beepbeep

I really like the utility but am confused on just how cheaply built this thing is. Leaf springs in the rear, no cabin air filter at all, no fuel filter, undersized brakes from Chrysler K-car, plastic (!) brake pistons, no AMM (just MAP sensor), no fuel filter, no vacuum compensation for fuel pressure. They really went all the way with "decontenting"...

I owned two in the 90's. They were famous for transmission failure.

[pavulon]

As an aside and because I think their utility is undeniable, did these vehicles' build quality ever improve?

[beepbeep]

Update: I got it working! It only took fitting OEM Denso O2 sensor...it seems that is is only happy with Denso and nothing else

Now the AC lines going back seem to be leaking due to corrosion


P.S.
It also summarizes my Ebay experience: Chinese knockoff O2 costs 30$...I ordered three different ones and none worked right.

Finally, I bit the bullet and ordered OEM Denso from Ebay Chrysler parts dealer (cost me 90$ here in EU). And he sends me Chinese knockoff again!! When I complained they did the usual "sorry, somebody packed wrong. You can get 15$ refund". After some more mailing they agreed to send OEM for free and bingo, everything works.