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Caver Dave
Dodge Dakota
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12/08/2004
20:11:16
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 Subject: 3.9 TBI DUMPING fuel, sputtering
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Hi, I'm so glad I found this forum, usually I work on antique radios....
My 1990 3.9 Dakota has had a intermittent miss for a while. This morning, damp, at 40 degrees it would stumble, misfire, and barely run at idle. On the way to work I get missing, a check engine light, and I read out trouble codes 41, 34, & 22. Based on the 22 I replaced the coolant temperature sensor and cleaned the EGR valve - nothing changed. Then with the air cleaner off I noticed that when the engine stumbles the TBI injectors are STREAMING fuel into the intake. The injectors are 6 months old. What else should I be looking at? Thanks!
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Caver Dave
Dodge Dakota
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12/08/2004
22:38:28
|  RE: 3.9 TBI DUMPING fuel, sputtering
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OK more info. While the engine was trying to run I unplugged the MAP sensor and there was no change! I was thinking the MAP sensor would affect the rich/lean ratio. Also the O2 sensor is probably the original 1990 part. Need some help guys!
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Just Looking
Dodge Dakota
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12/09/2004
01:37:32
| RE: 3.9 TBI DUMPING fuel, sputtering
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On my 2002 when i unplug the MAP sensor it will run extremely rich literlly blowing black out the exhaust.
Just make sure u unplugged the MAP and make sure it isnt from some type of vaccuum leak.
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vern
Dodge Dakota
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12/10/2004
13:41:16
| RE: 3.9 TBI DUMPING fuel, sputtering
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when you say streaming is it a full stream or would you call it misting?
it should be misting[faning it]if its not doing this you may have pluged injectors again or low fuel pressure
the miss could also be dist cap is cracked[allowing moisture in],coil,plugs and/or plug wires jumping fire,
i,d take a look at these also,neither the o2 or map should cause a miss.
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Caver Dave
Dodge Dakota
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12/11/2004
11:47:47
| RE: 3.9 TBI DUMPING fuel, sputtering
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Hi Vern, Saturday morning and it would barely run enough to pull it into the garage.
Misfiring is is the wrong word but that's what it felt like. When the engine runs normally I can see a faint spray of fuel and feel it on my finger. When it stumbles there is a MASSIVE squirt of fuel and it's actually flooding out momentarily. There's lots of smoke and smell of raw gas out the exhaust. I disconnected the battery yesteday to clear any codes and in running it 10 minutes this AM I have a code 41.
Now it's a constant problem but when it started it was so intermittent and instantly on/off I wondered if it was an electrical connector problem.
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vern
Dodge Dakota
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12/15/2004
09:02:19
| RE: 3.9 TBI DUMPING fuel, sputtering
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it,s possible its the map,the map converts the vaccuum to a electric impulse[volts/ohms]to the pcm,if the vacuumm drops off or the map is,nt working right it could give the pcm the wrong info causing the pcm to dump fuel,
low vaccuum-more fuel,high vaccuum less fuel
test the map or replace it.
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Bob Lincoln
Dodge Dakota
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12/15/2004
12:51:09
| RE: 3.9 TBI DUMPING fuel, sputtering
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code 41* Alternator field control circuit open or shorted
Maybe it's a charging problem such that the voltage reference in the MAP sensor is off. Have you checked your charging system? Should be 14-14.5 volts at idle, 12.4 or so volts off with battery fully charged.
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Caver Dave
Dodge Dakota
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12/16/2004
14:07:17
| RE: 3.9 TBI DUMPING fuel, sputtering
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Vern, I pulled the plug on the map sensor and reconnected it by jumpers. With the engine off, ignition on I measured 5V across the outer 2 wires, when I applied vacuum (sucked on a hose) the voltage on the center terminal decreased from ~4.5 to ~2 volts. This is the right type of response but I don't know if it's accurate.
Bob, my Haynes manual seems to show that the field coil of the alternator is directly controlled by the engine computer. I hadn't checked for shorts/opens yet but apparently it was running on the battery only. The volts got low enough that it wouldn't crank so I now own a battery charger. If I can't find a problem in the alternator wiring is the next step a new computer?
Sunday I put in a new oxygen sensor with no change. I plan to put in new, clean spark plugs and try again. Could a manifold belly pan leak cause low vacuum? I'm afraid I've got multiple problems and the truck's not worth spending a lot of money to fix them all.
As an experiment how about running the map sensor from an external 5V power supply with a common ground instead of going thru the engine computer? Also I would disconnect the alternator. Wouldn't that eliminate map sensor voltage issues and charging issues?
Dave
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vern
Dodge Dakota
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12/16/2004
20:41:55
| RE: 3.9 TBI DUMPING fuel, sputtering
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caver dave
THE 5 and 4.5 are good,but i don,t no about the 2
volts,sounds low to me with you just sucking on the hose.
the center terminal is your output to the pcm check pin-1 at pcm for same voltage,this will confirm if the wire is OK
your 90 don,t have a belly pan.
if you can take a vaccuum check if the truck will start,it should be 17-22in. at idle,steady needle,your hayes book should have a chart for vaccumm and given problems.
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wadak
GenIII
12/18/2004
19:29:36
| RE: 3.9 TBI DUMPING fuel, sputtering
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Caver Dave,
Just have to ask how many miles on your truck and when was the last time your O2 sensor was changed?
92 and 97 Daks both with many mods.
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Caver Dave
Dodge Dakota
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12/19/2004
22:05:41
|  RE: 3.9 TBI DUMPING fuel, sputtering
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wadak,
Uh, well, hmmm...(looking at feet)I bought the truck 4 years ago with 106K, it now has 276K and ran pretty good sooo....
This is TOO WEIRD.
New O2 sensor - no change
New spark plugs - no change
In heated garage 5 days to warm up, dry out- no change
Still had code 41 - OK so if there's a problem in the charging system we don't need no stinking charging system! Disconnected the alternator and it runs fine on battery! I measure infinite resistance across the field terminals. Took my "lifetime warranty" (it lived 9 months)alternator back to Autozone and got a new one. Seems to run fine now!
WEIRD - bad alternator = runs rich - WHOA!
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