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18:10:11 - 11/14/2024
V6 Dakotas
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gbofaz
Dodge Dakota
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7/11/2007
08:56:11
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 Subject: Emissions Failure
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Message:
I have a '94 Dakota 4x4 with 188K that failed emissions twice now for high HC's at idle only. Under load the HC's pass at about 60% of allowed, but at idle the HC's come in about double the allowed. After the first failure, I replace the plugs, wires, dist cap, rotor and air filter, but the second test failed about the same numbers as the first. Also, I replaced the O2 sensor about 10k miles ago and the fuel pump about 5k miles ago. I have been looking for vacuum leaks, and have found none. The EGR and PCV seem to be working fine. I have noticed the idle seems low around 600 and "hunts" between 600 and 900 or so, but don't know what the idle value would normally be. When at idle the timing mark is past the reference indicator, but would guess it is about 10 to 15 degrees before TDC when at idle. I also hear a ticking sound coming from the passenger front side of the engine, and after reading some posts I am wondering if it is the timing chain. It is deffinetly due for replacement, so I plan to do that, but could that also cause the emissions failure at idle or is there something else I should look at? Thanks for any advise.
Gary
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partsmanager
Dodge Dakota
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7/11/2007
11:04:22
|  RE: Emissions Failure
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Message:
Clean the Throttle-body out before putting any other parts into it. after 188k who knows whats growing in there. get a cpl cans of ccarb cleaner and a toothbrush and with the key off hold the throttle open, soak both side of the throttle plate then scrub with the toothbrush. keep extra rags handy to wipe off the brush.If you feel comfortable doing it take the Idle Air motor out and clean the port out too. this fixes alot of idle issues. Take your time and watch your fingers after doing this it may take a cpl cranks to start step on the gas pedal to get it running and clear it out after a min or so let it idle. let us know how you make out
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gbofaz
Dodge Dakota
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7/11/2007
23:39:58
|  RE: Emissions Failure
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Message:
Thanks for the reply partsmanager. I removed the thottle body tonight and clean it up with cleaner and it was definitely dirty with carbon build up. I also cleaned up the Idle Contoller tip as it had a lot of carbon build up on it as well. Unfortunately, when I put it all back together, I still have the unstable RPM's at idle and it was jumping any where from 500 to 1200 RPMs, and suspect this instability is related to the emissions failure at idle. I checked the throttle position sensor and had a voltage of 667mV while at idle and it was constant, even though the RPMs were all over the place. I did verify that the ticking sound I am hearing is coming from the injectors and not the timing chain, but a timing chain set replacement is still in the near future once I get the emissions problem solved. Not sure where to go from here. If anyone has any suggestion I would appreciate hearing them. Thanks.
Gary
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partsmanager
Dodge Dakota
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7/12/2007
11:21:17
| RE: Emissions Failure
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Message:
Now after cleaning the TBody I'd head for the EGR valve sounds like its leaking. spray some carb cleaner on it around the needle in the middle and see if the RPM's change as they age the needle burns away so even when its closed it doesn't seal esp true with 188k on the clock
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gbofaz
Dodge Dakota
JOIN HERE
7/13/2007
00:14:28
| RE: Emissions Failure
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Message:
Before I start with what things I tried tonight, I need to say that I realized while driving to work this morning that the unstable RPM I was seeing must be a ghost, because I was not hearing the RPM change only seeing it on my tach meter. I checked it further tonight and after rerouting the plug wire I was monitoring the RPM variability was gone. Suspect the wire was some how picking up stray charge from other wires or something it was routed next too. The extra charges caused current flow and the magnetic pick up of the tach meter to trigger and change the RPM value. I now have a stable RPM at 600. I still suspect my emissions problem exists, but can't prove it without having another test done. Anyway, I looked at several things tonight. I sprayed carb cleaner around the EGR valve, but no change in RPM. I had also used a vacuum pump to pull a vacuum on the EGR valve and verified that it held a vacuum. Will have to look into the stray voltage pick up issue later. I also validated the O2 is function, it varied from about 0.2 to 1.0 volts, once the engine warmed up. I plan to due a compression check tomorrow to look for any leaks or valves that are not closing. After that I will try and determine how much slop I have in the timing chain. After that I am out of ideas again. Again thanks for the suggestions.
Gary
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