Dodge Repair/closed loop low rpm hesitation, missing at full throttle
QUESTION: 1995 Dodge Dakota, 5.2L V-8, 5-speed manual, 135,000 miles, Mopar performance computer,
Comp Cams roller rockers, stock ignition, Bosch Platinum 4 plugs, Jacobs ignition wiring, H&N
air filter, stock ram air intake, only engine work - new water pump at 80,000, runs strong
except for closed loop low rpm stumble. Mileage is down from 20 to 16 highway, and 17 to 13
in town with this problem. There are no symptoms when in open loop, engine still warming up.
I have an engine stumbling issue below 2200-2400 rpm when in closed loop and applying more
than gradual light throttle. Above this rpm there is no problem. When in open loop there are no
problems at any rpm when applying any throttle amount. I am suspecting the oxygen sensor but
I can't get it out even with a 1/2" breaker bar with a 16" cheater pipe on it. WD-40 hasn't helped.
The cast iron exhaust manifold was replaced when the truck was new with a set of Doug Thorley
headers so I am worried about stripping the threads in the mounting for it on the headers. Do
you think I am correct in thinking the oxygen sensor bad ? And do you have any help you might
offer me about getting the original oxygen sensor out without damaging the threads in the
bung for it ? I bought a couple of cans of freon freeze off for frozen bolts but haven't tried it. The
only thing remotely recent have been the Bosch plugs. This stumbling has been going on for the
past 3 or 4 years and I would really like to fix it. I do my own work for the last 35 years but
still need advice from time to time when I get stuck on something. Any help you can offer will
be very appreciated. Thank you for your time, Jim S.
ANSWER: Hi Jim,
Did you try for a fault code readout using the ignition key? Turn it on-off-on-off-on and leave on, doing that in 5 seconds or less elapsed time. Then watch the check engine light which remains 'on' to see it begin to flash, pause. flash, etc. Count the flashes before each pause. Then repeat for accuracy. Then let me know the results. You pair up the numbers in the order of appearance to get fault codes, the last such pair is always 55 which means end of readout. This access should be present in a '95 vehicle. A 21 code would indicate the oxygen sensor is at fault. Otherwise, let me know of another code number. Hold off on try to remove the sensor until we have any fault codes to consider.
Let me know what you find out.
Please read the PS below and respond.
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QUESTION: Hi Ronald,
It seems my use of special characters in my first send truncated the link to this answer or I would have been back
sooner. An email to the help line straightened me out on my mistake and I've found your reply. Thank you very
much for that. I did the codes check and it came up as usual, code 55 which is an all clear. I also have a Genisys
EVO updated to 2011 which also reads no code problems. It does occur to me that I am in open loop when
making these code checks, do you suppose that is a mistake ? I have been assuming the oxygen sensor is border
line or else just clogged up. I remember years ago when I installed the Mopar Doug Thorley headers I found the
oxygen sensor very dirty and cleaned it up gently with a medium stiff brush. By the way mileage new was 14 1/2
with mostly highway. The Mopar performance computer bumped that to 16, a free flow exhaust bumped it again
to 17 1/2, the headers brought that up to 19, with a H&N free flow air filter and the roller rockers and some
Splitfire plugs taking mileage all the way up to 20. That's a big improvement. Since I've never kept a vehicle for
less than 11 years and expected to have this truck for a long time the investment in the improvements seemed
wise, plus power went up at least 60 HP. As far as this stumbling miss at low rpm in closed loop with full throttle, I have read that some engines just don't like the Bosch Platinum plugs. I went to them a few years ago
because the Splitfire plug gaps would increase by one thousandth every thousand miles not to mention the
expense of changing them. The Splitfire plugs did make a difference in engine power and ran good, but
I just needed to keep pulling them to re gap or replace. The Bosch Platinum plugs last forever it seems but
this might be the problem ? What confuses me most is that when cold in open loop the engine runs so
perfect at all throttling usages. Plus it doesn't have this hesitation and stumble if I use full throttle when above
about 2200 to 2400 depending in which gear I am in, the higher gears requiring the higher rpm threshold,
when it is warmed up in closed loop. I have rebuilt two engines, a 1967 VW and a 1971 Datsun 240Z plus the
240Z's transmission 4 times, tons of brake jobs, water pumps, etc. so I have been a wrench jocky ever since
high school, 64 now, and I only get stuck on things rarely any more, but the new computerized cars seemed
determined to trip me up from time to time with me looking for help from one more expert than me. If you have
any ideas I would be grateful to hear them. Thank you so much for your prompt reply and the time you spent
to answer me. Thank you again, Jim S.
ANSWER: Hi Jim,
I am impressed with all your experience and knowledge. I too like to keep vehicles until they wear out! My two thoughts are:
first that one of the many sensors may be off-value but not so much as to set a fault code. Because of the onset in closed loop of the miss the sensors that only come into play in closed look would be the ones to check. With a plug-in diagnostic reader you might want to check the readings of those specific sensors to see whether one looks suspicious and change it out first.
The other item for an engine issue with no codes in my experience is the egr valve which may be gummed up and not closing tightly when it needs to (accelerating/idling). So try moving the stem of the valve back and forth (via the slot in the stem) to see if it is moving freely and closing tightly by its internal spring-action. WD-40 sprayed on the stem where it enters the valve body has proven to be effective when that is the issue.
I will be interested to learn if either of these ideas helps, and if not how you do correct it.
Thanks for doing a rating/nomination of me if you would care to do that.
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QUESTION: Hi Roland,
Intermittent problems are the hardest to fix. I might try going back to Splitfire plugs but my thinking is still the
oxygen sensor because of the drop in mileage only I can't get it out. In one blog the mechanic wrote that in a
fleet shop his only job is welding in new bung threads that the other mechanics have stripped trying to take
oxygen sensors out. The most common suggestion is to idle a cold engine for two minutes then try it but that
seems counter intuitive. I bought some Freeze Off that is supposed to shock bolts down to minus 40 in seconds
and crack the threads loose enough for the combined penetrating oil to get in but I can't find any accounts of
success using this approach. Most guys say just put more force on it but I've already been on it with a lot of
muscle and at least 24" of leverage. I've considered the same arrangement but applying an air hammer to
the rag wrapped padded end of the cheater pipe, an impact wrench won't fit but this might simulate it. So
far I just keep compensating with my driving habits and accepting the lower mileage. If you have any exposure
to getting stuck oxygen sensors out I'd love to hear them, they seem to be a common problem with no clear
cut answers to be found in any of the blogs. In my experience problems with leaking EGR valves cause problems
in all rpm ranges especially at idle, I'm sure a fault code would generate for this but I may look at changing it
out anyway if I ever get the oxygen sensor out and a new one doesn't fix this issue, only this oxygen sensor
may never come out, ha ! Thanks for trying to help people, Jim S.
Many thanks for that detailed report. The only observation I have would be that simply examining the egr valve and lubricating/moving back and forth the stem where it enters the valve body is nothing compared to removing the stuck oxygen sensor. So do give that a try. I do believe that if it sticks slightly ajar it will also come into play when you accelerate as that also requires the valve to be shut tightly.
I unfortunately have not faced the oxygen sensor remove so far so can't offer any suggestions to you.
Please let me know how it goes.
If you would care to click on the 'thank/rate' button below I would appreciate that.