2.9 engine miss?

[Spitfire1975]

I have a 2.9 That overall runs very well. I have a problem where the engine will misfire(?), usually in 3rd or 4th gear while under heavy load (quick acceleration or towing). It will do it only once or twice, but consistently. Pulled codes and only getting a 31. Replaced EGR and EGR Position sensor and cleaned the Plenum real well. Replaced ALL gaskets. TPS is set correctly. IAC is good. O2 Sensor seems good. Still getting a 31 code. May have a bad connection in key ignition and have not completed a full tuneup (cap, wires, plugs, etc...). Fuel Pressure hangs right around 33 lbs. Fuel Filter was changed 5,000 miles ago. Can't find any vacuum leaks....Anybody have any ideas as to where I should go from here? Obviously I need to complete the tuneup......Thanks in advance...

 

[brommel]

Same issue here - 86 BII 5spd

Hi Spitfire-

I have the exact same code and issue as you. Heavy load misfire/stutter. I have replaced EGR, DPFE sensor, verified vacuum.. etc. It seems like I may have the same year BII as you as well. Just today I removed the vacuum line from the EGR and blocked it to rule it out as an issue. (No difference.) During engine speeds above 2500RPM the bronco runs well. anything below 2000 and it sounds like a big misfire and the engine feels unbalanced. One thing I know for sure is that my EGR AIR tube from EGR to exhaust manifold has some problems. I thought bypassing the EGR vacuum might makee differnce, but nope.

Let me know what else you have tried.

 

[brommel]

Brutally cold outside now!

I did a bunch of forum searching, and found others who had problems like this, but the problem posters never seem to post a resolution!?

The only thing that I have not replaced on my BII is the FPR, and I did not do that because I didn't see any failure (Gas in vacuum line..) I'm thinking of buying a vacuum gauge and testing it out, since it does feel like other engines I have had with vac. probs.

Someone out there must have the magic solution for this.

If not, I'll buy my third set of plugs and wires and see what that does.

:icon_surprised:

 

[Spitfire1975]

I have not had any real time to problem solve, but I can tell you that the FPR on my truck is relatively new. I am wondering if plugged cats or plugged (if even possible) charcoal canister could cause these issues. Seems common as all get out. My "miss" issues are all at 2500'ish rpm's. Idle is kinda rough. I was going to try and replace the computer (?) and see what that does as well. Keep in touch. Would be nice to solve this.

 

[Spitfire1975]

and by the way.....right now I am averaging just under 16 mpg's of mixed driving. Tune up will probably help this immensely....

 

[Kyler-]

I have a 90 bronco II and I have the same problem you guys do. It has a slight miss at idle and it idles rough. I tried a different computer right at the beginning and it ran exactly the same. I've changed the tps, the cts, cleaned my iac, checked my pcv, replaced the O2 sensor, changed the rotor, plugs and wires. Then it has been getting worse and worse where it bogs down. above 2000rpm it runs pretty good. so I checked my fuel pressure today and its right up at 45 psi.
Hopefully we can get this all figured out.

 

[adsm08]

O2

 

[Bronco_Chuck]

Ive been having the same problem with my 89. so far ive ruled out any problems with the spark or fule. i had a buddy run a vacume guage on it the other day and he said it ran about 15 at idle then at WOT it would drop to about 9 and as soon as the throtle was relised ti would jump up to around 17 or so. (not sure what the measurement scale on vacume is? IE. Psi, inches of H2O, or inches of mercury)

 

[heptofite]

i actually just recently posted a similar thread to this on rps.

my 86 4x4 auto b2 misses twice, never once, never three times, exactly twice, whenever i run it flat out, then it loses some power.

 

[brommel]

Anyone know what the vacuum reading should be at? Idle, WOT, etc.. I'm suspicious of vacuum because when driving, the first brake pedal push always sinks almost to the floor, and then the next push is firm again.. Seems like low vacuuum might cause that..

 

[shaysman]

have you cecked the timing when i rebuilt the engine in my ranger it done that and i went back and turned the dristubitor just a little and it hasnt done it again. make sure its in time before you start buying any more parts.

 

[Spitfire1975]

I am starting to think timing as well. Hopefully I can get that taken care of soon. Kinda busy with Christmas. I have also been wondering if maybe camshafts, etc... could cause this as they get older and worn down. Any ideas on how to best check O2 sensors? If I understand correctly the timing should be 8-10 degrees above 0 ?

 

[Bronco_Chuck]

i messed with my timing today and she runs like a raped ape now. you should check the O2 sensors with an ociliscope (i think thats how its spelled) as it has a signal that goes from 0 to .5 volts 0volts indicating a lean burn and .5 volts indicating a rich burn. if it was a cam shaft it would be a graduial decrease in power. and yes timing "should" be 8-10 degrees befor TDC but if your like me and dont have a timing light i would turn the distributor counter clockwise and the engine idle should even out and the RPM should increase slightly.

 

[slow29]

i have the same problem, but i know my solution my number 2 injector failed then i all i had to put in it was a 19lbs/hr from a 302, big mistake it gets fouled really quick, i set my timing at 12 degrees, advance the timing as much as you want until it starts pinging then bring it down, but 12 degrees is about the best.

 

[StreetRat]

Searching and searching. Finally an answer I can use! Thanks

 

[Spitfire1975]

Bronco Chuck - Think I can back probe somehow the O2 like I would the TPS?

 

[Bronco_Chuck]

yes you will need to back probe. and im sorry about earlyer the voltage schould change from 0 volts to about 1 volt. i would sugest using an ociliscope or a good multi meter that has a high and low memory. because the voltage will be changing to fast for most multi meters to display. the only other thing is make sure your engine is warmed up. and dont be surprised if you come out with readings like .2 volts and .7 volts thats pretty normal. and all tests should be while the engine is running.

 

[StreetRat]

'87 Ranger 2.9L auto 2wd

~I have gots to post this~

In a way, there are two filters. Inside the fuel accumilator is a wix#33268 filter. Clogged to the gills! Previous owner changed it before also. Teeth marks on it.
Blew my mind, I did not know that and never heard of it. As in, any other posts, its not even mentioned, nor in Haynes book. But one of the first filters at Advance On-Line and Napa. Guess more truck owers should be aware of this lil' nugget.
Well, the parts store closed for today.

Check into it... Hopefully this will help others!!!

 

[Spitfire1975]

and where exactly is this?? Excuse the stupidity on my behalf.....but where is the accumulator?

 

[HndMeDnBroncoII]

drivers side frame rail under the doormost guys dont bother with replacing the filter.
also double check all grounds they can wreak havoc in little annoying ways. and the eec relay-double check the plug and wiring. good luck