Jump to content


Welcome to Ultimate Subaru Message Board, my lurker friend!

Welcome to Ultimate Subaru Message Board, an unparalleled Subaru community full of the greatest Subaru gurus and modders on the planet! We offer technical information and discussion about all things Subaru, the best and most popular all wheel drive vehicles ever created.

We offer all this information for free to everyone, even lurkers like you! All we ask in return is that you sign up and give back some of what you get out - without our awesome registered users none of this would be possible! Plus, you get way more great stuff as a member! Lurk to lose, participate to WIN*!
  • Say hello and join the conversation
  • Subscribe to topics and forums to get automatic updates
  • Get your own profile and make new friends
  • Classifieds with all sorts of Subaru goodies
  • Photo hosting in our gallery
  • Meet other cool people with cool cars
Seriously, what are you waiting for? Make your life more fulfilling and join today! You and your Subaru won't regret it, we guarantee** it.

* The joy of participation and being generally awesome constitutes winning
** Not an actual guarantee, but seriously, you probably won't regret it!

Serving the Subaru Community since May 18th, 1998!

Guest Message by DevFuse
 

Photo
- - - - -

hesitation/stumble problem w/ 86 RX


  • Please log in to reply
23 replies to this topic

#1 Ben L

Ben L

    USMB Regular

  • Members
  • PipPipPip
  • 33 posts
  • Virginia

Posted 16 December 2003 - 07:37 AM

hey guys,
i've been enjoying my 86 RX, especially because we've gotten some good snows already this year ;) but i've been experiencing a problem with my RX.

the symptoms of the problem are that the car will have a hesitation/stumble problem, usually under light throttle/cruising. if i mash the gas it will stumble for about 2 seconds, then surge forward w/ boost. the turbo appears to be functioning normally. the problem doesn't occur more when the car is warm or cold, and it doesn't happen all the time.

i checked the EGR solenoid after getting a check engine light. sure enough, one of the vacuum lines had broken off the egr solenoid. i replaced the solenoid and vacuum line, and no more check engine codes, but the problem STILL persists.

i don't know much about these subarus, but my first thought is oxygen sensor or mass air flow. the oxygen senson was however replaced recently, it's still shiny looking, so i'm doubting that's the problem.

has anyone had this problem, and what were the solutions? thanks for any help!

thanks.

#2 RedRX

RedRX

    USMB Regular

  • Members
  • PipPipPip
  • 61 posts
  • Australia

Posted 16 December 2003 - 07:55 AM

Wish I could help, cos my 86RX is doing exactly the same thing. Murphy's law states that it will NOT me the same cause, nor will it be a single SIMPLE cause.... sigh!

Let me know if you find an answer and I will reciprocate.

#3 Dr. RX

Dr. RX

    Elite Master of the Subaru

  • Members
  • 9,984 posts
  • Sammamish, WA

Posted 16 December 2003 - 08:04 AM

Not sure if this is taht same problem, but on my wife's turbo wagon (85), the engine was dying on her at idle. I checked everything fuel related and came up empty. The the car totally died on her, the battery was totally drained, so the first thing that I thought was alternator. I always keep spares around, so I took one of the spares, replaced the one in the car, jump stared it, it ran fine. It has not had the stalling problem since. It appears that some of the electronic controls for the fuel injection were not getting the correct voltage, so they were not functioning properly. With winter coming on, batteries have an extra load on them, and tend to show their weakness, so check the electrical system too.

#4 Meeky Moose

Meeky Moose

    Subaru Master

  • Members
  • 2,343 posts
  • Grants Pass

Posted 16 December 2003 - 08:25 AM

every turbo subaru i've ever had both had surging problems.. never did find a fix..

guess i'll get to rule the internals of the engine out when i get a new one for the RX in febuary..

#5 rallyruss

rallyruss

    Subaru Master

  • Members
  • 1,653 posts
  • San Jose CA

Posted 16 December 2003 - 02:20 PM

my rx has no surge. but the wagon did. I disconected the egr vac line and pluged it and surge went away. not a real fix but thats as far as mine went.

#6 Ben L

Ben L

    USMB Regular

  • Members
  • PipPipPip
  • 33 posts
  • Virginia

Posted 17 December 2003 - 08:53 AM

i just replaced the battery about two weeks ago. i never have any problems with the car stalling or cutting off at idle.

i found that i have less of a problem if i keep the revs about 2k rpm. i would guess that the problem is somewhere in the fuel system..like i said earlier, it really feels like a bad o2 or MAF sensor, but you would think it would trigger a trouble code.

i have also determined that the wiring in the car just feels old. my clock works half the time and half the time it doesn't.

anymore ideas? this seems like a regular problem with these cars.

#7 jimkup

jimkup

    USMB Regular

  • Members
  • PipPipPip
  • 74 posts
  • Austin, TX

Posted 17 December 2003 - 09:29 AM

Sounds a little like a prob I had a few months ago.
I have an '88 Wagon, non turbo with about 220K.
She started ideling rough but would smooth out with increase RPM. Even had the "hesitation" you talk about. Suspected a misfire & pulled plug wires with her running & found #3 made no difference. Pulled plug, disconnected fuel injector, (mine is SPFI) & put wire on plug & turned her over. Spark was ok too. Put a compression tester on & was way low, only about 60 psi. Wound up replacing both lifters on that cylinder & still ok after about 2 months. May not solve your problem but worked for me. Good Luck!

#8 Skip

Skip

    Flatuous Blather

  • Moderator
  • 8,991 posts
  • Latrobe, Pennsylvania

Posted 17 December 2003 - 07:15 PM

Ben, look closely at the MAF to turbo pipe.
Cracks in the corrigations can be hard to spot.
You may want to see if the MAF vane is moving freely.
02 sensors will not trip the CEL until they are toatly toast or disconnected but I don't think that is the problem.
Your TPS is also a simple affair and rarely gives problems but it is an easy test (just contacts no varriable resistor)
I have never had a turbo surge so I am guessing
, the other possibility that comes to mind is the FPR not regulating the fuel pressure evenly, if the Fuel Pres. varried the engine may surge.
Have to connect a gage for this test (I use an electric oil pressure gage, Tee'd in after the fuel filter, the diaphragm is made to withstand gas and oil and has not given me any problems)
Hope this helps a little


#9 suba

suba

    USMB Regular

  • Members
  • PipPipPip
  • 74 posts
  • moscow, ID

Posted 17 December 2003 - 09:37 PM

i had a very similar problem on my rx when i first got it. it turned out to be tha MAF....it was very dirty and out of adjustment. it has a different air filter and box so i had to readjust it...which took me about 2 weeks of fiddling to get it right. i also took it apart and blasted it with electronics cleaner, which seemed to help a little. i also pushed the electrical contacts down to make a better connection. been working great until a little while ago, but i think i may have gotten some oil back up in it.

#10 Ben L

Ben L

    USMB Regular

  • Members
  • PipPipPip
  • 33 posts
  • Virginia

Posted 20 December 2003 - 03:35 PM

thanks all, i'll be cleaning the MAF this afternoon, i'll report if it makes a difference.

hey meeky moose, if you read this, did your HKS filter make any performance differance?

thanks ;)

#11 myossfeece

myossfeece

    USMB is life!

  • Members
  • 231 posts
  • UPinAsubaruRX, INDIANA

Posted 20 December 2003 - 03:47 PM

my rx does the same thing occasionally. after it warms for a few and the car idles down, it will fall down to 250 rpm and idles slugishly. Mimics the effect of a misfire, and all at once it will correct itself and idle back running smooth and all. I can tell when it's gonna hesitate because it will idle so low, but has never stalled because of it. I swapped maf sensor and got no difference in performance, it still occasionally stumbles. Not any more or less. godd luck with a solution.

My opinion: It's A Turbo Thing!!!!

#12 Ben L

Ben L

    USMB Regular

  • Members
  • PipPipPip
  • 33 posts
  • Virginia

Posted 22 December 2003 - 06:24 PM

well i haven't driven the car since i cleaned the MAF but it didn't look incredibly dirty or anything, and the vane moved freely. i really don't think that's the problem. :(

#13 bushbasher

bushbasher

    exhaust fume addict

  • Members
  • 1,707 posts
  • Sooke B.C. Canada

Posted 01 January 2004 - 08:43 PM

a bad connection to ground can cause the engine to run roughly, as well as dim lights, and alternator problems. I just cleaned my grounds and now my hesitation is gone (it would hesitate between 1k-2k when mashing the pedal), and my horn and lights are more powerful. My battery is also now charging, though it may be too late as its been sitting dead.

#14 Meeky Moose

Meeky Moose

    Subaru Master

  • Members
  • 2,343 posts
  • Grants Pass

Posted 02 January 2004 - 12:37 AM

hks filter made a littel difference.. alot of rumble.. scares the hondas away.. especially because they can hear that it does have a turbo...


if ya don't get this fixed, you can stop by my place or i can drop by sometime.. since your only 20 min away, lol..

#15 Ben L

Ben L

    USMB Regular

  • Members
  • PipPipPip
  • 33 posts
  • Virginia

Posted 10 January 2004 - 10:48 AM

i cleaned out the MAF and it didn't look that dirty, but it apparantly did help, the hesitation has mostly gone away. my lights are indeed super dim, i just installed some hella driving lights because it was so bad. which grounds did you clean bush basher?

meeky, we should get together sometime soon so i can check out your car ;)

#16 Skip

Skip

    Flatuous Blather

  • Moderator
  • 8,991 posts
  • Latrobe, Pennsylvania

Posted 10 January 2004 - 11:42 AM

Ben, don't mean to step on your question to BB, hope he still answers.
The one ground point that is crucial to headlight (all lights) is the ground point (bolt) on dr. side strut tower directly behind the coil.
Our head lights use a negative (or ground) switching system. The +12 from the bat is applied to the lights any time the ignition switch is in the run position. To switch the lights ON, the negative is fed to filament (hi/low) via the switch. The head lamp switch gets this ground connection fom the ground point behind the coil.
In brief - this point carries all the current needed to light the lights.
This fact was gleaned from the FSM for my car.
Hope this helps


#17 c150L

c150L

    Subaru Nut

  • Members
  • 532 posts
  • East Central Wisconsin

Posted 10 January 2004 - 01:47 PM

My 89 XT-6 (not a turbo) does exactly the same thing. Hesitations, stumbles, surges. Mash the throttle all the way down, seconds later, you can feel all 6 digging in. Going to change plugs first, probably wires, cap and rotor. Just seems like the plugs are fouling when it's doing that.

Didn't know the MAF was a vane type. Thought it was of the heated wire variety. Will try the cleaning thing on the XT-6.

What about a bad TPS. (Throttle position sensor) Between idle and wide open throttle position, isn't it a variable resistor that signals the throttle position to the ECU? If the resistance in the mid throttle position is high or low, may cause the injectorss to open or close more and send the fue/air mixture way out of whack.

On all Subes I have dealt with (<1990), if the check engine light comes on and codes point to the EGR, the EGR solenoids electrical circuit is open. Found one that the plug was off the solenoid, 2 that the coil with in the solenoid was broke/burned out. An open electrical circuit is all the puter can detect. Perhas some have an EGR position sensor that the puter gets info from, but I have not seem one in a Sube yet.

#18 Skip

Skip

    Flatuous Blather

  • Moderator
  • 8,991 posts
  • Latrobe, Pennsylvania

Posted 10 January 2004 - 02:25 PM

c150L your XT6 uses a Hot Wire MAF and does indeed have a "pot" (potentiometer) in the TPS.
This discussion is for the older style FI system that Ben's RX has.


#19 c150L

c150L

    Subaru Nut

  • Members
  • 532 posts
  • East Central Wisconsin

Posted 10 January 2004 - 03:42 PM

This discussion is for the older style FI system that Ben's RX has.



Well? (I was not trying to hijack this discussion by interjecting bad info based on the actions and possible remedies I've been thinking about using on my new style FI system that my XT-6 has.)

So when/where is the split between the older FI systems that the RX has VS the newer FI systems with the hot wire system. (I shall try and ref next time someone asks questions about one.) My 88 GL was SPFI and I'm nearly positive that one was also of the hot wire variety. The only FI systems I've come across on Subes has had a MAF of the hot wire variety, guess that's why I stated "Didn't know the MAF was a vane type". Guess I could have stated that I was not aware of any vane type systems in Subes. (Gives me one more thing to look at at the auction when I pop the hoods on all the Subes that go by.)

In the case of a vane type MAF, would I be safe to assume that it too may have a potentiometer that may short or fault in the mid range and send wong info to the ECU? Possibly cause same sort of problems that a bad TPS sensor may?

#20 Warp3

Warp3

    Eat, Live, Breath Subaru

  • Members
  • 313 posts
  • WNC

Posted 24 March 2004 - 02:37 PM

Originally posted by c150L
So when/where is the split between the older FI systems that the RX has VS the newer FI systems with the hot wire system.


Was searching the forums and realized this question never got answered.

The changeover occurred for the '87 model year (which oddly enough is when the MPFI turbos suddenly went from 111 to 115hp...lol...I'm guessing the less restrictive hot-wire MAF was at least part of that).

My '86 RX is doing something very similar to what is quoted in this thread and the MAF is one of the parts I'm guessing may be at fault (as it isn't exactly clean inside the MAF tube). I'm also considering the IAC Valve (which I recently discovered is called an Auxiliary Air Control Valve in the service manual and parts listings, FYI) as a possible culprit as well. (Partly because once the car is fully warmed up (and I mean FULLY warmed up) it doesn't seem to happen as much (if at all).)

#21 Meeky Moose

Meeky Moose

    Subaru Master

  • Members
  • 2,343 posts
  • Grants Pass

Posted 24 March 2004 - 03:30 PM

mines sugrin too. bah new engine and all.. i'll figure it out eventually..


85 and 86' years had the vane style maf, 87 and up had the hotwire maf's.. not sure if this applied to spfi tho..

#22 rallyruss

rallyruss

    Subaru Master

  • Members
  • 1,653 posts
  • San Jose CA

Posted 24 March 2004 - 05:02 PM

like I said before I had the same problem and determined it was the EGR opening too soon. I also had a small crack in the air intake boot. I replaced the boot and bypased the EGR temporarily.

#23 greggbrat

greggbrat

    Eat, Live, Breath Subaru

  • Members
  • 263 posts
  • Denver Colorado

Posted 27 March 2004 - 02:34 AM

I had a similar problem with my 87 RX and it turned out to be two different problems that happened at the same time.

First I replaced the MAF (got one from a junkyard for about $15) and the driveability improved from horrible to just poor. It would still run great if I nursed the gas pedal just right in turbo boost.

Further investigation showed a dead fuel injector.........I am thinking that in high turbo boost that cylinder was getting bleedover fuel from the other intake injectors. I used the classic screwdriver to my ear stethoscope method to find the fuel injector that was not "clicking". I replaced the injector and its now running perfect.

#24 MilesFox

MilesFox

    Catch this Fox!

  • Members
  • 10,336 posts
  • Madison/Milwaukee, WI

Posted 27 March 2004 - 10:47 AM

my rx does the same thing occasionally. after it warms for a few and the car idles down, it will fall down to 250 rpm and idles slugishly. Mimics the effect of a misfire, and all at once it will correct itself and idle back running smooth and all. I can tell when it's gonna hesitate because it will idle so low, but has never stalled because of it. I swapped maf sensor and got no difference in performance, it still occasionally stumbles. Not any more or less. godd luck with a solution.

My opinion: It's A Turbo Thing!!!!



we tried to replace the TPS with an odd one, the replacement was bad, so back to original.

it mounts with 2 screws, and if you loosen them, you can turn it one way or the other. we turned it so the car thinks the throttle is moe open, and it helped quite a bit on the low rpm part throttle




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users