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strange stutter after 5 minutes[200/1986] posted by Richard Langis Jr. on
Thursday, 14 October 1999, at 2:57 a.m.
When it's cold - or hasn't been run for an hour or two, after 5 minutes of running the car does a little stutter then runs fine from then on.
What it almost seems like is that there's a choke or something that disconnects after a certain amount of time and then it recovers.
If I turn it on and let it idle, you can hear it do the stutter-step...the idle drops 4-500 rpm and then just comes right back up. During acceleration it's more of a bucking as the car suddenly nearly dies and then gets back on the gas.
Any ideas? BTW my Bentley came in the mail today so now I can do proper diagnostics after I get SOME idea where the problem lies... ;)
---Richard (Hillsboro, OR)
Volvo Experience
Re: strange stutter after 5 minutes[200/1986] posted by allison on
Saturday, 16 October 1999, at 9:48 a.m.
Check your O2 sensor. In fact you have the exact same FI as my 85. THat car did something very similar at 2-3 min. It would start fine, then at 2 min it would begin to chutter and almost flood out-you could smell the gas everywhere. Then the car would get through it at about 4 min, and straighten out and run without trying to stall or anything.
After thinking for an evening, because this all happened at once, here's what I guessed(and correctly). The O2 sensor is a heated wire sensor on the LH2.2. Until it reaches a certain temp(like previous sensors) the ECU operates on a closed loop. At aprox 2 min it is hot enough to start sending info to the ECU, at which point opps goes to open loop. The O2 was sending innacurate info, saying"we're running lean, lean lean". The ECU would richen the mixture untill the car was flooding. After a few minutes the ECU recognizes that there is a problem, because the signal is staying the same , and goes back to closed loop. And the car begins to run OK, but not like it really should. Pretty sophisticated, actually.
Well, I checked the voltage on the O2 sensor through the warm up problem, and sure enough, the voltage was at .5 on closed loop, and then dropped to .1 on open loop, at which point the car began to chutter and flood. I pulled the sensor to find that the tip had somehow broken off, leaving only a little point. REplacing the sensor cured the problem.
Here's the crappy thing. They are expensive. I did get mine( a Bosch part) from Advance, because they claimed the lifetime warranty thing. It was 120$. Elwhere they often want 150$ Advanced tried to be crappy when I took it back 15 months later saying oh, the y are changed at 30K, but I stuck my guns, and they gave me a new one. There wasn't anything wrong with old one, I don't think, but warranty was warranty. Any way, look at the Bosch no, and try BMW independent suppliers. I use them occassionally too.
So be sure you need the damn thing, though I'm guessing you do, after 13 years. Use an electronic Voltmeter, because the thing has to give very fast readings(old style or test light won't do). With the car cold, hook the posi side to the green single connector, and ground on the strut housing. Start the car and watch, after 1-2 min the ECU and sensor should start chatting. The voltag should bounce between .1 and .9 rapildly. If they don't, you sensor may be lazy(so watch until the car is t normal op temp), or it may be completely broken, or the wire between the two is broken. If it nver goes above.5, you also have a problem. Also check the resistance in the pre-heating part, which will be the 2 wire harness clip next to the single green wire. Be sure the ignition is off, and disconect harness clip, and resistance should be 13ohms hot, 3 ohms cold. If not, the preheater has failed.
Good luck.
Allison