Momentary loss of fuel i think

[wogden700]

Driving the car on the highway the other day I had a momentary loss of I believe fuel it was not even a second and it came back. Also associated with it I noticed some flickering of the temperature gauge on the dash. It didn't happen again the same day a little while later.
The car is in 85 635 us model all stock except a Turner chip. I had the instrument cluster out earlier this year to fix the gears and I had the batteries replaced in it and the connections cleaned up I also had a new main ground strap put on the engine and the battery terminals cleaned. Prior to that I would notice the temp gauge flickering around but never with an associated loss of fuel.


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[Bert Poliakoff]

Flickering of the temperature gauge would have nothing to do with fuel unless it is something electrical. So that opens up a whole can of worms because unless they are on the same fuse or relay or a common ground who knows? Desk top Dave may chime in here..

[RSheiman]

Many options: crack in the distrib cap, may be micro and hard to see, then fuel regulator, then coolant temp sensor, then reference sensor, then relays for pump, then in tank pump. No particular order of this incomplete list. May not end up being related but get to know http://www.hiperformancestore.com/Motronic.htm

[1986series6]

Warner,

Check out temp sensors in the thermostat housing. Make sure the connections are clean with no oxidation.

[wogden700]

Thanks for the replies. Here is an update on the situation. I drove the car over 200 miles Saturday and no issues, not even a hiccup until the last 5 miles and then it was really bad. This time I didnt notice any flickering of the temp gauge so maybe I imagined that.
But what did happen was some real bad hesitation at low throttle settings. For example, on the highway at 60 i would let off the throttle and when I eased back into it there would be real noticable bucking and hesitation. If I downshifted and stomped the gas and accelerated hard, it would go away, but would come back as soon as I got to low throttle positions. And I could hear the engine was not running snoothly. Getting off the highway the engine almost stalled, but did recover on its own after dropping to like 400rpm.
Coming away from the stoplight if i drove it hard, it would sound ok, but if I tried to drive like a normal person it would buck and sputter.
Back in the driveway it idled ok, but was a but rougher than usual. Its never been a perfectly smooth idle, but this was noticable worse. Popping the hood nothing seemed out of place and I wiggled every wire and connection i could find, nothing made a change, better or worse.
It almost sounds like it's running a little too lean, or like it has a vacuum leak. I had a motorcycle that had vacuum.leak at behave similarly, rough idle and hesitation but not this bad. So I'm thinking a vacuum leak or possibly a sensor issue.
Long post i know, but wanted to give as much info as possible.
Any ideas?
Thanks!
Ps I just started reading the mototronic guide that was posted

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[bmw6fan]

Vacuum leak is a good place to start and check the connections to the O2 sensor.

[1986series6]

Warner,

At WOT (wide open throttle) the TPS goes to ground and the ECU gives you full fuel and max timing,

ignoring any sensor input.

That's why it runs good @ full throttle.

It's the ECU not getting info from sensors @ part throttle of the TPS's potentiometer.

Check the connections on your sensors for good contact.

Also, to do an easy smoke test, I bought a bee smoker for $13

and used smoke chips to burn and puffed the smoke into the vacuum system

to look for leaks.

https://www.walmart.com/ip/Zimtown-S...ll&athena=true

Follow this to help check out a possible solution.

http://www.hiperformancestore.com/Motronic.htm

Good luck

[wogden700]

Thanks Bob. I was wondering about TPS or something like that. I started reading that article and it's really helpful. Made me realize I need to replace all vacuum lines anyway since on inspection they appear to be all original. I wont get to spend much time on it this week, but maybe an evening here or there.

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[1986series6]

Warner,

May I suggest before you change vacuum lines, do a smoke test to find a leak or establish you don't have one.

If you don't, you'll never where the leak was to correct or in fact you don't have one but

at least you'll know.

[wogden700]

That's a good point. I'll do.that

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[RSheiman]

http://bigcoupe.com/phpBB3/viewtopic.php?t=2253


Just some more reading. AFM testing

[wogden700]

Found it! From the IAC or whatever Bosch calls it is a rubber hose that bypasses the throttle body direct to the plenum. It was cracked. This was a rubber hose originally, but after 34 years it has hardened to something closer to plastic and became very brittle. Taking the intake boot off i also cracked the breather from the rocker cover that hose was so hard it shattered like pvc.
Thanks Bob for suggesting the smoke test, changing all the small vacuum lines would not have found or fixed this.
I didnt use the bee smoker, I used this DIY solution which works quite well.
I sent smoke into the vacuum line from the fuel pressure regulator that goes down to the bottom of the plenum. Took about 5 minutes.
https://youtu.be/GOhl4r0GSiE

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[1986series6]

All right Warner, way to go.

What method did you use to create the smoke.

[wogden700]

All right Warner, way to go.

What method did you use to create the smoke.

I used a little hand operated pump and stuck a cigar in the intake to create the smoke. The YouTube video I linked shows it. Works great!

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[1986series6]

Yeah,

I saw that utube video also, but since I'm a cigar smoker-I could never waste good cigar smoke

looking for a vacuum leak. lol Glad it worked out for you. See you & Marta @ the 2020 "Idiotfest"

[wogden700]

For sure! Hoping to make sharkfest too.

And dont worry, it was just a Phillies blunt, nothing good at all

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[1986series6]

Phillies blunt is now a good smoke tool.