930 with Motronics running alittle funny

[Install425]

Hello all I have a 1988 930 running Motronic, It was original built by Prototech. Its been running great for years. Recently I did a track day, ran fine all day except it was running a little hot so i wasn't pushing it. Since then about 2 months the car sat in the garage. Well took the car out the other day and noticed that if the rpms are @ 2000 to 3000 and running steady it starts to jerk, if I hammer it or just give it gas it goes just fine. I did a basic tune up Cap, Rotor, Plugs & Air Filter, Didn't seem to help. Awhile back I had a head temp sensor go bad, which made it run rich. It actually barley ran, was super rich. This is not that bad but may be a sensor is bad? Any thoughts would been really helpful. Thanks

[930gt-40r]

Did the ignition tune up affect it at all? Maybe the MAP sensor inside the computer is starting to take a dump?? Ive been up and down many paths of diagnostics with that system (including 140 mph passes with a voltmeter sitting in my lap connected to the map sensor circuit)
It also could be $hitty gas, you said you had it at the track day- did you fill it with race gas? if so run it out of fuel which ever way you want and replace with fresh 93- that may help

[Install425]

The tune up did not seem to do much. There wasn't much gas left so I filled it up and added injector clean / gas conditioner. I'll see how that goes, thanks for your response.

[DDDD]

I had a mystery problem for a while and I have suspected bad gasoline. It just seemed to go away one day. Knocking on wood.

[purplehaze]

Originally Posted by 930gt-40r

........including 140 mph passes with a voltmeter sitting in my lap connected to the map sensor circuit....

Wussie. It was no more than 135, but who's counting.

I had similar issues with my Proto system. Tuning for wide open throttle (WOT) is often easier than the around town, or gentle transition stuff.

If the issue just started (engine is warm, and the cyl head temp sensor is good), it's probably the pressure sensor or a vac leak. You might want to double check all vac lines are zip tied, no cracks, and nothing has come loose. I would always have a vac leak somewhere when it was running rough.

If it's always been this way, it's probably the tune. Assuming you've done no other hardware changes (replaced turbo, exhaust, cams, intake, I/C, etc). Pressure sensing is very sensitive to these changes, and a re-tune is usually required.

Have you rang Prototech yet? Or Todd Knighton, Protomotive?

Glad you dialed it back when it got hot. Hope you throw another cooler in it so you can get back on the track.

Good luck!

[kojo911]

my bet would be dirty injectors, if the Car's been sitting they could be gummed up. Blow a couple of bottles of techron, or redline injector cleaner w/ 2-3 gallons of gas see if that helps, if not remove injectors and have them professionally cleaned.

[BReyes]

Its definitely about cleanliness. On NA I had never had a MAF so PO may have because never had MAF issue. That said I once had similar issue and I cleaned the "micro sensors" that click coming on and off idle. There are couple valves- Look at your metal -If all shinny yellow anodized, sweet all certain to be good with any factory valves. I have had motronic brain rebuilt. Fuel pump. Distributor too.

You think it is electrical and not fuel? Sounds like you have cleaned everything. Has your distributor been rebuilt? I remember reading about Warren writing about most early cars needing distributor inspections/refurbishments because of the number of years since all were new.

[SCHNELE]

That jerking may be caused by the boost cut off switch, I am not really familiar with Todd's Protomotive setup but I imagine the engine management is seeing a lean condition and cutting boost.

[SCHNELE]

Give Todd a call I am sure he is best situated to answer your questions.

[purplehaze]

Agreed, call Todd. There's no boost cut off switch on these, and that off idle micro-sensor would give a different symptom.

At 2-3 k it's not really into boost yet, more the around town/partial throttle stuff that's hard to tune.

If you have a AFR gauge, it would help show if it's hitting a lean or rich spot as well.

[BReyes]

Also have you checked the cleanliness/gap of the flywheel sensors?

[930gt-40r]

Originally Posted by purplehaze

Wussie. It was no more than 135, but who's counting.

Kris: "Glenn stop decelling"

Glenn: "Im not doing that!"

[Install425]

All good thoughts. I've been busy, girlfriends Jeep Liberty 3.7 spun a connecting rod bearing (wonderful). So I've been working on that. I try all suggestion in a few days. Thanks for all the responses, always a pleasure asking questions on this forum.

[SCHNELE]

Damn you are not having good car luck right now. I am a Jeep Chrysler Dodge Dealer, let me know if I can help.