1988 CIS problem

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Trouble cabby
Posts: 3
Joined: Sat Nov 01, 2014 5:24 pm
What year is your cabby?: 1988
Do you own a Cabriolet?: Yes

1988 CIS problem

Post by Trouble cabby » Sat Nov 01, 2014 5:40 pm

New to the forum. Figured I'd hit up the experts for a bit of advise. Helping out a friend and have his 88 Cabriolet in my shop. Haden't run in years. I rebuild the fuel distributor and it fired right up. It bogs down badly when I accelerate. If I'm under the hood and pull up on the sensor plate of the air flow sensor to operate the fuel distributor manualy as I work the throttle it runs perfectly with instant throttle response. Hook up the tube to the intake, back to bogging down. It's as if the engine can't lift the plate on it's own. I've found a couple vacuum leaks and fixed them and all timing marks line up. Regardless where the timing is it is the same results As far as me, I'm an old carb guy so the fuel distributor was no problem with the new kit. But sInce I'm an American car guy, I'm new to VWs And i'm hoping there is a known trick I'm overlooking. Thanks in advance!

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Briano1234
Whats that smell?
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Re: 1988 CIS problem

Post by Briano1234 » Sun Nov 02, 2014 7:52 am

Whilst I don't comment on pro's who may be getting paid to come in to forums for assistance as you have TSB's and things to assist you with, as well as manuals.

This is typical of a cabby with vacuum leaks and a duty cycle adjustment that is terribly off.
Last hint. On the back of the throttle body is a 7mm brass screw. If that is finger loose as you can turn it with your fingers then that is a vacuum leak and you need to count the turns it takes to remove it replace the o-ring and return to the original count.

I would also suspect the o-rings for the injectors as being a possible vacuum leak as well.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
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kamzcab86
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Re: 1988 CIS problem

Post by kamzcab86 » Sun Nov 02, 2014 1:34 pm

Trouble cabby wrote:Helping out a friend and have his 88 Cabriolet in my shop. Haden't run in years.
CIS does not like sitting. The first course of action with a car like this is to drain the fuel tank and put fresh gas in it along with a new fuel filter. Second course of action after you get it running is to run a product like Sea Foam through the system to help clean up the varnish. Third is to replace all other fluids and filters.

If the airflow plate isn't operating on its own, there's a potential issue with the control plunger and/or the plate is out of adjustment. Your friend should have a Bentley Service Manual for the car; if not, for shame and you should get your hands on one (library, etc.), or the Bosch Fuel Injection book by Charles Probst. In both are instructions and illustrations for checking and adjusting the control plunger and sensor plate (sorry, not retyping all of that here, and do not attempt to adjust either one on the fly; they are precision components that require exact placement).

Other potential problem areas:
  • Air-fuel mixture (aka duty cycle) is incorrectly adjusted (this should be checked each and every time any component related to the fuel system is touched: http://www.cabby-info.com/cis.htm )
  • Fuel injectors are clogged (remove them to test their spray pattern and volume; if they prove to be good, replace the O-rings and reinstall, otherwise clean them until they spray properly, replace the O-rings, and reinstall, or buy new injectors)
  • Vacuum leaks ( http://www.cabby-info.com/engine.htm#Vacuum ); clogged air filter
  • Cold start valve is leaking (test it per manual instructions)
  • Fuel pressure is out of whack (test the fuel pressures - cold, warm, control, residual - according to manual specs)

Trouble cabby
Posts: 3
Joined: Sat Nov 01, 2014 5:24 pm
What year is your cabby?: 1988
Do you own a Cabriolet?: Yes

Re: 1988 CIS problem

Post by Trouble cabby » Wed Nov 12, 2014 11:59 pm

Thanks for the help so far guys. A little more info on the car, it came to me with a brand new tank (never had gas in it) and both pumps new, fuel filter too. He had it at a mechanic who replaced most of the Jetronic components with used parts. Clearly at least the fuel distributor was bad because it now runs since I rebuilt it. And runs great if I pull up the sensor plate and work the throttle at the same time. I checked for more vacuum leaks, no more found, and it passed the starting fluid test too. I previously pulled the injectors to clean them up because they were terrible and used the old o-rings because they were still pliable. I went ahead and replaced them last night just to be safe but no change. Prior to the fuel distributor rebuild it would give a short rev off the fuel from the cold start injector. Now it's slow to start and definitely likes being hot more than cold. I'll continue with the adjustments but wanted to keep the brain-storming going. Thanks again and I'm in the St. Louis area if there are any experts local.

Trouble cabby
Posts: 3
Joined: Sat Nov 01, 2014 5:24 pm
What year is your cabby?: 1988
Do you own a Cabriolet?: Yes

Re: 1988 CIS problem

Post by Trouble cabby » Fri Jul 17, 2015 3:27 pm

I never like a post that isn't finished so here I go. Air/fuel mixture is all it turned out to be (after rebuilding the fuel distributor and injectors that is). Since the base for the sensor plate that was on the car wasn't drilled to make the adjustment I switched it with the one that was previously removed from the car. It ran much different and much better except for the black smoke. Dialed in the ratio and it runs great.

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Briano1234
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Re: 1988 CIS problem

Post by Briano1234 » Fri Jul 17, 2015 4:57 pm

thanks.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
You can lead a user to a link, but you can't make him Click.... :screwy:

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