Understanding Bosch CIS Fuel Injection

David S.
By David S. Wallens
Sep 22, 2020 | Volkswagen, rabbit, GTI, Callaway, Bosch

If you have worked with older European cars, then you have likely encountered Bosch CIS injection. It was fairly prevalent back in the ’70s and ’80s on cars from VW, BMW, Audi, Porsche, Mercedes-Benz, Volvo, Saab and even Ferrari.

The Callaway turbocharged  VW Rabbit GTI that we’re doing over at Classic Motorsports is so blessed. When we bought the car, it was a non-runner. To get it back online, we had to dive into the CIS system.

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View comments on the GRM forums
porschenut Reader
9/22/20 1:18 p.m.

Stands for Can't Initiate Speed. Yank it and go aftermarket,

Stefan (Forum Supporter)
Stefan (Forum Supporter) GRM+ Memberand MegaDork
9/22/20 1:29 p.m.
porschenut said:

Stands for Can't Initiate Speed. Yank it and go aftermarket,

I went MegaSquirt on my Porsche 924 and never looked back.  If you read the 924 groups and forums, you'll see how many are sidelined due to CIS issues of one form or another.

Cedricn New Reader
9/22/20 2:34 p.m.

The Cis is cleverly designed, simple and reliable. But it works best in the simpler cis basic we got here without lambda control etc. But a barn find car can be some hassöe to get up and running, they work best if used sometime. Read first before you fiddle and it will save you alot of time and money :) 


Running about 240+hp in my 924 turbo with stock CIS, love efi system but not in this car :) 

Stefan (Forum Supporter)
Stefan (Forum Supporter) GRM+ Memberand MegaDork
9/22/20 3:08 p.m.

In reply to Cedricn :

Mine WAS working, it drove the car home from Bellingham to Portland about 300 miles on 3 cylinders.

It was running on 3 because the exhaust manifold cracked and one of the exhaust valves partially shattered.

It also had no working alternator.

When I went to start pulling the head, the banjo fittings at the injectors all broke (even while being supported properly), so that was the end of that for CIS.

Moving to EFI freed up a ton of space under the hood and made diagnosis much easier.

Modern fuels in North America really don't like to sit, especially in carbs and CIS systems.  They seem to gum up (likely some of the additives used) and that causes a lot of issues that aren't easy to sort without essentially rebuilding it all.

angusmf Reader
9/22/20 3:42 p.m.

Lol. Just Lol. First time back here in forever and David is talking about CIS. That makes me feel comforted beyond belief. Can't wait to read the article even tho I already pretty much know how it's gonna end! wink

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
9/22/20 3:49 p.m.

CIS works incredibly well when it hasn't been screwed with.  Rather like a Quadrajet.


I'll take CIS-E over anything with a warmup regulator any day.  It just works.  The only time I ever had issues with CIS-E were related to brittle corroded wiring in places, and bad exhaust leaks due to 6 of 10 manifold studs being broken/missing, so the O2 was wildly incorrect.  Solution for that was a zip tie on the WOT switch smiley


I'm going EFI on my Audi engine because the fuel distributors have a roughly 300hp limit, and the air valve's restriction poses a roughly 10 percent power loss.

David S. Wallens
David S. Wallens Editorial Director
9/22/20 3:49 p.m.

In reply to angusmf :

Welcome back!! It's been a while. Hope that all is well. And I had CIS on my GTI, but that was a few years/decades ago. 

Streetwiseguy MegaDork
9/22/20 5:27 p.m.

Fresh gasoline and fuel filters, no vacuum leaks, and a stock motor that hasn't sat, unmoved for over a year, and K-jetronic is lovely.

I very occasionally get to drive an old Kjet 240 Volvo, and they just run correctly.

84FSP UltraDork
9/22/20 5:32 p.m.

I spent way too much time making my rabbit cis happy with 13:1 static compression.  Also fun that now it's an interference engine, ask me how I know.  Now runs like a strong 1.8 16v in an 1850 lb car.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
9/22/20 5:38 p.m.

In reply to 84FSP :

20v pistons with an 8v head?

I acquired a '98 reciprocating assembly to do just that.

angusmf Reader
9/22/20 6:08 p.m.

In reply to David S. Wallens :

Yup! A few years or decades ago I was finishing my first watercooled swap, a 2.0 into my Pickup and was having weird running issues. Posted on the forum about it and you were like "Yeah, that sounds like CIS to me..."

car39 Dork
9/22/20 10:40 p.m.

When Volvo first got CIS in 74, it was a nightmare.  The fuel wasn't clean enough, and the filters and the injectors would plug.  Americans were used to pumping the gas pedal a few times to set the choke when cold.  That caused a backfire.  If you were lucky, only a hose would come loose.  If you were unlucky, the "bonnet" that covered the air plate would shatter.  Either way, you were stuck, since the system relied on vacuum to run.  We had one customer car that got a dented hood from the plastic bonnet blowing off the control unit.  Most of the parts needed were on back order for almost the entire year, because no one expected the issues to be as bad as they were.  Once the customer was educated, the fuel quality improved, and the parts supply issues corrected, it was a very reliable unit.  

spacecadet (Forum Supporter)
spacecadet (Forum Supporter) GRM+ Memberand SuperDork
9/22/20 11:06 p.m.

My hometown in IL has a Bosch certified shop.. they keep my buddies family SL convertible running in top shape.

only Bosch shop i've ever heard of..


porschenut Reader
9/23/20 8:30 a.m.

They do have a neat limp mode.  Hot wire the cold start injector with a switch in the car.  You can actually drive that way as long as the fuel pump is runnig.

jimbbski SuperDork
9/23/20 9:07 a.m.

In reply to Pete. (l33t FS) :

I have to agree generally.  I have an '88 Scriocco and once I figured out the ins and outs of CIS-E it worked quite well. Mine was a race car and the downside of that with CIS is that they don't like to sit unused for long periods of time. The fuel dist. on mine after 32 years finally decided to not add fuel above idle but when it worked it worked well.


LanEvo Dork
9/23/20 9:55 a.m.

This was my solution to CIS:


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