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1988 Volkswagen Cabriolet
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Discussion Starter · #1 ·
Hey all,
I'm sure this topic has been discussed time and time again, so please direct me to the right thread if available.

I have an 1988 VW Cabriolet with CIS-E and K-Jetronic fuel injection, and when the ambient temperature is warm/hot, the car will begin to struggle and die. The car has good pep and power, but after driving for 10 minutes or so, it wants to die. I've learned via cabby-info.com that fuel pumps are the go-to thing to replace to fix this issue. I've replaced the in-tank pump once and the in-line pump twice to no avail. The fuel filter, the fuel pump relay, and the fuel injection power supply relay have all been replaced as well. Pic for attention.
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I have an 1988 VW Cabriolet with CIS-E and K-Jetronic fuel injection...
If you're running any engine other than the one found in a 16V Scirocco then you're running CIS-lambda, not CIS-E.

Best practice is to replace both pumps at the same time. And yes, your pump(s) could cause this issue. The best way to isolate CIS-related issues is to run a fuel pressure test which you might want to consider doing before throwing more parts at this problem.

What fuel/air mixture (duty cycle) are you running?
 

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'81 Trek 614, '95 Ranger
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Injector cleaning and seal replacement;

You didn't spend enough time at cabby-info
You're gonna need a DVOM capable of displaying duty cycle and/or dwell. Grandpa's old dwell meter will suffice as will cheap digital meters, no need to spend large here.

Ignition timing and ignition advance mechanisms are not to be overlooked.

NGK plugs and wires, Bosch cap and rotor.
 

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A simple test will determine if the in-tank fuel pump works. Just because you replaced it does not mean it works. I personally replaced two in-tank fuel pumps with a combined running time of an hour or two.

Do not use Vemo pumps.
 

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Hey all,
I'm sure this topic has been discussed time and time again, so please direct me to the right thread if available.

I have an 1988 VW Cabriolet with CIS-E and K-Jetronic fuel injection, and when the ambient temperature is warm/hot, the car will begin to struggle and die. The car has good pep and power, but after driving for 10 minutes or so, it wants to die. I've learned via cabby-info.com that fuel pumps are the go-to thing to replace to fix this issue. I've replaced the in-tank pump once and the in-line pump twice to no avail. The fuel filter, the fuel pump relay, and the fuel injection power supply relay have all been replaced as well. Pic for attention. View attachment 209585
 

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My 88 did the same thing. It was the warm-up regulator gummed up. As the temperature goes up it adjusts the control pressure in the upper chamber of the fuel distributor. I opened mine up and cleaned the screens and removed some fuel resin from steel diaphragm inside. As others mentioned, you should check other items as well.
 

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2007 Volkswagen Jetta 2.5L, Wolfsburg Edition & 1988 Volkswagen Cabriolet 1.8L
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Use only Bosch brand in-tank and in-line pumps. Replace all 4 fuel injectors (Bosch, look up the brass Mercedes injectors), seals and seats. Backflush your fuel lines/fuel distributor with compressed air. Went through this song and dance when I first got my Cabby in 2019. Dying when hot is the fuel pump(s) 9/10.
 

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1988 Volkswagen Cabriolet
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Discussion Starter · #8 ·
Hi all, thanks for the input. I've spent a lot of time scouring cabby-info.com, and the recommended fix was pumps. In-line pump is Bosch and in-tank pump is URO Parts. I don't have a method to test the overall fuel pressure yet as I don't have a tester/haven't built one. I'll check out the duty cycle and report back. I was told when I bought it that injectors, cap, rotor had all been replaced previously. That's all with a grain of salt, but I'll start digging around in there as well as the warm up regulator. Off to the garage!
 

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Discussion Starter · #10 ·
Took apart a number of things to get some visibility. Here is the bottom side of the distributor. Probably needs a cleaning.
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This is the top side of the airbox. Interestingly, there is no mixture adjustment screw anymore. Duty cycles was about 30 degrees (a bit lean).
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Duty cycle needs to be taken with a grain of salt as I have not been able to get my idle below about 1200. My throttle body gasket leaks badly, and the bolts are currently seized. Any idea besides PB Blaster to get those out? It's likely contributing to a lean mixutre. Also, any idea what the length and thread pitch of the mixture adjustment screw is? Thanks for the help everyone!
 

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Interestingly, there is no mixture adjustment screw anymore.
Have you visually verified this? Sometimes the head of that 3mm hex screw gets covered with debris so when you slide your hex wrench in it fails to engage the screw.

Duty cycles was about 30 degrees (a bit lean)..needs to be taken with a grain of salt as I have not been able to get my idle below about 1200. My throttle body gasket leaks badly, and the bolts are currently seized. Any idea besides PB Blaster to get those out?
1. Looks like you're measuring dwell, not duty cycle. The 30 degree reading indicates that your engine is running a rich mixture which makes sense given that vacuum leaks are present - CIS attempts to compensate for these vacuum leaks by richening up your mixture. You'll need to cure those vacuum leaks before you can adjust your fuel/air mixture.

2. About those bolts, soak overnight with Berryman's EZ Doz It (perhaps for 2-3 nights).

Good luck.
 

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Discussion Starter · #13 ·
Have you visually verified this? Sometimes the head of that 3mm hex screw gets covered with debris so when you slide your hex wrench in it fails to engage the screw.



1. Looks like you're measuring dwell, not duty cycle. The 30 degree reading indicates that your engine is running a rich mixture which makes sense given that vacuum leaks are present - CIS attempts to compensate for these vacuum leaks by richening up your mixture. You'll need to cure those vacuum leaks before you can adjust your fuel/air mixture.

2. About those bolts, soak overnight with Berryman's EZ Doz It (perhaps for 2-3 nights).

Good luck.
1. Thanks for the help. This injection system is still pretty foreign to me. I'm going to try and get a smoke test soon to help narrow down any remaining leaks. It had several prominent ones before.
2. I couldn't find Berryman's EZ Doz It anywhere. Even Amazon gave me the run-around. I was able to find Kano-Kroil, and that seemed to have helped. All bolts are free and none broke.
3. Any idea what size bolt I need to be looking for for that mixture adjustment? It's definitely not there anymore. I never saw one in the air box, so I wonder if it was accidentally removed in years past.
- I know we're looking for a socket cap bolt with a 3mm cap, but do you know the thread pitch and length of the shaft?
 

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Any idea what size bolt I need to be looking for for that mixture adjustment? It's definitely not there anymore. I never saw one in the air box, so I wonder if it was accidentally removed in years past.
- I know we're looking for a socket cap bolt with a 3mm cap, but do you know the thread pitch and length of the shaft?
Alas I have no idea what the specs of that adjusting screw are. And you're going to need it to properly tune your engine (adjust fuel/air mixture).

I'm surprised that VW engineered that screw such that it could be removed because why would you? If the hex head got dirty then clean it but no need to remove such an important and easily lost part.

Your best bet now may be to try and source a replacement air flow box from a junkyard or ebay. Check car-part.com for options. Good luck.

 

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Discussion Starter · #15 ·
Alright, after a couple days, I've found out some more information. I found the original bolt for the mixture adjustment, it was so covered in dirt and grime that I couldn't tell it was there. I ended up taking the whole assembly apart and cleaning it all out.
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For what it's worth, I would not take it apart again, but its back together and free moving. The bolt is pictured here.
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It's back in the car, and tuned to just about the right mixture.
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Even so, after just idling away, it stumbled and died on its own anyway. Seemed to run better, but died. I'm it's related to the ignition system now. How often do people see the ignition coil go bad? Does the ignition switch in the column have a load while driving? Or just while starting? What parts in the cap and rotor typically fail? What brands would you recommend if I can find something wrong here?
 

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How often do people see the ignition coil go bad?
I'd check for spark at the coil and #1 spark plug next. Looking for strong, consistent spark at both places. I'm assuming that timing is at/close to spec. If spark is fine at the coil and distributor (plug) then a fuel pressure test is waiting on deck.

What brands would you recommend if I can find something wrong here?
Bosch.

Other thing is that the position of the plate on your air flow box is rather important for CIS to function properly. But let's set this aside for now and focus on fuel and spark.
 

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Never seen a VW coil go bad. Never seen a distributor cap/rotor cause an intermittent stall. I have recently replaced my hall effect sensor in my distributor for an intermittent stall. Eventually it got so bad is turned into a no start problem. It's what happens when your car is telling you to work on it. At some point, you are forced to.

The ignition system is pretty darn easy to diagnose but it does take time and a good test light and volt meter. You are dealing with 30-40 year old parts so anything can go bad.
 

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Never seen a VW coil go bad.
Never? Ever? :) I've changed my coil once (it was the original coil that I replaced) in 25 years so not a common point of failure. Anyway, it takes < 30 seconds to test for spark at the coil so why not?

Never seen a distributor cap/rotor cause an intermittent stall...You are dealing with 30-40 year old parts so anything can go bad.
Agreed. OP has replaced pumps recently so distributor, timing, ignition switch, incorrectly adjusted air flow plate if that was tinkered with...
 

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Never but that does not mean they do not go bad.

FYI, I just replaced my second ignition coil on a 88 S Class because of a no start, just last week.

I have replaced ignition controllers, hall effect sensors, and ignition amplifiers.

I am a fan of testing. The ignition system is too easy not to test. There are way too many shot gun blasts around here. I suspect it's more like two seconds to test a coil. Have your, soon to be ex-friend, hold the coil wire while you crank over the engine.

What works for me is a test light. One end goes to the positive side of the coil, the other end to the negative side. Crank over the engine. The light should flicker. If it does, then the coil is bad [if you determined there is no spark]. If it does not, then the primary side of the ignition should be looked at. While the test light is on the coil, that is a good time to make certain the coil has power.
 

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Discussion Starter · #20 ·
Finally took another look after a couple frustrating days. Coil sparks well, as does spark plug #1. I've been watching the dwell each time I test something, and I noted it tends to go back to a rich mixture. For awhile, I can correct it on the fly, but eventually, it runs away on me. I then thought perhaps the O2 sensor could be giving faulty readings, but it read pretty consistently the whole way through. That said, I think we're back to vacuum issues. I'm sure I have several, but now I'm thinking of going end to end and replacing every piece. There's a particular piece that starts from the intake manifold and has 2 ports on one side. Any idea where to get this mysterious part?
 
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