This question is posed to oldschool because I know he loathes CIS injection as much as I do but anyone can feel free to weigh in because I’m stumped; and have been for months. This is lengthy but I’m trying to provide as much info as possible.
Car is an '83 SAAB 900 Turbo 2.0 and I’ll clip sentences to avoid eating up the 'net.
It’s been sitting for several months as I’ve had other fish to fry but it irritates me to no end. An attempted start this evening went nowhere.
STORY. Ran well every day. Drove it one Sun. A.M. no problem. Decided to pop the converter off to see if there was any clogging. Easy to do, some clogging, so I replaced it with a clean used one I had. Test drove 5 miles and it ran great. Two hours later, start and die. After doing this 4 or 5 times it would then crank over but would not start, cough, or anything.
WHAT’S BEEN CHECKED. (starting with CIS)
Fuel pressure normal, filter near new, fuel volume fine.
Cold Control Pressure fine.
Warm Control Pressure fine.
Compression. (170 PSI across the board)
Near new plugs/wires.
Hot spark.
Power at the coil in both START and RUN switch positions.
No vacuum leaks at all.
Timing chain marks, distributor, etc. all checked with no problem.
Turbocharger spins freely.
Ignition switch fine.
Fuel distributor clean as a pin, no sticking plunger, no sticking air metering plate, etc.
Pump relay jumped and with air plate lifted all injectors spray.
Wire harness checked for biodegrading, correct voltages here and there, etc.
All of the above have been checked and rechecked a number of times along with doing things like bypassing the ignition switch and swapping parts (fuel dist. control pressure reg., warmup regulator, ignition module, ign. distributor, etc.); the latter being especially irritating because I don’t like becoming a parts swapper. (It’s free from my parts stash, but still.)
The car can be cranked on for 10 minutes without a cough unless carb cleaner is sprayed into the intake then it’s good for a second or so.
To me, it almost acts like there is a large air leak between the throttle body and the air sensor plate which is then preventing engine suction from raising the plate against the fuel pressure. Complete diassembly of the entire intake tract does not show even one tiny crack, loose clamp or anything.
I know these cars and CIS pretty well but this one has absolutely stumped me, which in turn makes me feel pretty ignorant along with royally ticking me off because I don’t like getting whipped.
Anyhoo, there it is in case anyone wants to make a stab at it. I hope I’ve provided enough info and truly appreciate any suggestions or even wild guesses. Time to finish off that bottle of Cabernet in the fridge.
The replacement converter isn’t plugged?
Or collapsed?
No, the converter is fine. The converter on these models is very short in length (about a foot) and simple to change. One can eyeball straight through the honeycomb from one end to the other.
It actually ran even better after the converter change. That’s what’s ticking me off so much. It sat for a measly 2 hours after the test drive and has not run since.
With my limited knowledge on CIS, I’m thinking on what you were thinking about a large enough air leak in the intake duct to prevent the metering plate from rising. Did you check the plugs after a cranking session for evidence of fuel?? Since you can jumper the pump and get fuel from the injectors when manually raising the plate we know that fuel is capable of reaching the cylinders and spraying carb cleaner in the intake fires the engine so it is fuel related. Now, if the plugs are dry we know the plate isnt rising. Thats when I would tap the top of the intake duct at the metering box with my hand while someone else cranks it to see if the plate will pop up. Can you put a vacuum guage somewhere on the intake duct and measure vacuum during cranking to see if there is a leak in the duct somewhere that you might not have seen??
transman
4450, I really thought I would easily pick up something you missed when you went through the free control head plunger, or the plate that is connected to the arm that pushes up on the control rod can come completely disconnected, or air leak on the way to the intake, but you have all that under control.
If I had this car in the shop I would have those injectors off and looking at their spray pattern and at what point they start to spray and if they dribble with pressure. This is pretty much impossible without the injector test jig. What about a fuel pressure accumulator bleeding down? Of course we have all seen poor spray patterns without such extreme symptons. Let me think some more. I got fired over one of these CIS systems on a 84 320i,customers name was ‘Duarte’ funny how you remember these things. Guy that fired me got fired himself some months down the road and could not handle life anymore without his Service Manager status, so now he is really gone,by his own hand. I diverge like this not out of drama but just to show I know how CIS can get to you like nothing else.
Do you still have your specialized CIS fuel pressure gagues? I don’t even know where mine went and they were expensive Snap Ons.
As I leave I dwell over a fuel injector issue or the accumulator.OH I see you did the spray test, getting a little tough here. I ask was SAAB done with points is 83? BMW carried them almost to 80.Is CO adjustment with that screw on the head? I must think on this, you really have been through it.Run a valve adjustment on it just for fun (you probably don’t have any pucks though.
Last thing I can think of is I have seen that little wheel on the fuel metering rod arm sieze up.
Does this car have that removable cover over the fuel pump? The pump sits in a little tub (perhaps the tub was done as a recall item) Well since we are at a dead end pull that cover and look at the pump set up,could not hurt.
A follow-up to answer some questions.
At cranking speed the injectors do not spray unless the air sensor plate is manually lifted a tiny amount. Engine suction alone will not do it. I’ve even performed a smoke test on the intake tract with not a hint of a leak. The plugs are dry.
A vacuum gauge will show some vacuum but since the engine will not start it’s pretty iffy due to a bouncing gauge needle. There is one oddity that I can’t figure out. With the intake tube disconnected at the air cleaner housing, the throttle plate open, and a hand cupping the tube to block it off there appears to be little suction when the engine is cranked over. Theoretically this should point to an intake tract leak but a total disassembly for inspection and smoke test show nothing at all.
I’ve whacked (lightly) the fuel distributor and even changed that twice. The small roller on the air sensor plate rotates freely.
Yes, I’ve got the specialized fuel pressure tester and all pressures are correct. The fuel pump is new. (another WAG on the chance the old one could have been hiccupping even though the pressures with it showed fine)
The distributor is electronic ignition and is pretty much dead on with what VW used at the time, both as to the dist. and the module. Changed both of those too! All other CIS parts were changed over from a known good parts car with the pump being the one new item. Symptoms remain the same.
What throws me is that it ran great and 2 hours later, nothing. At first my thought was an injector leaking off (very common) and the engine was flooded but that wasn’t it.
This problem became an irritant at first, then it was pxxxxxx me clean off, and now it’s become almost comical.
I know it’s fuel, or lack of, related and I’ve seen some oddball CIS problems but this one has me totally baffled. Thank all of you for suggestions and if something comes to mind feel free to throw it out there. My brain has backtracked dozens of times and I’ve gotten nowhere.
(Can you imagine going through this in a shop setting on flat rate? And some car owners think things are cut and dried) 
That’s pretty tragic about the service manager doing himself in. There’s a ton of pressure in that position as the SM gets it from every direction. It’s a miracle that it doesn’t happen more often.
Just to be sure, you might disconnect that converter and try it.
“It actually ran even better after the converter change. That’s what’s ticking me off so much.”
The enhanced performance and some brisk driving added extra stress on some part that was on its last legs and about to fail anyway.
“a hand cupping the tube to block it off there appears to be little suction”
A plugged converter will stop the engine from drawing air in as well as pushing air out.
I second Rod Knox’ recommendation.
I too am only a novice with CIS systems. My wife had a 77 VW Scirocco that I used to maintain. Other than lubricating the fuel metering rod and replace a clogged injector, it never gave me problems.
At cranking speed the injectors do not spray unless the air sensor plate
is manually lifted a tiny amount.
That comment is the one that I’m pondering the most. Is the sensor plate not opening because of insufficient vacuum? Or is it not opening because of abnormal resistance in the CIS unit?
I’m assuming this is engine has a timing belt and the belt is intact (IE, the valve timing is good).
If you manually “wedge” the sensor plate open a bit, (causing the injectors to spray), will the engine run?
If the metering rod is frozen, I believe the sensor plate will not open. Does the metering rod move freely?
I agree - this is a tough one.
Update: Thinking a bit further, I’m wondering if something could be causing weak vacuum. For example, would a ruptured vacuum brake booster diaphragm lower the vacuum enough to cause the sensor plate to not open?
Rod Knox and Circuitsmith may be onto something.
Since a restricted exhaust will cause a low vacuum, could you have an exhaust restriction in the converter, muffler or collapse of a double-lined pipe?
Agreed that an exhaust restriction would cause something like this but I don’t get how it was running fine up to the moment I shut it off.
Just for hoots, I’ll pop the converter loose this evening since it only takes about 5 minutes, give it a shot, and see what happens. Will post back this evening but my optimism left town quite a while back.
I’m thinking that its a combination of two things:
Since you say the vacuum is a bit low, you probably need to check and set the valve clearances, as that is typically what drops it low.
Second, since the problems didn’t start until after the converter was swapped out, why not just swap it back in, and see if that restores the performance. Its possible that the additional back pressure the old converter provides sort of makes up for the low vacuum.
BC.
Whoops, forgot a few answers. The air sensor plate moves freely. The only resistance is fuel pressure and the pressure is normal.
The timing chain is good along with the chain guide and it’s in time. I removed the valve cover and inspected all of that while making sure the chain has not jumped, etc. The chain guide is also a fixed model that does not rely on engine oil pressure to maintain tension.
There are few vacuum lines on this car but I’ve already weeded that out by pinching off all vacuum sources to dashboard controls, the overboost switch, the brake booster, etc. None of it made any difference at all.
I can’t wedge the plate open as the intake boot has to be in place for the system to work and I would be afraid that whatever was being used as wedge might then get inhaled into the engine.
Yes, the metering rod (fuel plunger) operates smooth as silk.
The CIS systems have generally had their problems but it’s usually not hard to figure out.
Most problems are due to faulty injector spray patterns, dribbling injectors, injector seal leaks, and cantankerous control pressure regulators.
Whatever it is, it sure makes me feel pretty inept and to be honest it embarasses me to even hint for help from anyone. I prefer to work everything out myself but in this case…
I did check the valve clearances about 2-3k miles back and SAABs are pretty good about staying put once they’re adjusted with checks recommended every 15k miles anyway. The compression is good at 170 PSI on all cylinders.
I don’t get how it was running fine up to the moment I shut it off.
The guts of the converter shattered as it cooled off?
Maybe a foreign object or part of a pipe wall has wedged itself in the path?
The converter was removed tonight and it appears to be fine. I can see right through it with no honeycomb clogging at all. I’ve even seen CIS vehicles with gutted converters that would run fine. Another SAAB I used to own (also a CIS 900) had a gutted cat.
The attempted startup was put on hold for now. The gasoline (about 3 fresh gallons added about 3/4 months ago while checking the tank for contamination) is already starting to develop a hint of going stale by the old varnish smell. A sample will ignite but it seems to smoke more than normal. I’m going to pick up a fresh jug tomorrow. (closest station is 15 to 25 miles away depending on the time of evening.
The gasoline is not the issue though because it’s acting up even with fresh gas.
JoeMario made the comment about wedging the sensor plate and I had forgotten all about doing something similar. The pump relay was jumped, key in the run position, and I used the long 3 MM sensor plate adjusting tool to raise the sensor plate. This is inserted into the small hole, canted sideways, and this provided enough of a bind that the plate can be raised with the tool and with fuel pressure present.
The most it did was start for a second and die. After several tries with the same results eventually it became an engine cranks over but will not cough situation.
I’m going to pick up some more gasoline and give it a shot but I’m not optimistic at all because I’ve been through this routine more times than I can even remember.
Well, added some fresh gas to it last night, charged the battery up a bit, and same old, same old.
It fired right up and sounded great, for about 2 seconds. After that, crank over with no cough or sputter at all. Those familiar with CIS know that the cold start valve is responsible for the original startup and the CS valve only operates for a few seconds with much depending on the ambient air temperature.
This car can sit for 2 or 3 weeks and it will start right up - one time.
I forgot to mention it earlier but in the past I’ve even checked the pop off pressure on all of the injectors to make sure it’s not taking an excessive amount of pressure to open them up. Even changed all of the injectors just for the heck of it even though the injectors all opened when they should.
So at this point it’s obvious the air sensor plate is not rising and uncovering the fuel slots in the fuel distributor (which has been changed twice; again, for the heck of it)
The plate, hinge, roller, etc. is all free, not a sign of an air leak anywhere, fuel plunger is free, etc.
There is a vacuum valve and a vacuum switch in the intake tract and these have been ruled out by tests also.
As I said, this started off as an irritant, graduated to pxxxxxx me off, and has now moved on to being almost amusing in a way. Anyway, thanks for any suggestions as everything is considered and tested. I keep thinking this is something blatantly simple and when, or if, it ever gets sorted out I will post about the cause. In the interim, I remain lost…
OK:
The other day you wrote:
At cranking speed the injectors do not spray unless the air sensor
plate is manually lifted a tiny amount. Engine suction alone will not do it.
Are you comfortable there’s sufficient vacuum during cranking?
If not, here’s an easy (albeit far-fetched sledge-hammer style) hack to try.
Could you park a good-running-car with strong manifold vacuum next to this SAAB, and then tap into the running car’s vacuum while you’re cranking the SAAB?
As far as the cold start valve, if I recall correctly from my VW shop manual, that valve enriched the mixture when cold by supplying additional fuel spray. This “addition” was over and above what the individual injectors were normally providing.
I remember taking out each injector, one at a time, to see its spray pattern. There was fuel spraying out. Unfortunately I don’t remember if it was during cranking or if the engine was running. I believe those injectors should be spraying during cranking.