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Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

I'm at the end of my rope trying to diagnose the poor running of my 1980 924 NA.

Bit of background - it runs perfectly when warm. No missing, no hesitation, no stuttering, starts perfectly and instantly at any temp.

My issue is that it runs very badly when cold which progressively directly in proportion to engine temp.

It starts and runs, but idles too slowly (about 750-800) and stutters when trying to rev up as if it's too lean and there's not enough enrichment occurring. When warm, it idles at 1,000 rpm so I don't want to speed the idle up.

I tested the AAV and it performs as intended - open in the fridge, closed under a hair dryer, partially open at room temp and measure correct resistance across the coil - although it;s the cold performance that is bad, so the coil and it;s warm up is kind of irrelevant as the poor running is from the moment it fires.

As it fires instantly when cold and stays running, I know the cold start valve is also working - a device that only really influences the first moments of running I believe?

Here is a post from another forum where I'm trying to find possible solutions to the problem.

I stripped and rebuilt the WUR believing that to be the issue and made it adjustable in the process, but before I tested the fuel pressure and new adjustable WUR, I eliminated as many variables and unknowns as possible.

I drained the tank and added a gallon of fresh fuel.

Then changed the oil, oil filter, plugs, plug leads, distributor cap, rotor arm, air filter and fuel filter.

Whilst I had the plugs out, I did a compression test which showed them all to be well within spec.

So, with the service complete, I removed the fuel pump relay and bridged terminals 30 and 87 to a switch so I could remotely operate the fuel pump without having to run the motor.

I then fitted the pressure gauge and valve between the fuel distributor and the WUR.

The WUR is buried deep down the back of the engine, mounted to the rear of the inlet manifold, hence my desire to be able to adjust it without having to remove it each time. I've got removal and refit down to about 25 mins total. It's not a sport I intend to take up professionally.

First thing to do was to test the overall system pressure by closing the valve in the test line and running the fuel pump which showed 4.7 bar which is within the range given by the k-jet bible of 4.5 - 5.2 bar.

I let the system stand for a 30 mins over lunch and it didn't drop to below 1.8 bar showing a healthy pass on the leak down test.

Next was to test the cold pressure by running the pump and seeing what the WUR was regulating to. First though I had to see what the ambient temperature was...

About 16 degrees according to the house thermometer...

But to make sure, I double checked with a proper pyrometer to confirm the results...

Which according the the K-Jet bible under the 924 section shows I should have a cold pressure of 1.35 bar.

If you recall, I'd set the post well below where I anticipated it would need to be to give me the chance to gradually draw it out on the adjustment nut, hence the first test showed what I expected - pressure below the spec required...

This is where the effort of making the unit adjustable paid off, as I was able to simply wind the nut down which effectively pull sup the insert to adjust the pressure to my desired 1.35 bar.

Which resulted in the desired 1.35 bar.

Next it was time to connect the heating coil, start the motor and check the pressure when at operating temperature.

Plenty warm enough (fan on, thermostat open, temp gauge central)...

Resulting in a warm control pressure of 3.5 bar which is within the 3.4 - 3.8 bar of where the K-Jet bible says it should be...

So far we know...

All the service items have been replaced.

We have fresh fuel.

We have good compression.

We see no leaks at the injectors.

The cost start valve/injector works as it fires straight away from cold.

The aux air valve works and has been tested hot and cold as well as resistance over the heating coil.

The system pressure is within spec.

There are no leaks on the leak down test.

The cold and warm pressures are within spec and prove the WUR is working.

It idles when warm at 1,000 rpm on the nail so the idle speed is correctly set.

So how does it run from cold?

[youtube]gTl4WtWtuKg[/youtube]

Crap.

There's no fast idle and feels like it's idling too slow with lots of vibration as if it's laboring and when I try to rev the engine, it stumbles in a kind of "B-B-B-B-B-vroooom" like it's missing slightly and hesitant.

Exactly like is was before and exactly like there is insufficient fast idle or enrichment.

As far as I can see, I've done everything possible to ensure it should run in a 'factory' manner, yet nothing has changed, which to me suggests the issue lies elsewhere.

But where?

Thoughts appreciated, keeping in mind that when warm, it starts, runs, drives and accelerates perfectly, so whatever is wrong, is not impacting the warm running.

Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Might have found the problem...

I just sprayed a load of brake/carb cleaner around each injector and on one of them there was a change in engine note and on another such a change that it nearly cut out.

I guess that'd cause my cold running issues?

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

CIS hates vacuum leaks. I'd smoke test the intake and get everything sealed up.
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WeiBe (1987 924S 2.5t) - 931 S3

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

Did you stick a wideband up its arse to see whats the mixture doing while its b b b b b-ing? I bet its rich, either because some vacum leak or because of bad mixture setting. Check all the intake hooses for cracks and leaks.
If you dont have a widenand sensor and gauge take a look at how the spark plugs look.
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Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Porver9two4 · Joined: 22 Jan 2004 Posts: 104 Location: United Kingdom

Andy, you don't need to bother with a smoke test - you have already established that the injector seals are leaking. Yes, leaking seals can cause horrible running issues - we were always changing them back in Mk1 Golf GTi days. It shouldn't make any difference to the way it runs by spraying fluid around the injectors. The fact it did shows the seals are leaking - replace them, they are cheap and easy (although probably rock hard on your car and may require Herculean effort to pull the injectors out).
Beyond that I assume you have verified the timing and all the marks? checked that the cam timing is right by aligning the dot on the back of the cam wheel with the pointer whilst at TDC? and checked the ignition timing is right by checking the mark on the flywheel through the window in the crankcase as per the book? Vacuum advance working?
I am sure you will have checked all those already and my bet is injector seals...
Once replaced you will need to get it on a gas analyser to check and / or adjust the mixture at the metering head as there is no way of getting it right without analysing the exhaust gases.
If it still runs like a pig after changing those you have to suspect the metering head. Everyone says you can't rebuild these and they need to be done professionally - its perfectly possible to DIY them if done carefully (certainly for a man of your abilities anyway). If it were me I would only crack it apart after having removed and cleaned the piston only, refitted it and found the symptoms were the same. Only after that would I delve deeper - usually a sticky piston is the culprit and that can be cleaned without taking the metering head apart.

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

I agree with morghen, the best way to set fuel mixture is with AFR gauge.

There is an alternative method that Rasta has noted, and I believe may be documented in the Haynes as well; on US-spec Lambda-equipped cars, you can use a dwell meter on the frequency valve to set mixture.

But before you do any of that, definitely identify all vac leaks. It would be worth setting up a vacuum gauge, even a temporary one. You should be pulling 17 Hg at idle, anything less indicates a leak somewhere. Don't assume that the injector leak you found is the only one. Check all of the large rubber and plastic boots, check all of the gasket-sealed interfaces on the intake / throttle body / head, and check all of the rubber and braided cloth lines (there are MANY of them) that connect to the intake.

It is a good idea to replace the injector INSERTS as well as the injector O-RINGS. To remove the injectors, use the proper removal tool...less than $10 online: http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=SCLSL83400&source=froogle&kw=SCLSL83400&gclid=CjwKEAjwkJfABRDnhbPlx6WI4ncSJADMQqxdKfP-vArYVbPIBsV649TPX_2EXz0Pc15cpVd3VTnQiBoCz8zw_wcB

Smoke testing can be rigged up using a variety of methods. While I have yet to build one myself, the method I will use if I ever get around to it will be to use one of the cheap party fog machines. Do a Google search, there are many examples documented on the internetz.
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erstwhile owner of just about every 924 variant ever made

Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Update.

I've checked everything I can and replaced all the injector seals and boots.

Ive been through the intake system front to back with a fine tooth comb and have checked the timing.

Everything is as it should be.

The car is not road legal so I can't measure the AFR yet, but the plugs look fine after a thorough warm up.

I've checked the idle speed screw valve and set it to warm idle at 1,000 rpm.

After all the work and especially after replacing the injector seals and boots, it now runs really smoothly - but.....

Cold start idle is 650 rpm and labouring against it's own cold friction.

I've double checked the cold start valve.

Here it is at 60 deg F.

Here it is after 5 mins under a hair dryer.

I put it in the refrigerator and after 15 mins the air gap was open about 50% more than in the first picture - all which points to it;s correct operation.

I've checked the hose going between the unit and the inlet manifold and also the short pipe from the unit to the inlet tract - both clear.

It runs so smoothly and nicely and responsively and the plugs are near text book perfect, there is clearly nothing fundamentally wrong with it's settings, but for some reason, the AAV simply isn't doing it's job.

I even tried pulling the hose between the AAV and the inlet manifold whilst it was running cold and it started to cough and splutter as it suddenly got too much air.

I'm utterly baffled why the AAV isn't having any effect on the cold idle speed whatsoever.

Just to clarify....

New plugs, wires, coil, dizzy cap, rotor arm, injector seals, injector boots, cleaned and spray pattern checked injectors, new in tank fuel pump, checked WUR, measured fuel pressure for system, cold and warm. Checked fuel flow rate, checked air leaks all through system, checked timing, checked plugs, fresh fuel, checked and adjusted idle speed screw and o-ring. Checked all hoses and joints.

Fires instantly from cold, but runs at 650 rpm until warm.

What the actual fcuk gives?

924RACR · Posted: Thu Nov 24, 2016 12:31 am Post subject:

Well, just to clarify, the AAV shouldn't cause a high idle, just get it to idle at normal speed when cold. But your results seem to indicate that it's not doing it's job, if it's idling at 650 cold.

Given your results - very good job on the thorough troubleshooting, BTW - it would seem to me that when you're setting the warm idle, the AAV is still open and bypassing air - though it would appear to be working properly based on your tests.

One thing I don't see covered - is it getting power and ground when running?

Since you can't drive, I wonder if the car may not quite be running long enough to fully close the AAV when you set warm idle, particularly if it's not properly powered.

While it will eventually warm up by contact with the intake to match engine temp, during the warm-up cycle it needs electrical power to properly match the engine temp - thermal conduction takes too long.

So that's my thought...
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Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Last Triumph · Joined: 17 Oct 2016 Posts: 123 Location: UK

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Hi Last Triumph,

I had a very similar issue, and found myself on an identical quest, and all those same things checked out OK....

BUT STILL...

..Ran like a PIG when cold, smooth when warm.

My answer: Valve clearances were adjusted wrongly. (too tight)

So you might just wanna double check those.

BTW. I've got an exhaust gas tester. Where in the UK are you? Maybe handy to update that in your sig.

Keep up the wood work, can't beat that feeling when you win that battle!

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*****1981 - 924 - Auto - London, UK******