Ignition fault or vacuum?

[purplepeter]

Start with the simplest thing- When did you last change the fuel filter?

[Rob 400e]

Changed the filter about 650 miles ago (three months) with the stock square one. But I’m guessing your going to suggest start at the filter and work back to the engine bay which seems logical. Could be a faulty filter? I will work through to the injectors and let people know if I find anything.

[richtbiscuits]

You say it's running rich and the plugs are black. Have you cleaned or replaced the plugs? A poor spark is sure to cause a poor burn and rough running. Also, do you have a control knob on the ECU? Not all do but if you do I think its anti-clockwise for lean and clockwise for rich. Good luck with the fault finding - it's not type 4 ownership if you're not chasing some niggle with your FI!

[937carrera]

You say it's running rich and the plugs are black. Have you cleaned or replaced the plugs? A poor spark is sure to cause a poor burn and rough running. Also, do you have a control knob on the ECU? Not all do but if you do I think its anti-clockwise for lean and clockwise for rich. Good luck with the fault finding - it's not type 4 ownership if you're not chasing some niggle with your FI!

He's got a fundamental problem with the temperature sensors. and possibly the auxiliary air valve Until those are sorted further changes are simply likely to make proper diagnosis and an ultimate fix more difficult .

[Rob 400e]

So on initial cold start the engine runs smoothly at about 1100rpm for about two or three minutes then drops To 850rpm. I’m assuming the cold start is working ok. When the engine reaches working temp the problem begins.
I can rev the engine hard with no misfire but when the engine is idling it starts missing but blip the accelerator and it picks up immediately.
All the pipe work is new and on tight (vacuum,air) the bogging down is more noticeable when drive is engaged to the point of stalling. But it will accelerate with no issue.

[Rob 400e]

I have taken the plugs out checked the gaps and wire brushed them, also checked the valve clearances again all good. The points gap is o.4 mm. it’s ran well in the past with the central thermal switch disconnected, so can’t see how that would suddenly become an issue. It’s a puzzle. I’m thinking more and more it’s a sticking injector, would that be not so noticeable at speed but more so on tick over??

[broady_6]

If you had a stuck injector then I'd expect to see a plug with very black or very light grey. What were they like? Have you done a compression test?

To me it sounds more like an air leak. They're usually more noticeable and idle speeds and at higher load they're well masked by the extra fuel.

[Rob 400e]

The plugs were jet black bordering on sooty. Why would an air leak make it run rough on idle but have no effect when driving? How could I test for a leak?

[broady_6]

Air will take the esiest path. So with the throttle butterfly closed you place a restriction in the intake. So if there is a hole else where air will leak in there. This will mess up the Air Fuel Ratio as it is unmetered air so the ECU doesnt know about it. At full or much higher throttle the butterfly is much wider open. So less od a restriction, more air will flow in that way compared to the leak. More metered air, means you are closer to the correct AFR, making the leak less noticable. You could test with a squirt of WD40 or similar at all the joints on the intake system. if you get a sudden rise in revs then youve have found the leak.

[Rob 400e]

Cheers for that will give it a try, fingers crossed it may be a cheap and easy fix. I will give it a go in a bit and keep you posted.

[Rob 400e]

This is a strange one, tried Broady method to check for air leaks nothing of significance so striped out all the bits to do with air intake. Cleaned everything checked all pipes for damage all was good. While everything was stripped out I decided to check the plugs again bearing in mind I had wire brushed them and re gaped them yesterday and found soot on plugs 1/2/4 number three was as I had put it in the other day. Logically 3 is miss firing,put it all back together tried the pull the leads off one at a time and number three no play. I put a spare plug in number 3 lead and put it to the crank and it’s sparking no issues! So I had a look at Henry Elfrink FI manual and on page 63 found this “erratic idling type 4 models” basically it tells you to re route the main wiring harness away from number three plug lead I cable tied the harness to the intake manifold and re routed the plug lead over the top and bingo back to smooth running it looks a bit odd but eh!
“Intruding inductive effects of the high tension ignition system” who would of thought.

[Rob 400e]

You will appreciate this is a temporary fix at the moment I have a wiring harness cable tied to one part of the air intake manifold and a fuel line cable tied to the other side. In effect I’m driving a mobile bomb with a smile on my face Don’t try this at home!!

[broady_6]

FIngers crossed it proves to be a fruitful fix then!

[Rob 400e]

Yes, fingers are crossed. Will fire it up later just to convince myself. All being well I will tidy things up cheers all.

[Rob 400e]

I guess social distancing applies to your wiring harness as well.

[broady_6]

I do wish they could sort out their terminalolgy. its "physical distancing". I am as anit social as I have ever been. but i do now stand further away from people. Its like global warming, if they got the name right to begin with it would have help. global warming sounds quite nice. Id be pretty happy if it was a little bit warmer, its always too cold in this country. While my tounge is in my cheek, its certainly not pressed there hard!

[Rob 400e]

Well fired it up went for a spin and it’s still missing occasionally on tickover. It’s not journey stopping but it’s really annoying, I’m now not that convinced about the harness deal, or it could of been a combination of issues. Still clueless.

[937carrera]

You have two problems:

One cylinder not running properly (3 plugs sooty, one unchanged "number three was as I had put it in the other day"), as it's sparking then it's the fuel that's not there, probably an injector problem, possibly wiring to the injector..

Running rich by default, because not all the sensors are connected / working properly, and possibly someone has done something to compensate for these errors

The bogging down at slow speeds is because the mixture is too rich. I very much doubt it is an air leak, because if it was you would have unmetered air, so fuel would be delivered to meet the (reduced) demand called for by the MAP sensor etc

I expect the problem is reduced when the engine is cold

Does that make sense ?

[Rob 400e]

Hi, to be honest the car is 95% improved as a result of moving the harness. Have you heard of that problem and cure before? I thought it was a wind up. To be given a paragraph in a manual such as that it must be common on my model.
Anyway back to the job in hand it runs with no issues on cold start up, it’s missing occasionally when warm. If it was the signal to the injector it’s very intermittent. I could not detect any air leak with Broadys method. I don’t have a rev counter but think it’s running a bit slower than it should I will speed it up a little. According to the Haynes manual the throttle should be set slightly open mine isn’t. I’m not giving up yet.

[937carrera]

I think I had heard of the wiring harness problem before, but it was deep and buried away.

You have confirmed that the problem is gone on cold start. For me that's a further confirmation of basis rich running., You need a richer mixture when cold, you're just running a rich richer mixture, and it'll take it. When warmed up and being closer to stoichometric is more important the misfire returns. After a run on the dual carriageway the engine will be hotter so the problem is potentially exaggerated. That and the sooty plugs of course.

The idle speed is set by the bypass screw. that's the pimary adjustment. Because yours is an auto there's also a vacuum operated adjustment. Just like with the rest of the sytems, get the primary adjustment correct, rather than try and achieve it through a secondary method . I didn't know about the auto extra bit until I looked on page 68.

Ask yourself one question...... why were 3 plugs sooty and one not ?

[Rob 400e]

Ok, will answer the sooty plugs problem first. The intruding inductive problem only effects cylinder number three because of its close proximity to the harness hence that cylinder wasn’t firing as regular. I’m guessing if I check it tomorrow it will be sooty. I want to get the idle RPM sorted tomorrow and the throttle vacuum and see if that effects anything, don’t suppose it will. Now it’s running reasonably well I can move forward with the rich running infact I will connect the temp sensor and see if the hunting has stopped. Look at number three plug as well. Cheers

[packers1712]

Wow guys seems like you've covered quite a lot of ground since the last time I looked, I've never heard of the "intruding inductive" issue before sounds plausible though, hope the investigation keeps turning up valid causes of faults.
Good luck, I given up with my Type 3 and am ditching the FI in favour of carbs - fed up with spending more time chasing faults/issues than driving it!

Doug.

[Rob 400e]

Know where your coming from, it’s just one thing after another I’m struggling. Would convert to carbs myself but determined to keep it as stock as possible. At what cost , my sanity!

[Rob 400e]

Latest update.... decided to check out the injector on cylinder 3, firstly the electrical connection pops in and out a bit to easy for my liking changed the injector for a known good one and re assembled. Pushed on the connector and put a small cable tie around the connector for the time being. Fired it up ran ok went for a quick spin now I have a wheel wobble!! Unconnected obviously this car hates me.

[sparkywig]

Just persevere, mine is the same. You just need to start on one issue and get that fully sorted before starting on another.