Late FI Notchback running problems

[packers1712]

Hi everyone, foolishly today I attempted to cure my "part throttle rough running" issue, I have systematically tested the entire FI loom and components trying to find a cause of a rich mixture and high hydrocarbons but everything has tested OK, so just in case it was a dribbling 5th injector I have disconnected the fuel feed to it ,refitted everything and now it will barely even idle, it pops and bangs when I try to rev it ,what could have disturbed to cause this?
Any help greatly appreciated.

[Editor]

Check all the plugs and earth connections are firmly in place. Most likely you've disturbed one of those. The CHT sensor has a clear plastic connector that rests on the engine tin - I knocked that when dusting the engine once, and it wouldn't start! (BTW, did you check the charging volts were OK? I can't remember if you already replied, but that could be a reason for the high HC/rich mixture if not).

[packers1712]

Yeah thanks Dave, I have had that CHT connector apart and found that it won't run with out it connected,I had an issue with it running when i first bought it that you diagnosed for me, not charging at a high enough rate, I must admit i haven't checked that this time but I will. I think it must be a connector issue of some sorts, I started the engine after every check that i did, it appeared to run no different from before I started my diagnosing, and when all of the components tested ok I decided to refit everything and call it a day, tried to restart the engine one last time and found that it runs worse than ever, wished I 'd left well alone.Just one thing on the rich mixture, my car doesn't have an adjustable ECU so with all the components testing ok how do I lean it off? I asked the MOT tester to check the emissions for me and the CO was at 5.3% and the hydrocarbons up at 3000ppm's!

[packers1712]

Just been trawling the web and found a good point that maybe when I was down on the top of the injectors blanking off the coldstart injector maybe I've disturbed the Injector "O" rings when i was down there!

[Editor]

Those emissions figures are way too high for FI. Even my twin carbed manages about 3% CO. I found the FI Fastback was around 0.5%, according to the DIY-quality gastester.

You're right, there isn't any adjustment. It's all factory set. Sometimes mechanics dig out the epoxy from the end of the Manifold Pressure Sensor in the hope they can improve things by adjusting the screw, but there are two concentric screws and adjusting one can move the other,making it a lottery to get it back in the correct position.

The CHT sensor itself is the only mechanism for enrichment when running - check it hasn't gone open circuit, or shorted to the casing; open makes it rich, and shorted makes it lean.

I think one of the MPS versions can break its internal diaphragm. Try an email to Jim Adney, jadney@vwtype3.org . He's a good friend in Wisconsin who is an expert in Type 3 FI, and may recognise the symptoms. He did join this forum some years ago, but is rarely on. We last met a few weeks ago in Arizona for the USA Type 3 meeting.

[packers1712]

Had another play last night, re-visited everything again and didn't find anything, temp sensor 1 (CHT) tested good when cold and hot so I have to believe its working correctly, did find an air leak on the pipe to the pressure sensor, so sorted that and the idle is much better now, I do admit I did have a play with the adjustment screw in the end of the pressure sensor with some success, no black smoke when I rev the engine and the idle is much more stable I just need to get the emissions rechecked to make sure it isn't too lean at fast idle.
Thanks again Dave for the advice, I'll see how it drives down the road and like I said get the CO checked and go from there, if i need more advice maybe I'll contact your friend in the States.

[Editor]

I think the car has probably taken the chance to give you a rap on the knuckles!.

If you didn't have to remove the epoxy resin plug from the MPS, a previous owner has probably adjusted it wrong. I did tweak my '72 as it was hunting, but then had to move it back again some months later when I found it was over rich again - not sure what corrected itself meanwhile.

[packers1712]

Just a quick update on the my notch, it's running well now ,not perfect, but i think I'll have to live with it. After visiting the garage to re- check the emissions, CO 3% but HC still up at 3000ppm, I think I may try a plug change in an attempt to clean up the HC's but for the most part I'm going to leave it alone all the time its running well.

[Editor]

Are the compressions reading oK? That was always a standard item on the VW servicing - used to get a little card showing how they were!

[packers1712]

Yes they're all good, I had another issue a little while ago where it wouldn't start when it was hot and after further investigation found no valve clearance on cyl number 3 and tight clearances on number 2, reset them all and compression tested, 130psi on all 4 and hot start issue all sorted.

[Editor]

Fuel pressure 28-30psi? Air cleaner cleaned recently? Puzzling!

[packers1712]

Fuel pressure is 28psi but I have to admit its been a while since I've changed the oil in the air cleaner, it doesn't look particularly dirty!

[Editor]

We get a fair bit of rain, so don't suffer from dust very much - I've rarely changed that oil in mine. Maybe every 3 or 4 oil changes, if that often.

[packers1712]

Hi everyone,

Just revisiting the running issues with my FI notch, over the winter i had the throttle switch refurbished in an attempt to cure the slow engine speed, driving in traffic, very light throttle opening "jolting" almost like a misfire. Initially I was confident the refurb had cured the issue but driving it the other day proved that it still has the same symptom. I have messaged the chap that did the refurb to see if he had any tips and he mentioned the problems associated with the pulse generating points, i have had to repair mine and can't find any new ones for less than £200, what I'm getting at is is it likely that repaired pulse generator points (regapped due to worn cam heels) will give the driving symptoms that I'm experiencing? Is it possible to have smooth running with repaired points or do i need to replace them with new? I have removed the injectors this evening and will ultrasonic clean them but not that confident they are causing my issues! Timing is checked and good, no air leaks, fuel pressure good, charging rate good, there is some play laterally on the throttle butterfly and the return spring appears to have plenty of return tension to it.
Any ideas greatly appreciated and any info where to buy new pulse generator points for less than a small mortgage also welcome.

Thanks in advance, Doug.