A warm engine running issue

[oscar]

The only thing is my 350 has no EGR.  It's a pretty featureless engine when it comes to emissions and I've always put it down to being an early model.  But maybe the idle retard was the only step they made.  I need to make this advance unit my next purchase I think but like koan suggests, the retard shouldn't affect driving, even though I felt like it did. Whatever was going on it didn't cure the issue completely but it did help.


BTW, I plumbed the advance of the 280S into the holley carb instead of the plenum.   Made a big difference.  It's parked on a slope.  If I try and reverse too soon it'd die.  Now, only needed a minute or so to warm before I could move the car without hessitation.  Just need to do timing again and check fuel mix properly and give it another burl.

Quote oscar

Notice they say retard becomes effective when the AC is switched off.  Logic and from what you say about idle stabilisation would make one think the opposite.

The opposite of that is no retard with A/C on which sounds right to me.

Showing my tru colours.  Another blonde moment.  It all sounds right to me too.  I was up reading late, jotted some details down, did some head scratching and wrote the post in the morning.  It made sense at the time.

Re the US distributor that looks like it can only retard, I'm sure styria's w108 3.5L dizzy pulled rather than pushed the baseplate when I sucked on the port, which in my mind had me thinking it could only retard the ignition.  That's why I believed I couldn't use it.  And all those dozen or so diagrams have the retard line that comes from below the throttle plate going to the outside of a single can or the nearside to the dizzy for a dual can.

[oscar]

Ok, I've had another look and for the first time I think I've managed to time my engine properly (almost). ie vac lines were disconnected on a warm engine, factory timing mark used (I often turn the dizzy till I hear no pinging when engine under load then use a timing light to see where I ended up), rpm set at 750approx.  The result is things aren't right and all this time I've used the warm idle air screw and advanced timing to counteract a dodgy air slide, ruptured advance diaphragm and whatever else is making the engine lag. 

Once fully warmed up, I left the vac retard off and plugged as it made the situation worse at idle.  My vac advance being cactus I left that off too.  What happens is the idle develops a sine wave pattern between low and higher revs.  Nothing wildly high, something between 650 and 750 rpm perhaps every 1-2 seconds.  A slight touch of the accelerator with the throttle plate just beginning to move will cause misfiring and if sustained in that position, sometimes would stall.  Rev the engine and it seems to run fine but on the overrun as injectors stop, it sometimes doesn't recover to the idle and will stall as the injectors kick in again.

Any more ideas?

Firstly, I need help with the thermotime switch.  I know 2 is the coolant temp.  What's 1 and 3 and how do I test the thermotime switch if 1 or 3 is it?  The manual isn't making much sense to me.  I also disconnected the cold start valve whilst warm in case it was flooding but it had no effect.

[oscar]

I've found out that 1 is the thermotime switch, but I've still no idea what 3 is.  Anyone?

Something else I did today was adjust the Throttle Position Sensor.  I popped the cap off, inspected the contacts and adjusted it back and forth and couldn't make the boggy transition from idle to part throttle any better.  In fact, it got worse.  Several times I got the switch to make the  20 "click" noises with ignition on, engine not running.  The clicks didn't occur on returning from a full throttle to idle.  That's how it's supposed to be.  So to my mind, this plus the continuity and terminal checks I did before makes me think everything is fine with the TPS.

However, I disconnected the lead to the TPS and went for a drive and the problem basically disappeared.  This would point to a faulty TPS despite my tests to the contrary.  

What are the consequences of running the car without the TPS connected?

[koan]

The loping idle sounds a bit odd oscar, only times I've heard it before is on done over engines with big cams. Maybe the injection system is doing something odd.

A new advance unit without a leak might help.

The TPS is more than a position sensor, doesn't it have a separate closed throttle switch? Despite your wiring and continuity tests the fact that it runs better without it connected suggests something is wrong there.

koan

[oscar]

Yeah, the TPS has a switch for an idle circuit which is fine I believe.  The ECU runs a separate calculation for idle and it's adjusted by the CO screw on the ECU.  The TPS also contains the fuel shut off switch for cutting off fuel during overrun within a certain rpm range.  It also has an "accelerator pump" effect to counteract lag of the manifold pressure sensor and others.  This would be it's main purpose and without it, there didn't seem to be too much difference.  Well I suppose because it accelerates properly it feels better.

More testing today.

[oscar]

Fixed it

It was the TPS after all.

Basically it has two moving parts.  A switch and three wipes. The switch is black plastic and moves first when acceleration occurs.  the brown plastic soon follows.  The problem is the common hub that the plastic rotates on needed lubricating.  I also think the reed like contacts of the switch had lost their springiness somewhat.  Slight movement of the throttle would cause the two plastic parts to bind a little and the switch which I believe needs a clean and immediate switchover between contacts, would find itself in no-man's land, thus causing the hesitation, or so me thinks. 

The fix was to lubricate the hub a little and carefully respring the reed contacts


From idle to initial acceleration, with no movement of the three wipes, the switch moves first causing the contact with the right pin.  Lubrication of the hub seems to have fixed the binding between both black and brown plastic parts allowing independant movement during that intial touch of the acclerator.



Next the wipes move.



Lastly. The embarrassing part.  I had to go too far didn't I.  Maybe the reeds didn't need restensioning after all.   I snapped one of the reed contacts whilst reshaping them .  I've soldered the end on and and built a bit of solder up then trimmed some away after the photo was taken.  In the future I'll get some phosphor bronze wire or similar and attach a more permanent solution but for the moment, I reset the TPS and still got the 20 clicks for acceleration only which is correct.  The switch movement is intially independant as it should be and despite the ugly solder job, there is a very quick switch from the left to right pin and vice versa.  Just been on a 50km round trip with a lot of slow starts. 
All's good. No hesitation whatsoever. For the moment problem solvered.

[SELfor50]

Nice work mate!!

You're a deadset inspiration - these are the things i wanna learn bout my engine, and i have to thankyou for doing the hard yards!!  In good time, i'll be checking all these things on ol' silver.

Drop us an update on how she runs over the next couple hundred km's.

[koan]

Good one oscar, interesting to see how the TPS works.

Regarding:

    "The embarrassing part.  I had to go too far didn't I."

I know all about that, done it for years, you know how it happens. Feeling a bit pleased about fixing something that is not supposed to be fixable, I'll just do this last thing on it that doesn't really need anything more doing... too late, it's stuffed.

I think I'm finally at the stage where I know when to stop, taken a few years to get there though.

koan

[s class]

    "The embarrassing part.  I had to go too far didn't I."

There are lots of forms of this misery - like completing the assembly of something and reflecting if everything is tight enough - 'I'll just give that one bolt there a little bit extra' - you know that's whe something strips......

[oscar]

I just wish I did all my "learning from mistakes" on another car and kept this one as my work of art.  If anything it's won top marks as a survivor considering the mistakes and experiments I perform on it.   But I love how it's got parts that can be fixed rather than requiring replacements.

selfor50 - I'm not sure your post '75 450's have a TPS.  I really don't know enough about k-jet to know if it has an equivalent or not or whether it's the same.

[s class]

K-jet has no TPS - its ALL MECHANICAL. 

Oscar I think working on cars is a learning curve that never really flattens out. 

[SELfor50]

Thanks Oscar - guess it's not that, i'm assuming it is something to do with the lifters or valve seals / guides etc.

When my girl is warm too, if you rev her a bit then let go she almost sounds like she's bout to stall...thought it might be the same thing
but yeah i don't have a TPS which cancels that thought.

And same as yours, it's only when it's warm - i thought it was the cold start injector but even after disconnecting that it's still doing it.  Not that badly mind you, just one of those niggly things.

Any other suggestions?