411 D Jet CHT question..

[Dubs]

Hi folks.

Apologies for making my first post a question

I have been lurking around for some time reading the excellent info on here while re comissioning a 411 variant that had been dead for some time...and I am pleased to say that its actually running pretty good now, with the exception of a mildly annoying cold running issue..

The problem arises after about a minute after starting from cold..initially it idles dead steady, but then the idle starts to rise and fall slightly (about +/- 100 rpm), and has a flat spot / hesitation of idle...its fine at higher revs and evens out once the engine is up to temperature. Its slightly improved now I have disconnected the air intake temp sensor but is still there...it sounds to me like its a tad weak while its warming up..

On testing the resistance of the CHT I get a reading of about 1800 ohms before startup, temp in my workshop at the time was -1c. once the engine was up to temp and the thermostat fully open it was reading 90 ohms. Are these readings about right or is the CHT duff? and if it is duff, are new ones, or alternative ones, available? I am sure I read somewhere that the cold reading should be much higher than 1800 but cant find the figures now..

Any help much appreciated folks

[Piledriver]

Welcome to the asylum!

As to questions---we all have them, that's why we are all here.

I'll have to dig out the books on that as far as specs, but hopefully Ray or such will chime i before i get home from work.

[Dubs]

Cheers Piledriver

This is my first venture into the world of D Jet FI so I imagine many more dumb questions will follow..

[raygreenwood]

90 is a bit low for cold weather warmed up. I would expect about 150 ohms at that temp. typcially with age these sensors die. They are about $30 and available.

The problem you are dealing with is a slightly rich or lean baseline fuel mixture. Get your CHT replaced, check your fuel pressure and make sure its stable at 28-30 psi.....and carefully adjust your valves, set your timing and clean and oil all parts in teh distributor.

Then carefully clean every connector in the system. One dirtly or slightly loose connectpor means resistance. Resistance means fuel mixture change.

Make sure you have no vacuum leaks and that your AAR is closing smoothly. Check back and we can go from there. Ray

[Dubs]

Cheers for the help Ray, much appreciated.

I have ordered a new CHT this morning.

fuel pressure is now bang on 28 psi with no fluctuations now I have fitted a new pump.

the dissy that was on The car turned out to be a type 3 item according to the part number and has been replaced with a correct item that I cleaned and lubed up...I Had to swap the vac can for the type3 one though as the type 4 one was unserviceable. I assume they are the same...

as the car came to me as a non runner, and had been standing for some years, all vac pipes, fuel lines, seals and gaskets have been replaced. I am 99 percent sure that all air leaks have been eradicated...

the AAR had been disconneted when I got the car...on checking it I discovered it was not opening so I dismantled it and freed it of. it now works in that its open when cold and shut when hot, I haven't actually timed how long it takes to open but I would say about ten mins.

I did check the valves when I got the car. although I will double check they are absolutely spot on before I go any further.

electrical connections is a good call, I hadn't thought about poor connections causing resistance... I will give everything a good clean up and report back.

Cheers again for your input.

[Piledriver]

It's best to entirely ditch the .250" push-on ground spade connector setup and replace with properly crimped on loop-type connectors under the same nuts/washers.

The hot melt glue sealed type are greatly preferred fo obvious reasons.

A good ratcheting crimper will last a lifetime, and pay for itself in a hour or two.

[Dubs]

Happy days...The CHT sender turned up today so I fitted it up and there was an immediate improvement...the idle has stabilized and risen noticeably...with the idle speed re set its running really well now, much more responsive when the throttle is blipped as well.

I am going to renew all the earths as well for peace of mind as they do look a bit tired to say the least..

Sadly, with this problem fixed, another one presented itself as soon as I moved the car ...a leaking gearbox! but thats for another thread..

Thanks again for everyones help