mfi on rebuild refuses to idle

[svandamme]

hi folks

i got my engine running last week
wouldn't idle, and running rich

i managed to lean out the main enrichment
it sounds very good when revving but it still refuses to idle


so far , i determined that my electrics aren't all that
zero power to my shut off switch, so that's not helping

however, if i manually trigger the shut off solenoid
the engine just kills instantly
it still doesn't idle , even with my throttle fully closed


so far , i checked the control rod lenght
checked the air correction screws


couple of questions,

is an mfi engine supposed to idle, even with this shut off circuit out of operation, i mean , is this system required for running , or is it a fuel saving 'feature' ?

any ideas on how to troubleshoot this? the literature discusses most things like changing idle , or , when idling , check this and that.....but there's hardly any info on what to do when the engine refuses to idle at all...

is it possible for the idling enrichment to be to rich? could this kill the idle?

the way it goes out is pretty instant , if i go to zero throttle
it stops immidiately , and sometimes i hear a psshhhh puff from the engine...

i'de like to get this fixed asap , so i can finish the break in under load... while driving... bit difficult , since no idle is a pita at red lights and such... and i don't want to stand there waiting while continously blipping the throttle... really don't want to attract boneheads looking for a race on my break in runs

[svandamme]

bump

[CliffBrown]

Stijn

Disconnect the cold start valve on top of the fuel filter assembly after it's warmed-up. Or pull the fuel line from the valve when running to see if fuel is flowing after start.

It could cause the motor to run rich or flood out at idle.

[tobluforu]

I'm no expert, but I've been tinkering with my mfi for 14 years now. Shut off solenoid will not cause car to not idle. I do not have one and my car idles great. If your leaning the hell out of the main adjustment screw(behind Allen bolt) from what I have found the car will run great (to a certain extent) when revving but will not idle. How are the stacks-are they properly calibrated? Your either not getting enough gas or not getting enough air at idle, or it is something different all together. Is the pump timed by aligning the FE (oops) mark? Also, have you advanced timing to see if you can get it to idle?

[silverc4s]

Stijn asked:
is an mfi engine supposed to idle, even with this shut off circuit out of operation, i mean , is this system required for running , or is it a fuel saving 'feature' ?

Yes, it should idle as a purely mechanical system, even with the solenoid removed/diconnected.

I think that the switch/circuit is capable of completely shutting off fuel pump - perhaps it is shorting or broken?

It sounds like you are getting NO fuel at idle for some reason - perhaps initial settings on pump? Was the pump freshly overhauled?

A new engine is pretty tight, so it would need MORE energy to idle than a run-in equivalent one.

Wish that I could be more help, I assume you are using the CMA procedures..keep us up to date.

Good luck

[svandamme]

Cliff : the cold start injectors are allready disconnected ( had some major flooding last year because of those puppies )

tobluforu : i leaned it as far as possible, untill it started to pop
then enriched it a little till it ran smooth again
it didn't idle before or after i started adjusting mixture

the pump alignment.. could this cause non idling?
must admit , i had set dizzie and pump correct prior to starting it
but my dizzy was wrong... and haven't looked back at the pump after it started running .... i'll check it first thing in the morning when i go back to the garage

bill : there's no power on the solenoid at this point
my cars electrics are quite tired... i'll first go for mechanical functionality ... especially if it should work without them.

[Early_S_Man]

Stijn,

The Cut-off Solenoid is strictly a fuel-saving system [1-Speed Switch, 2-Microswitch & 3-Cut-off Solenoid] to be utilized above 1500 rpm or so. It has no effect on idle ... unless there is a fault in the system or wiring! Disconnect the Cut-off Solenoid and tape up the connector on the wire until you discover the problem causing the non-idle situation!

It sounds as though you have been skipping around in the CMA procedures. Go back to page 10 ... Step 4 - check/set Dwell Angle by putting a meter across the points ... one lead to Black/Violet & Black wire at distributor and other lead to ground. Then, reset timing - Step 5, and proceed through the rest of the sequence in order.

Injection pump timing is set at the FE mark on the crank pulley, not Z1 -- the FE point is 40° After TDC! This [pump timing] would not cause a no idle situation , but it could cause a 'roughness' quality to throttle response.

What is the lowest engine speed attainable by setting the hand throttle, currently?

[304065]

Stijn,

So when you have air flowing through the throttle plates, when your foot is on the gas, it idles. But when you close the thottle plates all the way, the engine stops.

That to me sounds like you are suffocating the engine due to lack of air. Did you recently have the throttle bodies rebuilt? They must be pretty tight to not pass ANY air at all. In any event, start by closing the airbleed screws on the stacks, then open them five half-turns, and try that. I would NOT monkey with the thottle plate angles yet-- the air corrector screws are easy enough to put back. If that helps, then get out the synchrometer and synchronize all the stacks to the average.

I echo the sentiments of our friend from San Angelo: I would do a systematic step through CMA so you know you aren't missing anything.

Good luck and congrats (in advance!)

[svandamme]

hi Warren , i did go for the FE mark on #4 TDC
but i'll recheck this just to be sure

lowest speed, around 1200 rpm , but no hand throttle
that plastic thingie don't work on mine. allready replaced it , but no go

i need to keep revving or it stalls, currently i used a tie rip on the linkage to sort of keep it going while i troubleshoot

John, did not rebuild my pump nor did my throttle bodies get rebuilt.... budget constraints...

i did unscrew all the air screws, one by one, cleaned them
and then fully screwed in , 5 turns out .. like in the adjusting mfi by Lee Rice... no noticable difference, then i did 4 more turns out
still nothing... that's when i paused, and left for the day , to consult tha board

[Zeke]

It's been a while since I put myself to sleep reading the CMA. I'd like to get to the point that I have it memorized. Anyway, IIRC, part of the procedure is to adjust the butterflys and then trim the flow out with the air screws. By starting with the air screws turned out five HALF turns, you give yourself a little margin to go either way while trimming the individual stacks. If there is not enough air passing the throttle plates, the screws won't provide the full volume that is needed.

There is another reason that the throttle plates need to pass air and that is so they are ever so slightly open when they are on the stops. This keeps them from closing completely and sticking which they can do under certain conditions. And, completely closed would seem to me to cause undue wear on the throttle body bores themselves. Slightly open and they don't touch the sides of the bores.

After setting the timing and making sure the valves are adjusted correctly, start with warming the car up and disconnecting all the linkages. Then set the individual butterflys (sorry, I'm using 2 terms for the same thing) so that you have close to correct idle speed and they are equal in flow according to a flow meter. You may have to adjust mixture to get things to smooth out and this could cause the RPM to change. Then, you have to go back thru and do it all again until everything is right. Only then, can you connect the linkage, which is another job in itself, getting all the throttles to come off their stops at the same time.

This is only an overview of some of the procedures you will perform to ge the system to behave. If your shafts and linkages are worn like mine, you will have a hell of a time finding compromises that are not in the book. One more thing: the cut off switch can exert enough pressure to cause the linkage to not come to full rest. You have yours disconnected, but is it removed or adjusted way down? I want the thing to work because it prevents backfiring, but you don't want to do all this work and find your springs are strong enough to hold your linkage closed at idle, expecially as you dial out vibrations and roughness tha surely throws the thing off. Use an extra spring here and there while working if in doubt.

I could have some of this wrong, it's all from memory and as I said, I don't ahve the CMA memorized yet.