D-jet idle and lean issues. Options

[Ishley]

If it was stuck closed then it wasn’t contributing to a lean condition. But glad it works now… if your pulling more then 17 it will open at idle which you don’t want. So you may need to adjust it more.

[Literati914]

If it was stuck closed then it wasn’t contributing to a lean condition. ..

Would stuck closed contribute to a rich mixture? - that's what I think I'm dealing with ..

[emerygt350]

No, on djet leaks or the lack of doesn't affect the afr. The vacuum signal reaching the mps will and the cht/charge temp sensor/ ECU pot at idle (not sure you have that, 72 is an odd year) are about it for mixture.

Sticky injectors but I believe you just rebuilt the motor so I suspect that isn't it. Once you get that afr working hopefully we will see if a rich idle is the issue.

Did you check to see if your mps was holding vacuum?

[Ishley]

The valve works (when adjusted properly) as a fresh air bleed when your driving along and let off the accelerator. The rapid jump in vacuum (engine spinning high and a closed throttle valve) opens this air bleed circuit. The technology at the time couldn’t shut the fuel off quickly enough… which caused a temporary overly rich situation. The extra air introduced, along with the fuel allowed the engine to burn the mixture while the engine was spinning down. This solved backfire issues and lowered emissions.

So yes it does solve rich issues but only in the few seconds while the engine is spinning down. Once the rpm and vacuum are lowered the valves closes/ extra air is cutoff…and normal operations resume. So probably not the issue… but it will help some.

Others may have more to offer here… but this is the way I understand the operation.

[Ishley]

Yes MPS check for sure. I’d also check the injectors. I’ve had issues with injectors that are new… and only have 5k miles in them.

What I did… take both injectors out on one side… and set a small tray underneath. Disconnect the coil.. you don’t want anything sparking. Get a helper to crank the engine while you watch the spray pattern. You should be able to get a good reading in just a few seconds. I had one that was more of a squirt than a spray… I replaced it and it fixed a lot of issues. Not really a full technical review of the functioning of the injectors… but a quick and dirty way to spot problems… and really not that much work.

Good luck!

[Literati914]

..
Did you check to see if your mps was holding vacuum?

Checked it, yes holding vacuum. takes about 5min 15secs to go from 20inHg to 15inHg vac - so within the parameters at least, as mentioned on Brad's pages.

[emerygt350]

..
Did you check to see if your mps was holding vacuum?

Checked it, yes holding vacuum. takes about 5min 15secs to go from 20inHg to 15inHg vac - so within the parameters at least, as mentioned on Brad's pages.

Great. I bet it's just a rich mix. Now on to the afr....

[Literati914]

Ok I'm back to trying to get my 1.7L W/ D-jet as correct as possible..

The Good News - adding a 250mA fuse at the heater input of my Lambda processor got it working instantly (IMG:style_emoticons/default/piratenanner.gif) . The gauge settles in at around 15.8 -/+ after a good warm up period... but now that I've put everything back together I'm idleing around 1700rpm (up from 1100rpm before diving into this), it never changes from start to about 10 minutes in when I've just decided to shut it off..

15.8 @ 1700 idle. Screw on TB is closed. Knob on ECU makes no difference.

So basically I've un-stuck the AAR and adjusted/un-stuck the Decel valve.

Maybe I still have the decel valve misadjusted and it's opening earlier than it should - would the open valve / extra air contribute to the increased idle?
Can your level of vacuum at idle be determined with just a simple hand-pump vac. gauge?

TPS circuit board is on the way but I'm trying to find anything else.

[Ishley]

Pull the hose off the decel valve and plug the end. Does the idle come
Down? If so your valve is opening at idle and needs to be adjusted. Also, push the throttle valve by hand back to idle. Does it slow down? If so your throttle body might need a rebuild.

[rjames]

Something else to check: If the distributor has the vacuum canister for retard at idle, is the line to it from the TB connected, and is the canister functioning correctly? If not, that will cause a high idle or for it to surge, depending on its condition.

[emerygt350]

Yes. You can use your mighty vac to measure vacuum. That line to the decel (the small line) works great for that.

Just methodically plug all vacuum sources on the plenum. 1700 is about a quarter inch hole so it could be any of them. I would start with the pcv.

Pot on the ECU won't work if the car doesn't know you are at throttle closed. Also, at 1700 I bet the pot won't matter anyway.

After you check all the hoses we can poke at the timing. Original distributor right? Retard and advance?

[Literati914]

Pull the hose off the decel valve and plug the end. Does the idle come
Down? If so your valve is opening at idle and needs to be adjusted. ..

BINGO - the idle dropped when I pulled the hose off the small end and covered it with my thumb.. 1700 to around 1000rpm. Guess I need to futz with the decel valve some more.

I hooked up the mightyvac to the small hose coming from the plenum, while idleing - the engine turning around 1000rpm -/+ in this condition ... and I seem to be pulling around 17-18inHg. So I'll try to adjust the Decel valve a little past that.

[rjames]

(IMG:style_emoticons/default/aktion035.gif) (IMG:style_emoticons/default/beer.gif)

[Ishley]

Did the Air fuel ratio fall once the idle dropped?

[Literati914]

Well blocking the small hose from the plenum with my thumb brought idle down to 1000rpm apprx (still not the suggested 850)… but, I adjusted the decel valve to apprx 19inHg and that sets my idle to about 1200rpm (after a good drive and warm up). I still occasionally got some backfiring if loading up the cylinders with fuel and not using all of it before/while decelerating. Also, while driving the gauge tends toward too lean (inexperienced opinion I guess, but I’d regularly see 17,18,19s).

Here’s a shot just after the latest test drive, back at idle:

[emerygt350]

That is looking really good. Until you get the TPS fixed I wouldn't worry about anything. You will be chasing your tail till all the bits are functional. Set that decel to 20. My car pulls 23 till it warms up. After it is nice and hot it does 18-19 at idle.

Do you have your original dizzy and is it hooked up correctly?

[Literati914]

..Do you have your original dizzy and is it hooked up correctly?

I believe the distributor to be original yes, it is the correct model for this car and components - I remember checking not long ago. It no longer has orig. points, has an electronic magnet based insert. Seems to work well enough from a casual perspective. The vacuum canister is present and hooked to the TB correctly I believe.

About my Decel Valve - I believe it needs to be replaced. I glazed over the follwing description until now:
" Leaky vacuum chamber: If the diaphragm is cracked, the control part won't hold a vacuum and will leak. Pull a vacuum on the control port, if it bleeds off rapidly (1-2 seconds), the valve is defective and must be replaced."
Mine (set to open at 19) goes from 15inHg to 0 in about 20 seconds.. but will not hold. Pbanders is kinda vague with the 1-2 sec thing, 'cause maybe that was at 5inHg pulled, or whatever.

[emerygt350]

Yep, that's not good. For the time being just plug off that line. Many guys used to delete the decel so the engine would rev down more aggressively. Not good for the longevity of your mps diaphragm though.

Verify your retard and advance locations. Retard goes to the back of the TB, advance to the front.

Advance is on the outside of the can pointing away from the dizzy, retard is pointing towards the dizzy on the inside of the can.