Rich stumbles? <SOLVED

[cygnusx1]

OK I have spent a few weeks sorting the install of the TO4B and the Spearco. I got rid of all the bugs except for this one. If I accelerate about mid throttle and hold it where it slowly builds boost with moderate load and acceleration it will build to about 7-9 psi and then stumble like mad and throw black smoke puffs out the back. If I then push the pedal harder, it will clearup in about 2 seconds and build boost to 13 and go like heck with no visible smoke. It idles very clean as I confirmed on a tailpipe sniffer and the plugs look pretty clean if not just a bit sooty around the outsides. The TPS is working perfectly, the temp sensors are working and I have the Pop-off valve tie-wrapped. Plugs are new NGK at 0.030" gap, timing is factory spec for '83 turbo and the fuel pressure is factory spec. I just confirmed all of the above. Wires, cap, rotor all pretty new, injectors all new, ALL EFI connections and GND's have been inspected and reconnected. All stock EGR and PCV functions are functioning. I dare say everything mechanical and electrical are independantly "OK".

 

I have two theories:

1) the big intercooler, pipes, and turbo lag more than stock so AFM reads air flow BEFORE the engine actually needs more fuel causing a rich period before full boost.

2)Tiewraps on the pop-off letting air out at 7-9psi cause rich condition which is then offset by higher air flows at 13psi.

 

Anyone have any more ideas. I am going to work on the pop-off theory now since its the easiest to test.

[cygnusx1]

Update:

Pop-off valve tightened down by adding lots of washers on spring. Still stumbles.

 

 

Theory 3:

Could the knock sensor pull any tricks to make it stumble and blow fuel out the tailpipe under mid throttle low rpm load?

[Afshin]

the big intercooler, pipes, and turbo lag more than stock so AFM reads air flow BEFORE the engine actually needs more fuel causing a rich period before full boost

Definitely not the case, the AFM flap opens in response to more air being sucked in the engine. so if anything there is lag between the throttle plate opening first (you pressing on the accelerator), then the AFM flap opening in response to greater air flow.

Check the AFM flap and make sure that it opens and closes smoothly, if it binds, it could cause erratic fuel mixture. Also if not already done in the last few weeks, unplug and spray ALL connectors to the ecu and afm.

no harm in checking fuel pressure and all vacuum lines (you probably already have)...

You can just unplug the knock sensor and see if it changes anything. the car runs perfect without it (it does nothing until it senses knock).

I would also try the car with 2-3 degree of increase and then decrease timing, sometimes it makes a huge difference.

Lastly 0.030) may be too little gap for that car, I would try it at .035-.038 range (factory is .039-.043). My car did poorly at .032 (with msd).

[fl327]

I would work with the ignition a bit after making sure the popoff valve isnt the cause. gapping the plugs in a big could help that stumble, are you running a msd or other ignition box, that could help it as well. Even stock boost my zx had the same issue, on a dyno it shows it as going rich as heck then backing out and leaning out, with the upgraded parts it may be exaggerating this effect with the afm efi setup. Just thoughts.

[Sean73]

Do you have an A/F gauge? If so, what happens when your cruising at 2500 RPM and no boost? Lights should bounce back and forth indicating closed loop mode. Although you have checked all sensors etc.., when the ECU goes into closed loop mode, you can get some confirmation that it's actually receiving the proper inputs.

 

In addition, I would turn down the boost to near stock levels and see what happens. This will help eliminate a few variables.

 

If the problem goes away at stock boost, then I'd say your pop-off-valve theory is something worth chasing after. Plug that thing and be done with it. Good luck

 

Sean

73 240Z, L28ET, T3/T04E, NPR IC, Z31 ECCS

[cygnusx1]

Thanks for the homework guys. Today I established that the popoff is not a source of the problem. Prior, this car had NO issues running with the stock turbo and J-pipe at 10psi. I used and still use the factory turbo ignition and fuel system. This problem came after I put in the TO4B, the Spearco and the Walbro Fuel pump. I had the plug gaps wide and narrow with no difference.

 

I will turn the boost back down and see what happens. I will also swing the base timing back and forth a few degrees to test.

 

Yeah it really loads up and plumes black smoke before it "catches" and hauls a55. It's like it snarls, smokes, and hesitates to warn me and then it just hits like a sledge hammer to the rear bumber and takes off.

 

Sean73, I dont have any metering tools but at night I can see the green LED in the ECU blinking about every 2-4 seconds green during steady cruising. It runs fine until I load it up from 1/2 pedal to 3/4 pedal. It sounds so much like the accelerator pump on a carb coming on too hard. Also the exhaust during normal driving smells cleaner than it ever has.

[cygnusx1]

"Icon with hammer hitting me on head" <--post one for me please?

 

SLAP ME SILLY!!!!!! This is the second time I have gotten bit in the A55 by the same gremlin and it still snuck up on me. I went over all the connectors and grounds by disconnecting them and reconnecting about 3 weeks ago to try to solve the rich stumbles and had no luck. This time I sprayed them heavily with brake cleaner inside and out. I also sprayed the guts of the AFM and, removed the main fusible links on the right fender and cleaned those connections until they shined. I took it for a spin and HOLY MOLY it runs smooth as a top and, this is the kicker, I didnt smell the exhaust in the car....I smelled the exhaust of cars in front of me..now THAT is a change. I also pulled away from a 911 convertible on a windy road. When I stopped at the intersection he caught up to me and beeped with a thumbs up. I am SOOOO happy that I want nothing more than to drive and drive and drive.

 

OK now I know I said I already cleaned the connectors in my original post but clean is not enough. They have to be CLEEEEEAAAAAAN!!!!

 

Thanks for all that listened to me babble and you all offered excellent advice.

[Guest ON3GO]

you can clean the engine ecu harnness connecters with brake cleaner?

 

mike

[cygnusx1]

I live in a fairly remote area where electrical cleaner was not on anyones shelves. I thought carb cleaner but when I looked on my shelf I had brake cleaner. Can you? I guess, I did.

 

BTW ON3GO, tell Alex Costa that the TO4B he built me is kicking butt.

[Guest ON3GO]

ah you got a turbo from alex?

nice turbo huh...

i cant wait to see what he does with my Z.

and ill deff tell him.

 

MIKE

[Drax240z]

Most companies sell brake clean and electrical contact cleaner that are exactly the same chemical, perchloroethylene. (PCE) Some other types of electrical connection cleaners are made from other chemicals however, and if you buy non-chlorinated brake clean it will be a different chemical than PCE.

 

PCE works just fine to clean electical connectors though, and anything with grease on it as well. (and suits too, since it was designed origionally for drycleaning)