82 L28ET lean out top end issue

[stupid_fast]

Hello All,


I've been working with Rayapp2 diagnosing this for a while and we're both stumped. 

I can setup the motor fine, at this point I've gotten it to run.  does 10:1 in boost, pull around a bit when its hot... after around 5 minutes of this it will start to lean out starting at the top rpms and get progressively worse until I can only drive part throttle and barely limp it runs around 18:1.   Takes about 5 minute to get to undrivable.

 

if I cut the ignition and start it up again, it will go back to running normal and 10:1 in boost.  the issue comes back faster after that. 

I have an innovate MTX-L reading afrs

1982 L28ET with 1983 ECU i have spare ECU's that I've tested.

AFM is reman unit, I've swapped and tested anther unit and tuned with wideband. 

all harness connectors have been replaced with kit from fricfrac

ecu connectors are Z31- I've even swapped some of the pins to z31 and retensioned, soldered them!!  no more intermittent issues here.

CHTS is new OEM nissan, I have three more than ray lent me for testing.

engine is mechanically sound, I just did a pre-track teardown to check the head gasket and internals.

CAS looks to have been replaced at some point.  timing is steady @3000rpm

TPS is adjusted and tested per FSM

Ray personally went through the system and thought the injectors were bad ... I put new ones. in a few days ago no change

fuel pressure is factory spec, flow is good

 

what else? probably forgetting something.  just flying blind at this point, pouring over wiring diagrams testing random wires.

 

 

Any ideas?  Anyone intimate with the inner workings of early ECCS systems? 

note, I am in california.  I need the stock ECCS to pass smog.  Z31 swap is not an option.

Edited May 14, 2015 by stupid_fast

[Tony D]

This sounds like an incomplete 'reman'...

Like a solid state component internally is warming up during use or a capacitor on the board getting overcharged, causing a biasing to the fueling curve... Resetting the Capacitor when you turn it off and restart it again.

 

I had a compressor doing this with a display value. A broken trace in a multi-layer PCB was overcharging a capacitor and it biased the circuit for one of the readouts. You could see it jump up during startup, and then progressively discharge and let the reading return to normal (once we turned up the trip point to where the high-charge point wasn't a tripping point.)

 

That's what it sounds like to me.

 

Or Ray is just spending too much time doing those Black Chickens like he's wont to do, and just stringing you along till the next big black chicken comes along to satisfy his needs.

 

 

And regarding "Needing Stock ECCS to Pass Smog in CA"... You need to LOOK LIKE you have a stock ECCS to PASS Smog's Visual, and need SOME system that will maintain the mixture properly and function the EGR properly to pass the dyno check. That's a bit different than what you stated. There's the law, and there's reality. There is a group of VW Bus Owners in SoCal that were in on a Group Buy back in 2001 who have been passing smog on their VW's for over a DECADE now since changing to something that actually held the calibration and wasn't 40+ years old filled with desiccated capacitors bleeding the factory calibration of the ECU all haywire!

Edited May 11, 2015 by Tony D

[stupid_fast]

Thanks, I was thinking the same thing.

 

Could it be fuel pump related ? I was also considering checking running voltage make sure the alternator is in spec. 

Ray mentioned the capacitor issues... 
I put a new 63v 100uf  barrel cap in one of the spare ECU, but the rest are tantalums and are a bit harder to get locally. I'll be ordering them.  I have 3 ECUs, one with an intermittant power issue it'd be nice to restore them all if I can. 

 

What else has capacitors outside of the ecu?

Was thinking the CAS and timing can also cause fueling issues, looking to test another one. 

 

 

as for 'looking stock' I was chatting with ray about that.. 

I'm ordering a megasquirt kit soon, going to get it working with the stock harness maybe add some wires for extra sensors.  But I need to get the money first.

I have to smog it on the 20th or non-op the car, but I'm pretty sure I could pass in its current state after tuning the AFM. 

Just wanted to hear a proper reply and not 'go z31/megasquirt' as a canned response.  I guess I've been spending too much time on facebook groups.

 

 

 

Anyone local to north bay area have a CAS they want to lend me... for science?  

Edited May 11, 2015 by stupid_fast

[cgsheen]

You could pull the CAS out of a newer Nissan at a yard...  The distributor type VG30's in the Maxima's, Infiniti M30, Z31 use the same optical module (different package, the top of the circuit board isn't exposed).  They're slightly different than stock, but they'll bolt in and use the same plug.  The only problem I've had with a CAS is a "intermittent shut-down" deal caused by a broken solder joint...

 

To me, it sounds like fuel.  Don't forget about pressure and VOLUME.  You can have a restriction that doesn't show a decrease in pressure, but will definitely affect volume. Return lines?  (sounds like it's picking up something and clogging, then falling off / opening up and picking it up again?)  Otherwise you have a really unusual fault...

[stupid_fast]

My CAS is one of the later covered style ones. I assume it was replaced at some point I will grab one from a yard to test.

Its not a mechanical fuelling issue. From 18:1 in boost cut the ignition, start it back up while rolling, do another pull and instantly at 10:1 again.  I tried 4-5 times to verify it was a repeatable result. 

If its fuel pump, its electrical. I will swap back my spare n/a pump to be sure.

Also had another idea, I havnt checked running voltage the alternator could be out of spec & over-volting the components.

Edited May 11, 2015 by stupid_fast

[Tony D]

Corkage regulation on the front end of the ECU should make over voltage moot issue. It all operates near 5VDC.

UNDERVOLTAGE on the other hand makes for massive board level amperage increases and fries components.

 

Really, the answer is to,toss the ECCS....unless you do a competent total system overhaul of all board components yourself you are never sure who decided a component was "good enough" and that tolerance stack adds up to be an issue.

 

 

The change from stop to restart says there is a bias building up that is discharged when you turn the key off. To verify it, you could stick an automotive meter or o-scope that reads duty cycle of the injectors....you should see the pulsewidth change. That is the key...if the pulsewidth narrows on the scope as you run, then gets wider after you key off and back on, it's a bias in the electrical,side of the circuit.

 

If you see a WIDE pulsewidth that NARROWS after your key off back on, then it's a fueling issue...but I don't know if this second characteristic would be exhibited on an older system as the pulsewidth is set over 3500... Basically by rpm with the WOT switch closed...

 

I think you will see the first characteristic...the preprogrammed pulsewidth set by basing components on the board to be set and give set fueling through a given rpm load point slope. If a component is failing, then it will start affecting that pulsewidth. If it returns to the original pulsewidth after key off, you isolated it to the board. To find the component....

 

Well, maybe JeffP is feeling generous and will cut you a break to pick apart the board components. He's reverse engineered the Z31 ECU Board...but not the earlier ECCS...maybe it would intrigue him enough to ferret it out.

 

 

But a current generation ECU with programmable fueling points and better processor can maintain the same emissions performance of the earlier boxes, allow for troubleshooting, and...well...keep you from getting in the bind you are currently experiencing!

 

Good Luck. If Ray Mayes it to Bangkok, I,found the Sheep Farm, and it even has ducks and chickens to satisfy his urges along those lines!

[stupid_fast]

Very useful, narrowing down the troubleshooting.  Thank you.

That automotive meter looks cool.. but I'm unsure how much usage it'd get by me.  I don't have access to an o-scope right now.  I'll see if someone I know has em after a couple more things to try. 

I am looking into megasquirt but it would be a long and expensive project right now, just want to get out on track for some practice and finish blowing up this block. 

Probably going to order MS3... But researching all the options first. 

Edited May 14, 2015 by stupid_fast

[Chickenman]

Double post...

Edited May 23, 2015 by Chickenman

[Chickenman]

Could also be a fuel tank venting problem. Drive around till problem occurs then pull over. Leave engine running and quickly remove gas cap. If you hear a big Whoooosh... you have a venting issue. A partial Vacuum builds in the Fuel Tank. Fuel pump pressure may read OK at idle, but can't maintain pressure under load, particularly on a Boosted car. ( You need to have a FP Gauge set up and readable in Real Time while driving under Load ).

 

When you shut the engine off, the gas tank will gradually pull air in from the gas cap, alleviating the problem for a short time. Improper deletion of Evaporative  Canister ( Charcoal Canister )  system can be a major source of fuel tank venting issues. People may plug off the wrong Charcoal Canister lines and don't realize that they have just plugged off the Main vent line to the Fuel Tank.

 

Note: Emissions fuel caps are, for all intensive purposes, " Non-Vented " They will vent a small amount, but not nearly enough to prevent a vacuum from building in the Fuel Tank.  Up to about 1971, Datsun used vented gas caps. Then they switched over to Emissions style starting around 1971 1/2.

 

You can also drive the car around with the gas cap loosened if you suspect a venting problem. If problem goes away then you have confirmed the issue. Obviously do this on a half tank or less and don't go throwing it around corners or accelerating hard. And carry a fire extinguisher!!

 

Edited May 23, 2015 by Chickenman

[stupid_fast]

My car already has a fire extinguisher.  

I will try it. 

 

 

 

 

 

edit,

 

Went for a drive.  The issue is a lot better after a ton of fiddling with everything, idk. 

Now its only leaning out above 4000 or so.  below that making good power, and it only starts up after 10-15 minutes or so of driving.

All of my emissions equipment are intact and functioning, including the charcoal canister.  I checked the gas cap after the issue started up, there was no pressure build up. 

Edited May 25, 2015 by stupid_fast

[aarang]

Check the EFI relay. I had one that was getting hot and did almost the same thing. Just like Tony said, the ECU does not like low voltage. I wired in a new generic relay and got rid of the fusible links and the problem went away. Check resistance and voltage at your fusible links for the ECU and injectors if you still have them, especially after the engine has been running a while. Also, what is the state of your alternator/ battery? Just some things to consider.

[stupid_fast]

alt/battery less than 2 years old.  voltage holds at 14 idle, and I leave the car sitting for a week or more at a time without losing a charge. 

I will check the fusible links. I've had issues there before, didn't think to swap those yet.  Already have spares.

Edited May 26, 2015 by stupid_fast

[Tony D]

"alt/battery less than 2 years old"

 

That says "I'm taking things for granted, skipping them on assumptions, and I don't know what happens yet when you make assumptions."

 

Ask Ray.

[stupid_fast]

I don't see how its making an assumption when I did all the work?  I checked the running voltage I don't understand what else could go wrong here? 

Edited May 26, 2015 by stupid_fast

[Tony D]

Nice Edit.

[stupid_fast]

?

 

 

edit, its also running lean when cold.  Could be significant, or could be a different issue. like 17:1 idle on cold start.  Fires up no problem though.  

Edited June 2, 2015 by stupid_fast

[aarang]

Lean when cold should point you in the direction of the CHT sensor. Slight resistance changes in that circuit change the fueling pretty dramatically. You stated that the connectors have been changed which is a good start. The wiring in these cars is 30+ years old now and does break down with time. I have taken numerous harnesses apart and seen the horror that lies beneath, and have had temperature related drivability issues that were directly related to the wiring itself.  Maybe try running new wires from the CHT to the ECU, or at least check resistance of the wires between the CHT and ECU both cold and hot. There is a resistance/temp range chart in the Service manual that gives the proper values for the CHT signal to the ECU.

[NewZed]

WAG - the ECU needs dropping resistors and you don't have them installed.  ECU injector transistors overheat and stop working right.

[aarang]

83 ECU doesnt use external dropping resistors, although that is a good point about the injector drivers overheating. What type of injectors are you using?

[stupid_fast]

They're stock 280cc factory reman flow matched injectors.

 

 

I'll check the wiring