random richness, details ... PROBLEM SOLVED

[silviasgp06]

ok, after research and checking different item on my car im still stumped.

my setup: Stock rb25, stock boost, 3"exhaust, Apexi power intake, PFC with stock apexi tune.

Symptoms:
Random richness and huge loss of power. Richer than 10afr at some points after start up (sometimes) and sometimes wont idle with out having to press the gas peddle to keep the rpms above 1000 for like 10 seconds. After the car is able to idle the AFRs remain rich, then eventually go away. Driving at sustained speeds when this issue surfaces the AFR is around 11 or worse and if the gas peddle is pressed to accelerate the AFR reads full rich and the car bogs down loosing power due to richness. Mis- fire and sputtering also happens during this event.

And then there are days that it runs just fine....

Things Ive checked:
--O2sensor Volts on the "sensor check" (or what ever its called on the PFC commander) do not jump around in sync with when the richness so i do not think that its bad.
--I check the 12v power to my, MAF, coil packs and its seems good
--PFC reads 14.4V during cruise and while driving. Also remains at 14v when the event happens
--Connection for the ECUs water temp sensor is not loose but this doesn't dismiss a COOLANT TEMP SENSOR issue from what Ive read.
--MAF was cleaned with MAF cleaner to no effect
--FPR at idle doesn't seem to drop during the event.
--Plugs are properly gaped
--Checked for boost leaks.. none

-- --the one thing I just realized I haven't checked is what is how timing is acting during all of this.

possible guesses so far:
--coolant temp sensor
--MAF or O2 sensor going bad
--Coils going bad, or low volt issue
--injectors going bad or low volt issue?
--alternator going bad
--PFC coil pack controller going bad...
--valves intermittently not sealing, or just leaking more at sometimes...i need to do a compression test to remove this possibility

So those are my symptoms, what I've checked for and what people have said it could be in other posts.

What do you guys think?
is there anything anyone may know that could help me narrow the problems down before i start spending money buying replacement parts?

let me know if you have any questions, ill elaborate if needed

Ill have pizza delivered to the person who comes up with the solution!!!

[silviasgp06]

edited.

Anyone able to help?

[Joe]

TIMING, check that first.
use your PFC to check out your MAF at idle and while driving
also your coolant temp sensor, make sure it reads a real temperature that changes as the engine warms up.
check your TPS with key on engine off for the full sweep of voltage. ~.5 closed to ~4.5 wide open. MAKE SURE THERE ARE NO DEAD SPOTS.

[Joe]

TIMING, check that first.
use your PFC to check out your MAF at idle and while driving
also your coolant temp sensor, make sure it reads a real temperature that changes as the engine warms up.
check your TPS with key on engine off for the full sweep of voltage. ~.5 closed to ~4.5 wide open. MAKE SURE THERE ARE NO DEAD SPOTS.

i like pizza hut stuffed crust pizza with jalapenos, pineapple and canadian bacon. :p

[S12_hybrid]

I have been having quite literally the exact same problem. Very intermittent, very very irritating.

Do you have use of maybe the first 1/2" of accelerator pedal to use, otherwise it misfires and sputters? I do not have an AFR but I can tell it is not getting complete combustion (black smoke! it stanks!), and I know my ignition timing is set to 15 deg BTDC. It must be overfueling and pulling timing as well.

Maybe we can collaborate on this, and then order each other pizza!!

Specs:
-1987 200sx
-Series 2 Rb25det
-stock turbo
-fmic w/2.5" piping
-greddy intake mani
-2.5" exhaust
-walbro 255 fuel pump


I have done the following:

-Gapped plugs .8mm
-Checked TPS voltage across the range, reads normal, no dead spots.
-Checked ecu grounds
-O2 sensor has power and continuity to the ecu for signal
-Temperature sensor reads normal, connector is broken but taped and is not short circuiting
-New fuel filter
-New fuel pump
-Turbo is in good shape

Have not checked:
-Knock sensors
-Cam angle sensor (aside from it being in time)
-Maf voltage readings with/without air being blown through
-Full harness dissection/diagnosis



There is a diagnostic procedure for the Rb25det maf in the R33 FSM (available online) that I am going to be going through tomorrow, maybe try the same?


-Dan

[S12_hybrid]

I think both our issues are MAF - centric..

car-starts-and-drives-up-2000-3000-rpm- ... 92489.html

I think my issue is that I have the wrong maf! I've got a 4 pin maf on a series 2 - but the thing is that it was running absolutely fine for the longest time so I let the sleeping dog lie. So yes, get the R33 fsm from the web, and check the wiring, and check those voltages!

-Dan

[silviasgp06]

S12- sounds good on the pizza!
I have a copy of the FSM so I will get to it.
On your MAF statement.. what MAF do you have? A S1maf on a S2? not sure if thats an issue if you have it wired right but I may be wrong.

Joe- Some reason I am unable to get a stable reading for timing. Whether I clip the timing light to the harness loop(on the coil harness) or the #1 signal wire (right next to the #1 coil) when I look at the timing marks the keep moving back and forth 5 degrees at a rate of like 10times a second. I revved the motor to see if it stabilized at a higher rpm and it does past like 2000rpms, but at Idle it doesn't seem pick up a stable reading. At idle the PFC says 14v so I don't think its a alternator low volt issue.

Also I can not seem to adjust the screw to get the car to idle below 700 anymore.(I used to be able to get it to 650ish with the TPS unplugged to set timing) it just bottoms out. kinda make me think there is a vac leak somewhere but boost leak test didn't show that.

MAF-- forgot to have details from my previous post about my MAF readings.
the MAF volt at like a 800rpm idle are like 1.5v and dont make any random jumps through the rev range. however it does hit 5.1v around and above 5000rpms. This was an issue I was posting about before I started to have the current random richness issue.
-How can the MAF be maxing out on a stock boost rb25 when no apparent boost leaks?

Checked my TPS and it read ~.32v so I adjusted it to read .60v. Did not seem to solve richness issue. it smoothly transitions in volts with no dead spots or jumps

Coolant temp sensor gives not odd reading while warming up. Since Ive had the car the average driving temp is 80c(176f) a little warm I know, but I have pusher fans in from of the A/C condenser and need to make proper ducting to control the small amount of escaping air.

No high knock reading when the issue occurs

[Joe]

you should have to adjust the idle via a screw

check your IACV and connections.

[silviasgp06]

Thats what I did, I am able to adjust the idle using the screw on the IACV, it just won't go below 700 ish.

[S12_hybrid]

Problem = fixed.

I performed the maf diagnostics, the maf tested out OK. I then turned my attention to the wiring. When I got the car it had the pigtail cut off, so I connected one from a maxima in it's place. Oddly enough this wasn't where the problem was. The wiring had been pinched and bent, and there was a break in the wiring that essentially meant the signal wire was grounding out on the shielding.

This then made me think, since the shielding is essentially small gauge wire surrounding the signal wires ANY break will likely cause a short to ground. Even if your maf wiring shows continuity back to the ecu (which mine did) on pins 26/27 you may still have a short. To quickly test see if you've got continuity to ground on either of these signal wires, if it is a very low resistance you've got a beefy short. Also, check the condition of the shielding, where I had spliced mine together had become quite mangled, so I redid this all..

So check your power, and ground to the maf, and then check the signal wires for breaks.

-dan

[silviasgp06]

S12_hybrid,
Glad to see you fixed your issues.
Back when I lengthened the MAF harness back when I did the swap I use a shielded harness but never connected the shielding. I did this the other day but there was no effect.
Is there a proper way to do this?(splicing shielded harnesses) How did you do it? Photos would be awesome for me and for future reference to others.
I will preform the tests and see what happens.

[S12_hybrid]

Well that is the issue, I didn't actually repair the shielding, I removed the pigtail which I had added in before. Shielding is meant to cover the signal wires and have no breaks in continuity, so make sure the signal wires are surrounded in it , and that the shielding wires interweave as best you can make it. Chances are there is an issue with where the signal or power wires are spliced, and the motion of the engine moves them just enough to break/make the connection, thus leading to inconsistent results.. At least, it is a theory.

-dan

[silviasgp06]

before I received your reply I went to Frys and bought some new shielded wire, so Im just going to re do the MAF wires from the ecu to the MAF unit. Cant beat $6 for 25 feet. It was 2 pair Shielded, so there are 4 wires wrapped in shielding, so I will have 2 unused wires, but this shouldn't be a problem. looks just like the OEM wire though. I may re do the O2 sensor wiring the same way as well. Ill let you know how it goes this afternoon.

also how did you preform your MAF diagnostic?

[S12_hybrid]

I followed the r33 FSM guide.

Be careful with that wire you bought, many telecom wires are given in what is called a twisted pair to help avoid crosstalk, it may not matter since this is an analog signal but try to use the wires in their respective pairs, not one from A one from B.

http://en.wikipedia.org/wiki/Twisted_pair

-dan

[silviasgp06]

S12,
well looks like I owe you a Pizza! I re wired it from the ECU to the MAF and properly grounded the shielding and I do not have the richness issue any more, car is a blast to drive again(kinda). Now I just need to get a more stable ignition signal for my timing light to re-check timing and after that I should be able to start street tuning(after i find the high duty cycle culprit).

but regarding your note on wiring. The wire I used wasn't shield like in pairs. It was 4 22 gauge wires and one uninsulated wire as part of the shielding all together wrapped in foil. Not two separate shielded pairs. This should be a problem right? Seems like my problem is solved though.

only thing is above 6500 rpms I the injector duty cycle inches above 90%.... not enough to trigger the above 90% CEL flash from the power fc, but when I viewing the data maxes after each test run the readings are pretty high. I still need to go back and look at the MAF volt maxes in the morning to get a better Idea on whats going on. Good news is the main issue of richness seems to be gone, now im just back to why a stock boost rb25 is getting 90%+ duty cycles at high rpms, seems like its still MAF related...

[S12_hybrid]

Woohoo! great news!

I prefer Hawaiian, but you'll need to order for delivery to Canada.

The 22 gauge wires should be fine, I suspect the analog signal to be a very low power one - but this is just a theory. As for the foil, this too should be fine it is just another medium in which to encase the wires.

Now hopefully, when others have similar problems they will find this post and solve their problems!

If the IAC valve adjustment doesn't seem to work, make sure to check throttle cable tension, for vaccuum leaks, and ensure the main IAC air source is routed pre turbo/post MAF - otherwise you will be idle hunting all day long and especially whilst the engine is cold.

-dan

[silviasgp06]

I was finanally able to get a stable ignition signal and my car was timed at 0*, adjusted it to 15* and the car is lightning fast now just on stock boost. Cant wait for how it feels on 12psi.

S12, what major pizza corporations do you have in your part of Canada? Pizza Hut, Mr. Jims, Pappa Jons Dominos, or any other place that I can place an online order lol