BC

SAR = Some Assembly Required.


I have an 86.5 that I have deemed the "some assembly required" car from SC. It has high miles, but an apparent medium amount of work done to it. Interior was completely shot, but that's not germane here. It WAS painted, so it looks very nice as long as you don't look inside.

ANYHOO.

I have been having some drivability issues. It sort of hesitates/throbs at lower throttle inputs and rpms. I have cleaned the MAF and it has made a bit of difference, but really very little.

I also cleaned the grounds all over the car and replaced some important relays.

Yesterday I unplugged the 02 sensor for the ride to work, and it completely changed the way the car runs above 3k. WAY better. More mean sounding exhaust, and more torque and power.

Interesting.

The lower RPM problem is still there. Slightly masked by more power. Its still throbbing on acceleration that is not WOT. So (hopefully) out of idle and NOT on the WOT switch, the engine power will make your head bob forward and backward slightly. I hope I have described it clearly.

So today (in the rain) I decided to read the V on the 02 wire.

At idle its at .850v Rev it and it moves a bit but not much. Driving along it will go to 0 when you let off, and down to the 7s when you are accelerating through 4krpm.

Now - It will go down to .0xx volts at part throttle accelleration in higher gears - BELOW 3k.

What are your thoughts? Above a certain low rpm it recovers and goes back to to .7 and a bit higher. Thats just about the time the car feels better.

svp928

Brendan, you might PM Porken- he has vast experience with 86 electronics. And, get some of his chips for REAL good time....
My car had similar problems to yours at one time, it turned out to be the MAF itself was dying. I didn't do any voltage checks, but unplugging the O2 was going to be next when I discovered the MAF problem. I still have the orig O2 in mine, so far..

Steve

BC

Hey Steve. The MAF is quite possibly the culprit. The issue is that I know how much they are, and how truly fragile. The cost of that and a normal tune up starts to rival a Megasquirt installation.

Landseer

Brendan, don't jump to conclusions on it that require spending money.

I've got one here that's acting very similar. 85. Does better with O2 disconnected.

Very low on power, takes a lot of throttle, and there is a noticeable transition around 2100
Rpm. Real strange. Swapped the MAF and it ran the 86 car, and the 87 car of CPayne's, flawlessly. 86 MAF on this car made no difference.

Am wondering about a short in TPS ( its a possible misfire cause / Greg Brown found this the culprit in one of his customer cars) else a short somewhere in a harness.

Was hoping you'd solve it.

Rob Edwards

Brendan-

I've got a good MAF that's been on more cars than Linda Vaughn, shout and I can mail it to you for testing. If I'm reading PET correctly, the same MAF is good for 85 to 95.

BC

I do too! Thanks for your comments.

I was mentioning to my wife tonight after I did this testing that most people would probably just drive the thing and never even notice.

I am not one of those people.

It changes as the car warms up. Above 3500rpm it honestly goes like a raped ape, but I have only drive one other very high mileage S3, so it may be slower than I think it is.

I did not mention that I have also replaced the Temp sensor for the LH/EZF. I bought a new one from 928intl when I was up there for other things. I feel that that replacement was warranted, cheap, and a no-brainer. It has changed the way the car starts and idles innitially, but I am unsure right now if it made much difference elsewhere.

I did testing at the LH and EZF plugs for the TPS. It SEEMS to be working properly. That does not mean it is. The cheaper stuff I can and will replace at random with little thought because I know it needs it. I also tested the temp II sensor after replacement at the pins on the plugs, and I did ohm the proper pins for the MAF. It read alot of different numbers, but was 382 when that stuck on the screen. I bought a better micrometer and I will recheck.

The problem I am encountering in my mind as I go through this is that I know what the MAF replacement - or rather the IDEA of replacing the MAF means....(and I will explain that)

Realistically, there is little else other than possibly some ignition issues, and that system will be tested this weekend when there is less rain, and more time.

(pardon the basics - I am just reviewing for my own good)

If I am to understand what the voltage output of a narrow band o2 sensor actually means, then the car sitting as close to .845 as it can means THAT is 14.7 A/F ratio. The car, without this info COMING IN, is operating on a base map that is probably pretty damn close to that - but it will operate that map based upon a few sensors:

1) Engine speed sensor
2) VAC LINE to EZF (oh - maybe I should check THAT!)
3) Temp II
4) MAF
5) INtake Temp

I have not checked the first 2, and I think I should check the second one. Apart from that, all that is left is the MAF. I checked the MAF and its ohms were correct, but JDS always says that that means FA if its too old to read air properly.

If .850 is stioch, and there are sections of the rev range below 3k where I am accellerating without pinning WOT, and the number says ".050" and other stuff like .150 - that means that the engine is operating at SUPER LEAN A/F ratios when its trying to accelerate right? Thats 4th or even 3rd gear from low Revs, and then it only recovers to .6v -

That may explain why the car does so well with the o2 unplugged - its getting (if even only a little) more fuel.


If I have to replace the MAF, thats about 500 dollars realistically, for a real one thats from our preferred suppliers (rebuilt). If I do that, I am getting into the territory of "what else can I do" - at least in my world. Caps, Rotors, coils, wires, TPS, Vac lines under the intake, Reference sensor, as well as cleaning the injectors. That is dangerous territory, as there is other stuff (and people) I should be spending my money on, and its getting close to the cost of bribing Colin to come from the Nort and install megasquirt on a weekend.

I am going to check that vac signal at the EZF tomorrow.

BC

I may have to come and grab that from you if you wouldn't mind a visit. Even for 15 minutes of running in the car I can/would feel if there is a difference. Can you PM me your number? I promise I will put it in my Iphone permanently this time.

Landseer

Mine has new temp II, temp I, good vac.

I'm wondering about a lot of other possibilities.

Fuel filter, check valve, injectors / pattern / clogs (this car sat)

caps/rotors, coils, CPS

TPS; harness break, reversed wires to the TPS.

Car seems very lean.

Time to bite the bullet, rig up the oscilliscope, and work through the test plan systematically.

BC

I might top you on that. I have sticker for 1000 less miles as the oil change interval - and the date on that sticker was 2006.

Landseer

Mine went for a little nap in 1999 and wasn't restarted until mid 2009.
I just want it to run right. Let's keep comparing notes on this.
I've got one more week of wrenching on this 84, then the 85 work begins in earnest.

John Speake

If you can access a CO measurement tool, then you can check the MAF yourself by going through the idle CO setup procedure that's in the WSM. If you can't get the idle CO (before the cats) up to 1% then the MAF is suspect. Also check intake vaccum, a small airleak can also weaken the mixture causing lean out and bad running of the type you describe.

AO

Brendan-

IIRC the O2 sensor should read 0.5v at stoich. And the higher the voltage (up to max of 1.0v), the richer the mixture.

If your car thinks that it's too rich, it will try to lean the mixture out. This is probably why you're having issues at above 3k but goes away when you unplug the O2 sensor. But I suspect there are some other issues causing your problems at idle - perhaps the MAF is out of whack, leaky PFR, leaky injector, etc.

Do you have a wide band O2 sensor you can stick in the tail pipe to verify the mixture?

BC

Lower voltage may mean richer, and higher voltage may mean leaner. I could be wrong before or here. The reverse is true on several charts I have seen. The car does not feel rich at lower rpms. It feels lean. Obviously I need to check this. One way is to see what happens with a different MAF.

I'm confused because there are lots of charts that reverse themselves when they go away from 14.7 A/F

BC

I don't have access to a CO tester from what I can imagine. I could/would buy a wide band 02, but I think the CO tester is a complex machine right?

John Speake

Gunson make one that is good enough to get a good result....
http://www.autoexpertproducts.com/gastester.htm