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Discussion Starter · #1 ·
here's the story.....a lil long, i'll try and keep it as short as possible.
bought an 89 helios. timing belt stripped.....opted to pull the head to check for damage. none. then decided to have it PnP'd while i had it off, in the mean time, i redid the whole car....new suspension, roll cage, complete non a/c swap. along with all this, i purchased a refurbished block (freshly honed and painted and what not) and all the goodies to go with it. all new bearings, rings, rods, that kinda jazz....put it all together and dropped the motor in.
had a heck of a time getting the thing to run....found out later that i actually had the coolant temp sensors hooked up backwards. swapped 'em, still had troubles with it getting too much fuel. mind you, when i got the car, it was stock. had to drill the fuel dizzy out to play with the mixture screw and even then, i didn't play that much with it. finally bucked up and took it to a shop up north of seattle. found out THEN that one of the two sensors was bad and i got it replaced with a new one, he got it running, timed and apparently got the fuel mixture set.
i installed an Autometer pro-comp ultra light a/f guage just for kicks (bought it new)...and the thing doesn't work. only in the dark can you see anything, and it's down all the way on the lean side, BARELY lit up. if i unplug it from the o2, it goes to full rich, like it's supposed to.
after i had some issues with that motor.....i put ANOTHER one in....this time with a bigger bottom end (83mm pistons), a true 2.0. did it all myself, i've got it timed, but the fuel mixture is giving me problems. the car runs great, idles fine, gets great gas mileage, doesn't run excessivily hot (maybe from it being lean)....but when i hook up the DPR test harness, it cycles down from 25 or so mA down to 14.2 and stops dead in it's tracks. it doesn't go down to say, 14 or even 13.9 and bounce back up, it just stops. you turn the mixture screw to richen it, and it does nothing. if you unplug the o2 sensor it does nothing.....does nothing if you ground it, and does nothing if you hook it to straight power on the battery. if you check the voltage coming out of the o2 sensor (its' brand new from VW), you get proper voltage from it, and you can watch it adjust according to the mixture (if you richen it, i believe it goes up, lean it, voltage drops), so it's doing it's job.
i was told to replace the ecu........did that. nothing changed. then told to redo the grounds going to the engine.......redid the ground that goes from the valve cover/dizzy area to the coil strap, then ran a cable from there to the battery negative...so i KNOW it's getting a good ground (nice 8ga wire as well). still nothing from it.
how could it be "so far" out of whack having never turned the mixture screw more than 180*? i was told that when you pnp a head, it'll lean out.....but if you go to richen it, it just dies.
a friend of mine said that it could just be so far out of adjustment that it's setting itself to full lean and running that way.....but just last night i turned it a little rich and i can smell the extra gas in the exhaust...
i need a pro to help me out on this......what's the deal?
 

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Re: fuel mixture woes.... (DCI VW)

Quote »

i installed an Autometer pro-comp ultra light a/f guage just for kicks (bought it new)...and the thing doesn't work. only in the dark can you see anything, and it's down all the way on the lean side, BARELY lit up. if i unplug it from the o2, it goes to full rich, like it's supposed to.

Sounds like the gauge wasn't installed correctly. These things can be quite sensitive to input voltage and grounds.
Quote »

but when i hook up the DPR test harness, it cycles down from 25 or so mA down to 14.2 and stops dead in it's tracks. it doesn't go down to say, 14 or even 13.9 and bounce back up, it just stops. you turn the mixture screw to richen it, and it does nothing.

Well, apart from a bad ECU, which you've ruled out, this could also be caused by bad idle/full throttle switches on the throttle body, or by a bad DPR. Sounds like it's not adjusting the mixture at all, always running at the baseline setting you set with the screw. If it was really going full-lean, it would run hot all the time, which you say it doesn't.
 

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Discussion Starter · #4 ·
Re: fuel mixture woes.... (Oms)

it's got a new dpr on it, and the throttle switches tested good AT the ecu.....
 

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Re: fuel mixture woes.... (DCI VW)

i had a similar problem on my 16v swap. to make a long story short, if you look at the dpr current on a scale of +14ma to -14ma the higher positive the leaner. i had my leads backwards and it wouldnt move from +14ma no matter how far i turned the screw. when i realized this - i reversed my leads and leaned it out from -14ma to the correct +2.5ma for my 2.0l 16v motor. now she purrs like a kitten.
maybe its something to try if all else fails...
 

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Re: fuel mixture woes.... (mk2dubbin)

Get yourself some more accurate gauges. If you've got the money for all that engine work, you've got the money to get a wideband o2 sensor, check out diy-wb.com.
 

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Discussion Starter · #7 ·
Re: fuel mixture woes.... (porschedoc)

ummm......if that's the actual web addy...it dont work.
maybe the complete link?
thanks for the info....
 

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Re: fuel mixture woes.... (DCI VW)

Have you verified that the wiring from the o2 sensor to the ECU is good?
 

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Discussion Starter · #10 ·
Re: fuel mixture woes.... (89GLI16V)

Quote, originally posted by 89GLI16V »
Have you verified that the wiring from the o2 sensor to the ECU is good?

not yet.....didn't think about that till after this post......waiting to get my bently back to do so.
 

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Re: fuel mixture woes.... (DCI VW)

I post this info as much as possible... I hope if you read it you can take what part applies to you and it will help
The last paragraph describes how I tune all the CIS-E cars I work on.. hope you find it helpful

"This problem" mentioned below refers to a slightly different illness but every injection problem inheritly is the same symptoms.

Fuel Pumps are one of the more common causes of this problem. This is the easiest check I know. Sit in the car and turn the key about 10 times (dont go all the way over to start it). If you hear your out of tank pump get severely weaker and weaker... it might be biting the dust, or your in-tank pump is bad. To check the in-tank pump, pull up the mat in your hatch/trunk to uncover a plate with 3 screws in it. Remove the plate, and have someone turn the key again and listen to see if the pump is running. The easiest way to tell is just to unplug it and plug it back in. If you hear a difference, good! you should. But if it doesnt run.. then change it out. The out of tank pump will suck right through the in-tank accumulator pump... but the in-tank pump is just that... an accumulator pump. Making the out-tank pump work extra hard to get the fuel can cause lower fuel pressure and what you are describing. It may burn out your out of tank pump as well.
Change the fuel filter while you are at it to, see if that doesnt help.

Vacuum leaks can cause many problems with idling and hesitation. Inspect your intake boots for rips. It is fairly common to find a ripped or torn intake boot as the culprit of your problems. Collapsing or old vaccum lines are culprits too. To check for un-obvious leaks its really simple. Spray some brake clean in a small amount around suspect vacuum connections. If there is a LEAK there... your idle will increase. Key places to check with this method: Your injector O-Rings, around the brake booster, the brake booster vacum line connections, any vacuum lines. Another uncommon place for the problem is the lines that run into the firewall. They can go to several possibilities... your ac controls, knock box, and instrument cluster. Jarring them can accidently pull them out of these units and thus create a leak.
Misadjusted flapper valve, Air position sensor plate for fuel distributor. This causes a bad mixture condition and can cause it to hesitate and cut off and all that. If you pull your intake boot off the top of your airbox, the plate that is sitting there.... put a nickel on the side of the plate closest to the headlights. If the top of the nickel rests even with the lip there then your ok. Otherwise you might have to adjust the spring style clip that the plate rests on. Its tuff but you can do it. Dont touch the bolt on top of the plate, thats for horizontal adjustment. Any adjustments made to the resting height of the plate will most likely require re-tuning the mixture.
Check the ISV by unplugging it. IT doesnt do much of crap unless its dirty, and that will cuase your car to have a rough idle. If the mixture and timing is set correctly then you wont have a problem running without it. IT plays a more important role on digi 2 but its nothing the idle air adjustment screw cant handle on CIS-E. There are lots of people running around without the ISV
A more common cause of bad idle/Heisitation is bad plugs or clogged/dirty injectors. Injectors are a very common cause of this. To test injectors its really easy. Pull them out, and stick em in a bucket. Take off your intake boot on top of the airbox. Place a jumper wire caross the correct terminals on your fuel pump relay... the two big male spade terminals on the relay. Use about 12 gauge wire. Go back out and simply lift up on your flapper valve plate in your air box while directing the injectors into a bucket. If the spray pattern on any of them is crappy as in its not a mist..... then its bad. You also might want to think about pulling your fifth injector to make sure its not spraying or weeping when you pull up on the plate. Now would be a good time to replace your O-rings too...
This problem can also be caused by a bad oxygen sensor/temp sensor which is causing your Differential Pressure Regulator to misadjust the fuel mixture. If you hook up a ammeter inline to adjust your mixture on the DPR, you can find out easily. If while making small adjustments to your mixture screw you find the DPR current to hang around 10 or 12ma and/or not move.... your OX sensor is bad. Each adjustment should be seen by a different DPR current. You can try unplugging the oxygen sensor to see if it makes a difference.
Tips for adjusting fuel mixture. Get the car to operating temp. While adjusting the mixture, unscrew the idle adjustment halfway out, and unplug your ISV. If you get a nice T-handle 3mm allen wrench, you can put sideways pressure on it and pull up and push down on the air position sensor plate. Because you can do this... I unplug the DPR and pull up or push down on the plate to keep the car running until I can turn the screw enough so that the plate sits in that position. I then get the car idling really smooth by making adjustments on the mixture screw... and then I hook the DPR back up and fine tune the current. Remember, a hair of a turn goes a long way! Although you may have to make a few initial large adjustments. If your ox sensor is bad, or your whole everything is bad... you can still get your car running fairly well with this method


 
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