Maybe your fuel pressure regulator?
Back with more issues. Looking for assistance from the friendly fox crew.
Car will run perfect for weeks then all of a sudden after the car is warmed up one day it will begin to shudder and misfire under acceleration like the fuel is cutting out when you press down the gas, kind of like if you hit the rev limiter but with longer intervals. If you play around with the pedal a little it will come out of it for a couple sec and go right back to it again. It is so bad the car will not pull a hill, huge loss of power. If you let of the gas the idle will some times move up and down, but never to the point of stalling. Park the car, fire it up next day it’s like nothing ever happened, it will run great for a day a week a month then do it again.
This happens irregardless of the amount of fuel in the tank, but only after the car has been driving for at least 30 min or longer.
What I have done so far: Replaced the distributor cap (plugs and wires are good). Replaced the fuel filter. Tested the transfer pump and the main pump per Bentley instructions (amount of flow in a measuring container for 10 sec (transfer) and 30 sec (main) both were good. Verified mechanical timing and distributor timing per Bentley instruction both checked out good. Replaced coolant temp sensor (the right one) with a new Bosh unit.
I did install an air fuel ratio gauge (was having issue prior to installation, figured the gauge could give me insight) I know its not correct as it could be as I am only using a narrowband 02, but its reads ideal or slightly rich when things are in order, and when it is messing up it is reading supper lean that’s why I was thinking it could be a fuel issue.
Not sure what to do now. Trying to get this issue solved as I am taking this car to H20
Thanks in advance for your help!
This sounds a lot like my problem from the last few years with my '93. I replaced all you did and more, and eventually suspected it was a wiring harness problem affecting the Digi somehow. Replaced: both fuel pumps, relay, checked pressure, replaced ECM, ICM, CTS, coil, dizzy, ground straps, plugs, wires etc. etc. Of course you'll check for vac leaks. Sometimes as a quick fix, pulling the CTS connector or other connectors at the side of the road would clear it up, at least for a bit. Hope you find it!
Not red, not blue- red, white, and blue
I have done this and it does work, wow Sounds like we are having the same issues and it has been going on 3 years now for me.I would replace a part and it went away for months then came back so I was just assuming somthing else went wrong. Its driving me nuts. About 5 months ago i took all the covers off the wiering harness, inspected and replaced a couple wires then re wraped everything and im still having the issue. I am not sure what to do now. Thanks for the insight though, atleast I know I am not going crazy. Are you any closer to solving your issue?...Sometimes as a quick fix, pulling the CTS connector or other connectors at the side of the road would clear it up, at least for a bit...
Solving, no... Resolving by giving up, yes Mine went on for about 3 years, and I started having tranny issues, plus frame rot. None of these were killers in themselves, but I finally threw in the towel. I bought the car new, ran the heck out of it, have two more Foxes because of it, and will miss it. It's slowly being parted out.
I still think it was a wiring issue somehow, and maybe yours is too. You're more persistent than me, and I bet you can find it. And then I'll be hitting myself on the forehead wishing I hadn't gotten rid of mine... Oh, well. Good luck!
Edit: dug up the old threads on it:
Last edited by reddfoxx; 08-13-2010 at 06:48 PM.
Not red, not blue- red, white, and blue
Thank you for the links, we have been down very similar paths it looks like. From your information and what I have done, I can’t see it being anything other than a wiring issue. I bit the bullet and removed the entire wiring harness from the car, laid it out in the drive way and went to work. I started with the digi computer harness (witch actually was not bad at all) then moved to the left side of the car and did the remainder. Thoroughly inspected each wire, removed all of the crazy cimp jobs vw did with the ground wires within the harness, made new grounds, replaced any questionable wires (soldered and heat shrink), and adjusted the length of a number of wires in effort to better hide them for a cleaner look. I then re wrapped everything in abrasive resistant tape. It took 3 days at 5hr a day. I have had all of this in the car for 1 day now (120 miles), so far so good. I noticed the car started quicker and had a smoother idle. The patches I have made before were not bad but this was a much more through job. Ill keep you posted. I think I am going to take it on a 2+hr out of state trip this week to see how it does.
Gosh I hope this is it. Though mine is an 88 CIS-E, I've had similar issues for 4 of the 5 years that I've owned her. The only thing that seemed to help for a short period of time was when I replaced my ignition coil. Good luck man, you'll be helping out quite a few of us here on the forums.
Back in for a 2 year update: a lot has changed (2.0 block, new head, cam, etc) Still on the original digi with modified harness. The issue is back! Drove about 300 miles or so on the new motor, issue free, all of a sudden this reoccurring problem… re occurs. Now, in some ways it is worse now than it was previously. You no longer have to drive the car into operating temperatures for the rapid rev limiter like misfiring to start. Some times it will be right from the get go, making the car almost imposable to start. Some times it will start perfectly and go into the issue 30 sec later. Unplugging the CTS no longer has any affect on the misfiring; it does it irregardless.
Any further ideas of possible solutions?
I think my next course of action is going to be to add a few wires to the harness, install an idle switch, knock sensor, and all the mkII based sensors along with the ecu. a relatively easy switch over; and I have access to a donor car.
Its ether a glitch in the ecu programming under certain conditions, or I overlooked something while going through the car. ICM, CTS, VAM, distributor, coil, plugs, wires, cap, rotor, wiring harness, fuel filter, have all been changed at some point, and the functionality of remaining items ( pump, idle switch, etc) have been verified, yet I am still having this issue… It is very frustrating none the less. Wish I had another fox digi ecu to install and try, its about the only thing I did not change out. I plugged in a MKII unit, and the car did start, but ran horrible, obviously do to incorrect input from wrong / missing sensors and circuits.
So you had the same periodic (but lasting when occurring) rapid, running on 3 cyl feeling misfires, but solved the issue as the idle switch was loose? So the car was not registering a closed throttle condition and it caused the issue? Or was the switch was loose and wedged closed placing the ecu in idle program even during part/wot conditions?
OK. I just verified switch wiring and function tonight; switch is working and adjusted properly, as well as a change in resistance is noted on the yellow wire during engagement / disengagement. It appears as though everything is as it should be on this portion, so we unfortunately may have different issues.
Engine bay is a bit modified:
I no longer have a cold start valve, or other idle adjusting solenoids installed (but i think there were 2 when i still had the equpment). The harness has been thinned of the associated wires. Needed grounds have been relocated, and several additional ground links between the engine, chassis, and harness grounds have been added. I wish I could attribute the lack of cold start valve to the issue, but unfortunately I had this same misfire issue with all the factory equipment installed as well.
I spent a little time cleaning the air temperature sensor within the VAM, as well as sanding off minor build up on the distributer cap, checking resistance values on the center “button”, as well as cleaning the rotor, and checking resistance values of the plug wires… everything is clean and within spec at this point. I was surprised at the amount of contact burn on the poles of the distributer cap, most notable on cyl #4… not sure if there is any correlation here or not, but this bosch cap has under 500 miles on it and did not look all that great. Had it out for a run today after all the work, and started it 3hrs after then 6hrs after, no misfires… but we all know how this story goes…
You are correct, one wire is the ground portion of the shielded signal wire from the osx plug routing to the ecu. The other wire is a ECU ground. Both grounds have been addressed when I re did the harness. As stated, I no longer have any idle assist systems in place; idle is controlled purely by the idle air screw on the throttle body (a mostly steady 700 rpm after a 30 sec warm up with the throttle depressed to 1200 rpm). Only 2 vacuum lines exist on the motor; one to the fpr, and one to the brake booster. All the other “fat” has been trimmed.
Had the misfiring issue again yesterday: Car was started a total of 4 times that day, all without issue aside from the 3rd time. Fox started normally, idled fine, I drove it about 2 city blocks when the misfire began, I continued driving the car and within 40 sec the misfire stopped and the car was back to perfect. That sort of condition really makes me what to think its temperature related… almost like there is a set temperature window (resistance values of the cts) that is out of wack and causes some sort of “compensation” causing the misfire. The issue has been occurring mostly during the first 1min of start up, if not from the get go. Unfortunately, unplugging the cts when the issue already started does not clear it up, but maybe because the computer was not reset and its still holding on to the values in some way? I am not entirely sure. I think the next time it happens, I am going to pull the battery, ground out the terminal, and let the car sit for a few min to see if the issue is still there when I restart the car.
I changed out an ignition rotor prior to my morning commute with the car (new rotor had about 2mm more meat on the contact point then the 500 mile-old one… strange as this replacement was from a 91 jetta, I will have to cross check part numbers, as I thought they were the same. I wouldn’t think a rotor would degrade that fast over 500 miles.) No issues this morning, lets see how the afternoon trip goes.
Thanks to Reddfoxx, there are 2 computers on there way to me. Thanks again!!
I did not even get out of the work parking lot when the misfires began on my way home.
I decided to spend the evening going through the digi harness one final time. This time, I took the all or nothing approach (rather than just replacing select wires as I did the last time) I separated the ecu connector from the rubber housing and replaced EVERY wire with a new section from a fresh spool. Each connection was cleanly soldered and heat shrink tubing was applied. I cut the old wire roughly 3/4” from the ends of the connectors, tested for resistance from this new end to the terminal and went from there.
When soldering the connections, I used ample amounts of flux, and a hot iron so the solder actually tinned the entire section of remaining stock wire, soldering it to the crimp connection within the connector housings. I really did not want to disassemble all of the connector housings if I did not need to. I also upsized all the signal wires by one gauge, the powers and grounds by 2, inserted a Deans high current connector in line with the throttle switch, and directly soldered the o2 sensor signal and heater wires. 9 hrs later I had it back in the car and running. No issues so far today.
Last edited by oRANGEJULIUS; 05-04-2012 at 10:02 AM.
i nevere have that problem with a cise unit maybe you should switch
Good news, no issues so far today… or at least I think so. I almost feel as though I had a slight misfire today but it was nothing even close to severe as what the car has been experiencing.
to tell you the truth im not using any extra injectors. just the four and meth injection never needed to use the extras that i intalled
Bad news ya still have a misfire for certain. Good news is its not as “heavy” as it was. Bad news is this complicates matters further being the new harness helped matters but did not make them go away. So I would assume this is electrical (sensor) related?
Thanks Reddfoxx!!! Got the ECUs today, super fat shipping. Thanks for packing them well, as it looked like USPS played a soccer game with the box before it arrived. No physical damage though. I pulled my ecu (car is a 1993) and this ecu corresponded in numbers with the ecu from 1991 you had provided me. Taking another look at the ecu that I removed, it was made in 1991 as well. It could have been a leftover, but I am guessing it is more likely that the ecu was changed before I got the car 6 years ago.
I installed the ecu prior to starting the car and unfortunately I still had the misfire. A light misfire that began roughly 30 sec after starting the car, and lasted roughly 30 sec before smoothing out to normal. I shut the car down, and installed the 1993 ecu you sent (diffrent part number)… I will see in the am if the issue persists. If it does, at the very worst I have an extra couple ecu as back up. If you need them, I will happily send them back, if not I would like to pay it forward if its ok with you, and offer one of them up (just for the cost of shipping) If a foxer is ever in need.
We will see how this goes. Does anyone have access to, or know of any technical manuals that discuss digi in DEEP detail? Looking for something far more informational than what is found in the Fox bently. I would love to learn exactly how this system works, all the details, and all the ins and outs. I have a good working knowledge, but a complete understanding would help a lot.
Last edited by oRANGEJULIUS; 05-05-2012 at 10:40 PM.
yeah you got me i don't know nothing about diji. but im an expert at cis-e units good luck to the troubleshooting
Last edited by vwturbofox; 05-09-2012 at 11:42 AM.
No problem; cts Circut has been changed along with the rest of the digi harness. In other news I am currently broke down on the side of the road as my passenger side axle outer cv joint decided it dident like being attached to the shaft any more. Great. Even better I found a parts store that had a fox axle in stock (1 hr away) had a friend pick it up for me. the axle was wrong axle... And I tore down the car in antisapation of installing the new one while he was on his way. So now I put it back together and waiting for the flat bed to take me home. Ahh fox ownership. I guess it could be worse.
Back on the road. Strange but good information: No misfires as of late. I have been letting the car warm up and idle for about 1min prior to taking off, I figured since all my misfire issues have popped up shortly after starting the car and driving off, I would give it a little time and see what happens, so far, so good. Not a solution to the issue, but its certainly making me lean even more to this being a temperature or o2 related (sensor, or circuit) issue. This is only happening in open loop. I believe digi does not shift over to closed loop until a certain temperature is reached (detected by ect sensor) Is that correct? Anyone know the temp this happens at? Or am I off base here?