Hey everyone - So, I'm driving my Mondial yesterday and well, I'm getting a nasty misfire right around 4-5000 RPM - it's in any gear, doesn't matter what. I don't get it.. I have done the following to try and remedy, but I'm tapped out of ideas. I had read in some previous posts about some sort of module or plug or something on the intake plenum? I don't know.. Anyway, the following is complete. New Plugs / Wires Caps inspected / cleaned - they look like brand new - didn't replace. Other than that I'm not sure - the only other thing I can think of is maybe the plug extenders or the coils? But why would it run fine until higher RPM? Possibly a weak spark I guess. This could be a common thing, I don't know. My Mondial is the 8V not QV, FYI. It's an 82. Thanks!!
OH yeah.. and my tach pretty much has a mind of it's own.. could be related, could not.. ? Dunno. Just trying to give as much information as possible. Anyone have any ideas? If it is the coils, which ones are the good replacements? Can I source them locally? I need them TODAY..
Have you added the extra ground wire on the Digiplex units? Mine did something similiar and this solved it (1982 - 308).
an extra wire going from both units to ground. (located on underside of L/H panel in rear compartment on gts qv) there is already a body ground lug there. Image Unavailable, Please Login
No SH*T... seriously that helped your problem? Was it similar to mine? I'm just in awe that might be it... Can I ask a dumb question - why does this work? What's the underlying cause?
Make sure that ground is connected to the lugs at the rear on the luggage compartment . . . not the ones toward the front which are mounted on the fibreglass inner fender.
OK - but does anyone know the anwer to my other questions - why does this work? Was it the same issue I am having, with the misfire at higher RPM? Also regarding the coil, is there a normal replacement other than the $250 one from Ricambi? I found ones that are close that fit a Renault but not quite. Thanks!!
The fact is an extra ground wire is not needed. You only need one ground wire but it must be electrically and mechanically well connected at both ends and or course the wire should not be too thin. If your original ground wire is not up to par then adding a second ground wire (properly done) will compensate for anything that is lacking with the original setup. Sometimes adding a new ground wire may be simpler than getting the old one "right" but either method is correct. If you add a ground wire and it has less resistance than the normal wire it will improve things. That is why it works. You want zero resistance to ground. The bottom line is the ground connection (in any application) must have zero resistance (in reality you can only get really, really close to zero resistance but that is fine). In certain electrical and electronic applications you do NOT want mulitple grounds. That can cause certain problems but that's another story.
Jim, Take a look at your reference sensors and plug extensions, too. If a plug extension is burned, the hole might be so tiny that it is smaller than a pin, and hard to notice at first. I had three burned extensions on my GTBi; they each created a misfire at a different speed -- one from idle to 2000 rpm, one from idle to 3000 rpm, and one at freeway speeds. Go figure. I don't know off of the top of my head where the tach gets its signal, but if it gets it from the digiplex, I would wonder about the engine RPM reference sensor. Just speculating here; let someone else chime in on that. I also second the ground wire thing as described above. - T
As a general rule, I buy wire and connectors at a boat store. The copper is always made of more and finer strands, and is often tinned. The connectors are almost always tinned brass or copper, whereas at auto supply places they are usually just aluminum. I would think that 12 gauge would be plenty for the Digiplexes, but it wouldn't hurt to go heavier.
Hi everyone, So, I tried the ground wire thing and it didn't work, I still have my misfire - Tony, I haven't replaced my plug extensions - but I wouldn't think that it would cause such a consistent misfire (right around 4500 RPM, in any gear, like clockwork). Besides that I have a new-ish overheating problem.. so I'm battling this thing on multiple fronts right now (UGH..) it's very frustrating. So, regarding this issue, I think my next step will be coils - then plug extenders - or whichever is cheaper first.. I'm not sure at this point. By the way - what's the engine RPM reference sensor?? Can you take a pic for me, or explain where it's at? I guess I could replace that too. I hate just throwing parts at problems but I don't know what else to do at this point. BLAH.. what a frustrating weekend.. Jim
Plug extenders are pretty reasonable in price. I saw a set of used ones on ebay today for about $40. Not sure if they are the correct ones for your model or not. Here is the link; http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200228392824&ih=010&category=46098
Hi James, just wondering if you got your misfire sorted? I have the same sort of problem and just wondered what your fix was? Thanks Anthony
Also check the rectifier on the alternator. They can overcharge and cause misfires especially as you mentioned that the tach had a mind of its own
