81 308GTSi Backfiring and Popping

PLEASE HELP! My car was running perfect a couple of months ago. 6 months ago I replaced my plug wires and plugs along with cleaning my distributer; water pump, air filter, oil, etc.. Then just several weeks back I heard a popping sound which got worse to backfiring. I then checked out my extenders and replaced all of them along with new plugs once again. The problem seemed to have gone away. It ran great when it was cold, then after I drove it for a while, it began to pop a bit at idle or a real slow speeds. I then double check my gaps and connections thinking this must be an ignition problem. The car still did the slight backfiring when hot. So my next thought it my be the fuel pump or perhaps my injectors. I don't know? Well just recently as of a few days ago, the popping has evolved to major backfiring, and it feels like it is running on 4-6 cylinders, even when cold now. I am thinking now this could be one of my coils gone bad or perhaps both. Please Help, I am stupid Ferrari 101. I appreciate all or any responses. Thanks!!! Aris

Hi Aris,

Welcome to Ferrari-Talk.

Certianly more than one thing can cause the symptoms you describe, but there are quie a few basics that should be covered first.

Have you checked the wiring harness connections to the Digiplex units, and upgraded their ground wire connections? Loose wires & bad, corroded grounds to the Digiplexs are a well known source of erratic ignition problems.

Regards, JRV

Have you verified that the plug wires are installed in the correct firing order? Next, if the problem occurs at idle too, using plastic plug wire pliers, pull the plug wires off one cylinder at a time to locate which one is causing the problem. As each wire is removed, a noticeable loss of engine rpm should occur. If pulling a wire off one cylinder does not affect engine speed, that's the problem cylinder.

Thanks JRV and Bill... I checked the wiring harness and grounds near the Digiplex and there is very little corrosion, perhaps just a slight at the connectors. As for the firing order Bill, it's all right. Since the car as of now is missing spiratically, I did not bother pulling each wire off, in fact, I am almost afraid to start it with the increased backfiring. So today, since I live in FL, nice day, I took my dist. cap off and noticed my points were burned and worn down badly. It looks as though I need some new caps for sure. I slightly sanded them down a bit but they still look bad. I am going to place them back on and give the car a turn to see if it helps a little. I will get back soon, doing it now, please get back with a post. Do you know where I can get some inexpensive new caps in the meantime? This still might not be the problem. Thanks!!! Aris

Hi Aris,

I'm not aware of quality aftermarket caps.

How did the cleaning work out?

Regards, JRV

Hey JRV, cleaning was what I expected, clean but still burn marks.. is this normal? Started it up and I had low pressure, like 4-6 cyls. I ran it until the high rev kicked off. It started backfiring. Didn't help the problem. I noticed the sound was very weak while also noticing the tach reading high rpms, but no strong sound or power like usual. At start up it was showing 5000 then kicked down to the 2500-2800, but the high rev sound was absolutely not there. The choke then went off, I steped on the throttle to give it a little gas, then the tach would shoot straight up fast to 5000-6000 rpm but had no type of power. I shut it off, A long day, but not too much progress. I cleaned around the harness also and the ground like you were talking about, but that part was relatively clean. I was to hope it was something simple, but I am getting a bit aggrivated. Probably still the distributer caps for sure plus who knows. I'd hate to take the car in for service at this point, normally I fix all of the problems because I like to do it for one, and it saves me thousands. What do ya think???????? A Coil? What's Next? Oh, by the way where are those 3 electrmagnetic sensors on this car? Could that be part of the problem?

Hi Aris,

The 3 pick-up sensors are around the bell housing in relation to the flywheel, 1 by the starter, 2 on the back portion of the bellhousing.

The way to isolate the problem is to first determine if one or both banks are missfiring. This can be done by pulling each coil wire in turn while the engine is running to see what effect it has. The problem with the early systems from a diagnostic point of view, is that there are no tests for the Digiplexs themselves, so testing is done by a careful, methodical process of elimination. If the problem is isolated to one bank, that must be determined first. If both banks are erratic that needs to be known.

Regards, JRV

Hi JRV, Ok, I tried to keep the car running as much as I could I had it about 4500rpm. Took off the 1 coil cable and the car died. I did the same with the other and the car just shut off also. The car would not run either way with only one coil connected. So we are getting somewhere right?HA! PLease Help, you seem to know this car better than me. Next? Thanks for the locations on the 3 sensors! Aris

Oh, when the car died at both trys it left a major backfire on each time. Aris

Factory Marellis dist. caps are available from the Ferrari Owner's Site (Ferrari UK) for around $225(!) which is the same as the currently available reproductions, which I have heard some have had problems with last summer.