308QV Ignition Problem--I'm Stumped

Dave, I have a similar problem which my mechanic and I think is the fuel pump and he has fixed 6 similar problems in the last year by replacing the pump.

He said it was unusual but may be an age thing where the pumps have gotten to the stage where they are drawing too much current due to imminent failure and mine comes back to normal when I swap the relays over (I swap the window winder motor relay with the fuel pump relay) because the fuel pump relay is way too hot.

About to put the car in for a service and have this problem fixed, as you say, below ~3000 rpm the car feels like one bank is shut down and then from 3000 on it bursts back to normal

 

With respect to the fuel system, I'll defer to a Kjet expert. You definitely need to narrow the issue to fuel or ignition, though it sounds ignition related.

With respect to the ignition, there are a few things that could be an issue that you might not have caught yet.

Clean/tighen every connector between the crank sensors and the digiplexes.

Add an extra ground strap to each digiplex.

I am always highly suspicious of the crank sensors because they can be intermittant. Even if they seem OK when you check DC resistance, they can be flaky as they get warm. Check them both hot and stone cold.

Birdman

 

Sounds like a fuel problem. The fact that it seesm to get better under acceleration and that all 8 spark plugs seem to be firing.
Is there any black smoke?
To aid in diagnostics you can run jumpers to the cold start injector with a push button from the cockpit and fire while it is missing. If there is an improvment you can begin to investigate a lean condition.
Another quick thing to try is something to put in the gas tank like fuel injector cleaner (Techeron is supposed to be good) or gas dryer.
Could you have picked-up a bad tank of gas?

I don't think it is a clogged fuel filter because it would run worse as fuel requirements increased.

Mark

 

I would agree, if the plugs are all firing, I'd be checking for fuel problems. Put fuel pressure gauges on it and see if the WUR is putting out correct pressures.
Before that though, I'd add the Techron fuel cleaner and add gas to mix it up well , then run the crap out of it at high rpm,to see if that will dislodge any crud in the fuel system.
Ferraris love to be driven, the more you drive, the better they run, this time of year that isn't always possible.

 

Mark, I suspected the above so tried FI additive which didn't help but always worth a try and a lot cheaper than fuel pump, also I think a bad lot of fuel would bore noticable with the car running very ragged from my experiences of picking up a bad load of fuel.

 

My crank sensors checked out ok but I got a intermitant miss when warm. Turned out they were the last in a list of parts I replaced before I got it right. Don't overlook where the plug wire boot connects to the plug extender I have had some problems there even with almost new boots.

Larry

 

If you want to test your fuel system call me, It is too detailed to type here and needs to be more interactive. Might be that I type too slow? Anyway I can run you through the tests you need to do.

Larry Fletcher
251-929-3771

 

Sounds like fuel.

I cannot remember if the 85 had gone to the frequency valve and O2 sensor system (some of the late 85s did, and all of the 86 forward I think), but if so, it may be the protection relays and/or fuse on the FI ECU board in the right rear of the trunk; take the big relay with the fuse on top off and check the fuse, them shake the relay to see if it rattles. Rattle = bad. It is a common Bosch part. Ask me how I know.

Good luck and let us know.

 

I have had these exact symptoms many times before on my Audi's with Bosch CIS / frequency valve FI systems. I would strongly suspect the frequency valve itself --- they go bad alot. You'll find this electrovalve located inline with the inlet fuel supply line going into the fuel distributor --- the component will look similar to an electronic fuel injector and will likely be mounted on the fuel distributor body somewhere. And, oh by the way, of course, they are not cheap....

 

Oops... ignore all of what I've said above...308QV does not have a frequency valve in the FI system.

 

It's possible that you may have corrected the original electrical problem but, if you didn't replace the plugs, one or more could have glazed over during the time you ran the car while it was missing. If so, you may be getting good spark to the plugs but the glazed one(s) wouldn't fire anyway. This happened a couple of times with an '85 308 I had. Replacing the plugs, after fixing the original electrical glitch, solved the problem.

 

Running poorly at low RPM and fine at higher RPM is a symptom of a vacuum leak. Have you checked for this?

Just a thought.

 

My 85' 308qv and I think the 84'qv's both HAVE the Frequency Valve.
The 83'qv is different I believe.

 

I subscribe to this, I had a problem last year, very similar, the problem was crappy fuel. I used Wynns fuel cleaner, Techron is not available in UK.
Problem solved.
Give it a go, its a cheap option with no risk and real payback if it works.

 

Dakharris wrote :
"What is the inline unit between the pump and the filter?"

I think that is the fuel accumulator, it holds fuel pressure after the car is shutoff, so that later, it will restart faster without having to re- pressurize the entire fuel system.

 

Dave:
If your pump is making a lot of noise a likely cause is the fuel strainer inside of the fuel tank. If this gets clogged the fuel pump will cavitate and send bubbles into the system and it will make much more noise than normal. When it makes noise, the pump is on a path to self-destruction. You can drain the fuel, remove the strainer & clean it. There have been several write-ups on draining the tanks, so the archive should have something. I have some pictures of the strainer somewhere.

If you wanted to check your FI system further, you should probably hook-up a CIS tester.

You can check many FI system electrical components with a VOM meter and the step-by-step instructions here in http://ferrari.cdyn.com/ferrari_docs/328_bulletins.pdf
See Service Bulletin 80-29
Larry is a noted expert for the Bosch FI, if he offers, I would call him.

Mark

 

Anyone recommend checking the Lambda relay on the Jetronic fuel injection computer?

 

I had this same problem... at idle, no load, car runs just fine even gunning it to redline. Turns out I had bad fuel. Some STP fuel additive corrected the problem. I also thought it was the pump or filter. But was told when they go they just go. The plug extenders were also on my suspect list. Similar problem at higher RPM. I ended up having a bad one that was starting to break down on the inside.

 

This post sound exactly like my problem with my 85 Mondial QV over a year ago, I tried to get the problem to follow a part, switching out part from front to back bank, then moved on to fuel pump, power, wire harness.... on and on. As it turned out it was the rotor that went bad. The crack was so small that I over looked it when I took them off the first few times. I did not think much about it as they were fairly new at the time. I hope that this works on your car, good luck.

 

Check the digiplex earths again, or run fresh ones. I've come across a very similar problem before, and it's a nightmare to diagnose as it's tricky to produce a sufficient load on the engine to induce the misfire whilst not driving. If Pulling away and/or loading the engine by accelerating produces the fault then it's more likely to be an ignition fault than a fuel one. Anyone with a standard engine analyser should be able to tell straight away if this is the case, just by looking at the spark KV's in scope format. It's a lot cheaper to pay for a half-hour diagnosis with an an engine analyser than it is to start replacing fuel pumps etc, and looking at the screen will also indicate primary or secondary ignition fault.

 

I probably shold know this, and since I don't I think it would be a good time to ask, What is a Digi Plex? and where is it. If the car is running well should I change or increase the ground wire?

My 85 308 I had out over the weekend and noticed it wasn't coming up to full tempature and wasnt running all that great below 4,000, not missing more like it was holding back. The water temp gauge is only going up about half way from 0 to 210 and the oil gauge isn't as high either. I haven't put the wifes meat thermometer in the expansion tank yet, I am guessing my thermostats is stuck open and will need to be change.

I added 13 gallons of Shell premium, and noticed it ran better on the way home? Did the engine warm up to where it ran better or was it newer fuel?