F40 acceleration problems

I would spend some time going over the ignition system in your car. The only mention I see of ignition troubleshooting in your post is that you regapped your plugs. On a 20+ year old very high performance car like the F40, with an older traditional ignition system that uses HT wires, it should be one of the early suspects for poor running.

You should go through the wires, and coils, looking for cracks, carbon spots, or other points of distress. Also measure the resistance of each of the wires to look for internal breakdowns. Measure the resistance of each coil as well. Put a timing light on each HT wire as the engine is running and check that it's flashing smoothly & regularly.

If possible, and parts are available, I'd go ahead & replace the wires & coil on one bank of the engine and see if the issue improves, then do the other.

Caveat: I am not a specialist on the F40 itself or its ignition system (I own a 550 Maranello), however I do know a few things about ignitions and boosted cars in general, and all boosted cars are VERY demanding on an ignition system.

Your symptoms are typical of a weak spark that is being blown out at the onset of boost. This is the point of most stress for the engine and ignition, as you are looking for peak torque from the engine, and cylinder pressures have just dramatically increased with the turbochargers coming in and providing more air. A weak ignition cannot meet this demand.

I can't say that the ignition is the root cause of your problem, but I can say that on a 20+ year old turbocharged car like the F40, it probably does need attention.

 

You said, that You just checked and gaped the spark plugs. REPLACE THEM!!!! Sometimes they get a problem and need to be replaced (don´t ask, i replaced a lot of spark plugs on our F40...).

After that, check the sensors at the camshaft! They tend to rust away, the rev sensor generally makes no problem, but the phase sensors (again, don´t ask, i replaced 2 sets on the F40 and even more on the GTO...).

And replace the exhaust with an original one! You have different backpressure and the mapping is just not made for this!

Wish You luck to solve the problems.

 

Coils, injectors, fuel filter (As dumb as that sounds) Boost leak

 

The details I can find online about the F40's ignition is that you have twin, 2 tower coilpacks per bank and the 2 HT leads from each coilpack go to adjacent cylinders, which leads me to believe you may not have a waste spark ignition, depending of course, on the actual firing order of the engine and its cylinder numbering. Is the firing order the typical Ferrari V8 order of 1-5-3-7-4-8-2-6, and cylinder numbering (looking from flywheel) is 1-4 on the right bank, and 5-8 on left, with 1 & 8 being furthest from the flywheel and 4 & 5 being closest to the flywheel?

In the interest of eliminating the ignition as the issue, I might pick up some cheap coils & HT leads just for testing, and see how they work out. Since you mentioned a possibly bad ignitor, I'm assuming they're external, and it sounds like you already know your way around an ignition, so I won't try to spoon feed you any of the basics

If it were me, I'd probably try the temporary replacement ignition using Ford coilpacks and leads and see how it works. What's key is whether the existing setup is running in waste spark or not, as that will determine what type of temporary coilpacks you can try. (You could, of course, still try a pair of 4 tower Ford coilpacks on each bank, and only use 2 of the towers and shove silicone plugs into the "complementary" towers. Two of these and four leads would probably only set you back a hundred bucks or so.

 

It seems unlikely to have an ignition problem due to malfunctioning coils, plugs or wires if the car runs at full boost and RPM, but not at just .8 bar and 4000 rpm. It sounds more like a problem at the onset of boost, and I'd wonder if the second set of injectors is not starting to fire properly. The basics are always fuel, spark and air, and you sure seem to have looked at these, but do all 16 injectors have good flow rates and spray patterns? As you also note I'd want to be sure the EEPROM is correct, but I can't help there.

The mystery to me is that the car makes power at 1.5 bar and 7500 rpm as you describe it, but not at 0.8 bar and 4000 rpm. That tells me there is enough fuel and spark capacity, just an issue at the onset of boost. I'd want to put a wide band O2 sensor in the exhaust to see if there is a momentary lean condition that precedes the misfire.

 

I doubt the problem will be with the injectors or any of the fuel delivery system, because the engine can make full boost / power at high revs, where the demand on the fuel system is greatest.

I also doubt the problem is in the ignition components either, as the greatest load on the ignition system is at high revs / load, and that seems to be ok too.

I'd be focusing on the engine control systems, either the sensors feeding the data to the system, or a poorly remapped ecu. The fact that the problem is repeatable and occours at the same point strongly suggests a control or sensor problem

The previus suggestion of a wideband O2 sensor to check for leanout is good,
In the absence of spare ecu's to test, I would also try to plot the boost / vs revs and ignition timing vs revs to see if that matches the factory specs. That should give you a clue if the ECU has been remapped.

Has anything been done to the turbos ? Different a/r ratio, housings, wastegate etc?

 

I couldn't tell from the 1st diagram below if the engine had waste spark ignition, as it was difficult to follow each of the leads, however if one of your coilpacks is feeding cyl's 1&4 and the other is feeding 2&3, then it's certainly waste spark. The only thing that still gives me doubt is the ignitor module itself in the 2nd pic below. This "module" is nothing more than 2 Bosch 2 channel ignitors packaged on a heatsink, however according to the parts list, the engine requires 2 of these modules (1 for each bank), which would indicate to me, there's a need for 4 separate ignition outputs per bank, UNLESS as you say, the ECU on each side is only outputting 2 channels, and they've paralleled these ignitors at their inputs, in order to get longer dwell and more current capability at the output? I've done this on my bench simulator for a 550 ignition and it does produce a hotter spark.

But if you're sure it's waste spark, then it'll only take a single 4 tower coilpack to feed each bank, and a standard Ford V8 EDIS/coilpack setup from any of their 90's cars should work fine, temporarily, and shouldn't cost more than $100 to $125 total. Cheap test and probably would be a better ignition than what's on there now.

I'd also pick up a few of those Bosch 2 channel ignitors (0 227 100 200) just to be safe, but I'm sure you've already thought of that.

This would be a fun car to upgrade to a COP ignition and possibly a CDI type COP setup, and it would clean up the engine bay a lot Not the sort of thing for a purist, but if your owner is a hotrodder...... If you're interested, drop me a PM; my V12 ignitions are running on 10-12 550's now (one of which is tracked regularly over in the UK), and I've helped a couple of owners sort out their 348/355 COP setups.
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Someone else might chime in on this, but way back when these came out, installing an exhaust without enough back pressure would spool turbos too fast for the engine mapping and the exact problem you describe would occur. There was some black art retuning available which overcame the problem. Similar issues can be replicated on porsche TTs for similar reasons, electronic remaps cure those.

 

So far I don't see clearly if it's boost-related or RPM-related. If you creep the revs up at light throttle so you're not coming on the boost at 4000 RPM, does the problem still happen? What about if you're running over 5000 at light throttle and go WOT?

 

When the turbos spool up very quick, showing overboost to the wastegate and computers. The result is a brief very violent shutdown

 

Yep.

Common problem. We ripped our hair out over that back when they came out.

 

is this a PD algorithm/duty cycle controlled waste gate-a-la-USA catalyzed versions...or...is it early NON-cat with 3 "flat" exhaust pipes to rear of car a-la-288GTO..is so, THAT waste gate is THE SAME as a 288, same p/n as I recall...

if this car has a proportional derivative algorithm driving a duty cycle...ANY change in back pressure adversely affect back pressure and the system can't bleed off the faster rate of change in the rate of change of boost ONSET(second derivative) to deal with this, the waste gate must be modified internally. A minor bore from 1/2 to 1mm in a line, etc, etc...
This is NOT a well understood area of modification on these cars and it really is difficult to deal with over the internet without even understanding what is baseline configuration...
perhaps some more detailed pics of the exhaust and turbo stuff? This is a slightly more detailed version of the esteemed shooter's explanation, however, it does really-IMO-applies more or less ONLY to cat versions-regardless of country of delivery, as the "cold bag" section is all that is really different within the "map".

 

Can You see, if the Wastegate was manipulated?

It more or less is set to a specific opening pressure and acts mechanically. Than You have an electric bleeding valve unter the right Airbox. Check this! (A friend brought an F40 with a broken Wastegate and bleeding valve. He had massive problems)

Maybe someone manipulated the wastegate to go around replacing the bleeding vale. The bleeding Valve is easy to check: do You hear a "click" when the ignition turns on/off?

 

Also can be. I just replaced two broken Wastegate Membranes. You can test it by applying pressure to the Wastegate and see, if it leaks. If not, remove the Wastegate completely and check for free movement. DON`T OPEN now as it can destroy the membrane!

Only open if the membrane is split!

Sorry to advice You to check the valve, it is hard to read Your snail-text and remember everything

 

Than open it.

You than will understand the symptoms. The membrane is pushed against a piston and the Wastegate Housing under pressure. When the crack/hole is neither on the piston or Wastegate Housing, You will have a leak. (Hope, You understand what i tryed to describe...)


Picture is from a 288 GTO Wastegate, but it is very similar (GTO is pressurised by exhaust gasses, F40 by charged air)
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