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Andrew 06-06-2004 01:06 AM

308 QV - gas cutting out
Has anyone ever experienced the problem of the gas cutting out on a 308 when you get to 5000+ RPMs? It isn't a full cutout but just every other second it seems creating a jerking effect.

What would cause this?

Pete04222 06-06-2004 04:45 AM

Without having any knowledge of the car's service history my first thing I'd check would be the fuel filter.

enjoythemusic 06-06-2004 05:47 AM

Re: 308 QV - gas cutting out
Agree with Pete, if you don't know the history i'd carefully empty the tanks from the bottom outlet to make sure no grunge is sitting at the bottom of the tanks.

Install a new fuel filter.

Add fresh fuel and a add bottle of Chevron Techrolene gas additive as this helps clean fuel injectors/etc.

Andrew 06-06-2004 11:37 PM

Re: 308 QV - gas cutting out

Originally Posted by enjoythemusic
Add fresh fuel and a add bottle of Chevron Techrolene gas additive as this helps clean fuel injectors/etc.

The car is an 82 GTS QV so doesn't this car have the Weber carbs?

4kids3fish 06-07-2004 12:16 AM

No. The QV went to 4 valves/cyl to make-up for the big drop in HP with the injection models (mainly due to smog-controls, I understand, not the FI system itself).

95% chance it would be either fuel (not enough) or spark (not strong enough). If it feels more like a couple of plugs mis-firing then it could be fouled plugs or bad leads / distrib cap / etc. Fuel starvation will probably feel more like a flat spot, as multiple cyls will probably drop-out at the same time. Then again it could be just 1 or 2 part-blocked injectors.

Hope this helps ??? :roll:
ps: Try seeing if it changes with a bit less / more throttle (at same rpm). Fuel starvation shouldn't change much with a bit less throttle, while plug misfiring may smooth out (it is easier for the plugs to fire -ie less voltage req'd - at lower manifold pressure ie when you back-off a bit). :nuts:

Sorry, but this means that YOU HAVE TO GO OUT AND DRIVE IT SOME MORE! :green: :green: :green: :green: :green:

enjoythemusic 06-07-2004 08:08 AM


If changing the plugs, i suggest using NKG Iridium IX BPR7EIX and i believe the gap is 26.

PrancingHorse 06-09-2004 10:45 AM

Fuel filter, clean fuel injectors and check the pickup in the fuel tank (assuming it has one). Also most fuel pumps if not all have a small filter on them too...but I'm sure that wouldn't make the difference. Also might want to check the voltage to the pump at idle, hard to do at 5000 rpms, but if its low at idle it would surely be low under load.

senna21 06-10-2004 05:42 PM

Ok. First off let's all hope this is an ignition problem rather than an injection problem. Why because at those RPMs if you injection is cutting out, or running lean, it will be harder to fix and could cause some real problems.

Also everyone lets remember that this is not an electronic ignition we're dealing with. It's a mechanical. Correct me if I'm wrong but it has a Bosh K-Jetronic injection system. Here's a quick explanation of how it works:

"An early fuel-injection system developed by Bosh that uses mechanical means to meter the flow of fuel to an engine based on the amount of air flowing to the motor. A primary component of the system is a hinged air-flap that hangs in the airstream in the engine's intake. As airflow to the engine's cylinders increases (due to increased engine speed) the flap is deflected which allows more fuel to flow into the engine.

An improved version of this system known as the KE-Jetronic system, retains the air flap but incorporates electronic controls and sensors which aid cold starting and produces more precise air/fuel ratios."

Go here for a full overview:

Iím pressed for time but Iíll come back to this post before I reply to any others because you might have a big problem here. Then again you might have a small one. The big one would be one of your injectors isnít giving the cylinder enough fuel. Notice I said enough. Weíll hope that if itís an injector itís cutting out and not starving the cylinder. If itís not getting any fuel no big deal. If itís not getting enough itís running lean and that can mean youíre burning a hole in either your piston, rings, cylinder wall, or all of the fore mentioned. Or it could be the AFM isnít operating properly and is giving the ECU the wrong signal and therefore the wrong amount of fuel is being delivered.

In short play it safe and donít drive this car hard (if at all) until we get this sorted out. As I said Iím hoping itís ignition and youíre just not getting enough spark to one of your plugs.

When was the last time this car had a tune up? New plugs, plug wires, cap, rotors, ectÖ?

senna21 06-17-2004 03:28 PM

250GTO I haven't forgotten about this problem. I'm looking for an article regarding adding an extra ground wire for the Digiplex(s) located in the trunk.

senna21 06-17-2004 05:16 PM

Iím an idiot. Itís located in the tech section. This would be the first thing I would do to this car. Then test it. I doubt it will fix it but it might and it should be done regardless.

This excerpt is from the old FAF "Ferrari Owners Survivors Manual" circa mid 80's that was in their parts catalogue and had assorted technical tips.

"Why Do Dinoplex units Fail?"

"The Marelli dinoplex unit is an extremely high voltage output device that performs excellently most of the time. Its only fault is it seems to be very sensitive to high input voltage. Most problems seem to occur soon after a dead battery has been jump started. Problems can also occur if the car has been sitting long enough for the battery to drain down, when the car does start, the alternator puts out high current and voltage and sometimes the regulator apparently doesn't catch the over-voltage situation soon enough to prevent damage to the Dinoplex internal circuitry. Because of this apparent sensitivity to high voltage surges from either a jump start battery and alternator or from the cars own alternator, we strongly recommend that you keep the battery fully charged. Thus, if your car sits for long periods use a charger, after disconnecting the battery from the car, before starting."

Does this sound like your car? If the Dinoplexs/Digiplexs have failed the car may not be developing enough spark.

Andrew 06-17-2004 10:48 PM

Hummm :oops: I guess I should remember what articles I've published.

Anyways. It doesn't hurt to try this but I think it is the fuel filter. It only starting doing it in 3rd and 4th really.

Cosmic Artifact 07-05-2005 04:55 PM

i recently had this similar problem on an 85 '308 QV' and after replacing the fuel filter and blowing out all the lines ect...

the problem was in the 'large external injector (black)' sitting just below the (Equalizer valve/Fuel pressure regulator) see pic

there is a small mesh screen inside the end without the hose lead trailing off of it... remove that screen and place a small 'lawnmower style' inline fuel filter between the regulator and the injector. Thats what i did and shes run like a champ ever since. The inline filter was added later as a precaution because afterall the screen did provide a purpose keeping any remaining trash out of the hat. but it did'nt serve well ;)

Another good idea may be to get a can of {BG In-Force} or {PBlaster} and spray just a very small amout down inside the little hole where you adjust your fuel mixture on the jet-tronic unit, then give 2 or 3 full open swings on the air door {"large round object the air filter sits on" :D} but be easy and slow watching the door rise back up and make sure it glides up smoothly with even speed, and does not stick in places returning to the closed position.

it works wonders on clearing the throat out on some of the stubborn distribution units...

the small hole is in this general area an may be capped off.

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