Alfa 75 3.0 V6 Bogging on Acceleration & Slow to Start



Cheers pal


As the next test, I would suggest hooking up a fuel pressure gauge

As for finding the specs for your system, that’s on you

I may be wrong, but I believe your car uses a Bosch L-Jetronic fuel injection system

here’s an interesting website for you to check out

To anybody reading this . . . it’s not spam. I’m simply trying to help the op

Here’s a book I recommend, a book which I used to own decades ago. I seem to remember it actually has specs, function description and troubleshooting

Another possibility comes to mind . . . your volume air flow meter. In any case, both the website and the book should show you how to do some testing


I appreciate your help. I’ll carry out a fuel pressure test in a couple days


you’re welcome

How are you going to hook up your gauge?

Unless I’m mistaken, you’ll have to tee in using adapters


It seems like you are doing all the right stuff. Your compression test results should give you a lot of hope you’ll soon have a smooth running machine there. I’m assuming you are checking for diagnostic codes from the computer system and not finding any, right? I can see why you want to avoid the 100 pound expense for new wires, given they appear from your testing to be ok. Maybe as a compromise just remove and clean them in soap and water, then inspect the insulation carefully on the bench under good lighting. I found a problem on one the my truck’s HV wires doing that. I had a clue though, a noticeable misfire, and I heard a slight zap sound now and then. A small crack and signs of arc’ing was visible on that wire as viewed on the test bench , but barely. I was able to repair the trouble spot using some HV electrical tape rather than replacing the wire, which solved the zapping and the resultant misfire.

My old Rabbit had the Bosch K-Jetronic fuel injection. Very sensitive to fuel quality. For comparison, I’ve never had a fuel injection problem on my Corolla in 25 years, but on the Rabbit I had to fix something w/ that every 6-9 months after the car aged to the 6 year mark. When that system clogged up – due to grit in the fuel – the symptom was lack of power. I’d press on the accel pedal at 25 mph, press it all the way to the floor, maybe I’d increase speed to 26 mph … lol … When that happened I had to disassemble the fuel distributor into its various parts and clean them all up to get it to run well again. I never had a problem with the injectors clogging, but I did have to replace the injector o-rings a few times. The L-Jetronic is a different beast though, but if you can find instructions on how to disassemble & clean it out, that’s probably something to try. On the Rabbit is was very easy to clog the system as part of a fuel filter change ironically. Somehow dirty fuel from the old filter would get past during the change-out.

When I read your comment

The car runs well for a minute or so, then will run poorly for a min or so. When running poorly, there is a lack in power, fluctuating idle, splutter when reving (sometimes with backfire), occasional stalling.”

my first thought is a problem with the ignition system that generates the spark. That’s often heat sensitive and intermittent. On my Rabbit it was just a points and single coil system. The only problem I ever had was a cracked coil that made it stall if I ran over a puddle of water. The crack was on the underside and so tiny it was nearly impossible to see. For the Rabbit, it was a big coil on the firewall, not the small coils more common now that are located inside the distributor. If you have a big coil like that, remove it, clean it up, and inspect it on the bench under good lighting & using a magnifying glass for really tiny cracks. If you have a coil and ignition module inside the distributor, which senses the distributor shaft turning to synch up with the crankshaft, that could be the problem.

I should add that o’scope testing of the ignition system is very helpful to diagnose an ignition system problem. That’s what I’d do first if I had the same symptoms with one of my cars. If you lack the equipment or knowledge how to do it, at some point your best bet may be to have to ask a shop do an o’scope analysis.

Edit: One more idea, do an EGR test. You may have an EGR valve that is sticking open.


There is a fuel line running from the main fuel rail to a cold start injector. I will hook up to that



The car has no diagnostics system.
As for the fuel system, I’ve drained the tank and put new quality fuel in. I’ll check the fuel pressure next week.
I’m not sure the car has an EGR valve


I carried out a fuel pressure test this weekend. Pressure rises to 35psi with ignition on and MAF sensor opened.
With the engine started, pressure remains at a steady 25psi at idle, and holds steady with revs.
Disconnecting the vacuum line from the fuel pressure regulator causes pressure to jump up to a steady 35psi.

I mentioned earlier that the car runs poorly every so often. Well it seems to be after the car has been running for 10/15 minutes, the fuel pressure starts to decline, followed by an increasing in volume whine from the fuel pump. It declines from 25psi to 20, then 15, then 10 followed by misfires and boggy acceleration and then finally stalls. After the stall the pressure drops to zero.
With the engine stopped, I turned the ignition back on, opened the MAF and the pressure jumped straight up to 35psi. I started the engine and it ran perfectly fine for about 15 minutes. I then shut it off.

I should add that the fuel pump is brand new, the fuel filter was changed a few months ago and most of the old fuel was drained out (car been sat for 5 years) and replaced with 10L of fresh fuel.

Any ideas about this strange behaviour?


Jack , this has been said before . The Alfa brand was not sold in the US for a long time so mechanics with knowledge of them are few . Can’t you find a mechanic near you to solve the problems you have. Plus the fact that it sat for 5 years I hope you got it cheap.


The pictures make me believe he’s in Europe, probably Great Britain

Those are standard european size plates, and the steering wheel is on the right side

I bet there ARE a few shops familiar with that car nearer to his house


When the fuel pressure drops, have you verified that the fuel pump power and ground are still correct?

Did you install a reputable brand fuel pump and filter?

As far as fuel pressure specs, do you even know what the specs are for your vehicle?

I’m not familiar with Alfa fuel injection . . . as I said earlier, you appear to have Bosch L-Jetronic . . . but 25psi at idle sounds somewhat low. Might be within normal parameters, but it’s far lower than anything I’m working on currently

Have you verified with a wiring diagram and a multimter, that the fuel pump relay is working properly, and not conking out when the fuel pressure drops?

That fuel pump you replaced . . . is it external or internal?

If it’s internal, did you also replace the “sock” filter?

How did you go about draining “most of the old fuel” . . . ?


As I’ve said before, I’m just after general advice. Forget it’s an alfa. I’ve also posted on the alfa forum.

Power and ground I’ve not checked. I’ll do that. And yes a genuine EXTERNAL Bosch fuel pump was fitted. The old fuel pump was also whining, which I why I replaced it.
35psi is what should be measured with the MAF sensor open with ignition on, according to specs. I’m not sure if 25psi at idle is good.

Drained out ‘most of the old fuel’ by using a syphen pump


When this happens have you removed the gas cap to see if a vacuum has developed and is causing the problem? It could be a fault in the gas tank venting system.


Actually the opposite happened. We ran the car for about a minute, then when I took the filler cap off, the cap got blown out, almost out of my hands. This occurred before the pressure started to drop however


Forgive me, but what you’re saying is confusing

On the one hand you said 35psi with ignition on and MAF sensor open is within specs . . . which makes me think you’ve got some kind of a service manual

Yet you don’t know if 25psi at idle is within specs

Just where are you getting your technical information?

Do you have a factory service manual, or that Bosch book I gave you the link for?

Fuel pressure which is too low can certainly cause driveability problems

I suggest you get your hands on some information which will give you exact specs

I hope you’re in contact with somebody local who is more familiar with Alfas


Why , that fact is relevant to any useful response . This vehicle sat for 5 years , you have been spinning your wheels for about 7 months . I just don’t understand why you can’t find local help to put this thing on the road.


That’s correct that the rail fuel pressure jumps about 10 psi at idle when you remove the intake manifold vacuum source to the pressure regulator. So something is right at least. The reason that happens is b/c it’s necessary to keep the pressure difference between the rail and the intake manifold constant, the manifold vacuum pressure is about -20 in Hg, and - 30 in Hg is -15 psi, so -20 in Hg is -10 psi. You should also check that with the vacuum line connected the fuel rail pressure raises quickly when you bump the accelerator, then falls again when you release the accelerator. That shows the pump and fuel pressure regulator are correctly responding to the dynamic changes in the intake manifold vacuum as the throttle position changes.

I’m not sure why the MAF has any effect on the fuel pressure. That must be something unique to that system, maybe signals the electronics you want to do a pressure test.

Can’t speak to whether 35 psi is the correct regulated fuel pressure at idle, the manual will tell you that. My Corolla’s is 38 psi as I recall, so 35 psi seems in the game. However the fuel pressure almost certainly shouldn’t fall like that as the engine warms up. It should hold steady as a rock. Fuel delivery in modern electronic injected engines is regulated by injector pulse width, not fuel pressure. A 1988 Alfa probably uses that method too. I think once you figure the unexpected fuel pressure drop out you’ll be over the main hurdle.

So what’s causing the fuel pressure drop? Fuel pump is lazy as it heats up, electrical power to fuel pump dropping, fuel flow restriction. My guess – I’ve had some experience with Bosch FI, the CIS version tho – is the second one, there’s a problem with the electrical power being delivered to the fuel pump. Something is heating up and causing a higher resistatnce connection somewhere between the battery and the fuel pump’s electrical lead. More likely this is occurring either at the fuel pump’s electrical connector, or the fuel pump relay. Suggest to back-probe the fuel pump voltage at the fuel pump connecter as you repeat the above experiment. I’m guessing you’ll see the voltage dropping along with the fuel pressure.

One other idea, the fuel pressure regulator is failing. I believe you said above you checked that it holds vacuum and there’s no fuel in the vacuum line, so I doubt that’s the reason, but something to keep in mind for backup.


Aren’t you making wild assumptions?

Just because you know what your fuel pressure is supposed to be, doesn’t mean it’s a good baseline for this Alfa

I’ve worked on vehicles that have normal operating pressures far higher than your Corolla. And they’re common vehicles


I think you mean “inches” not “mm.”


Yes, I’ll correct above. Brain freeze … lol …

Note to self: 30 in Hg = 760 mm Hg