Alfa Romeo Forums banner
1 - 20 of 25 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter · #1 ·
My 1988 Alfa 75 3.0 V6 seems to be bogging under acceleration. After reaching operating temperature, it can run fine for a few minutes (plenty of power), but then it frequently has a few bad minutes where it has no power, jerks and hesitates with acceleration and sometimes backfires with a pop. It seems to run poorly after a few minutes of driving.
The car hasn’t been run properly in about 7 years. I had an issue with the fuel injector o-rings leaking air, causing a misfire. I’ve since replaced these and it’s now running on all 6 cylinders. (before I replaced the o-rings, the bogging issue was significantly worse).

Another issue is that the car is VERY slow to start – turn the engine for 10 seconds, stop, then try again after a few seconds and immediately almost comes to life but then back to just cranking. Can take 20 seconds of turning engine before it eventually comes to life.

Idle is okay, but every so often runs rough for a few seconds. This occurs during the warmup and then again after the car has been running for a while.


Any ideas would be appreciated!

Jack
 

Attachments

·
Registered
Joined
·
265 Posts
I'd check the fuel pump pressure and fuel filter.

When the filter gets clogged the symptoms can be as you describe to... fuel pressure is ok and will idle fine but no power as it can't get the flow.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #3 ·
I'd check the fuel pump pressure and fuel filter.

When the filter gets clogged the symptoms can be as you describe to... fuel pressure is ok and will idle fine but no power as it can't get the flow.
The fuel pump and filter are brand new. Will a fuel pressure test be sufficient?
 

·
Registered
Joined
·
166 Posts
There is a fuel relay on the right side firewall in the engine bay that has a habit of giving up. I have no idea if it could result in the symptoms You describe nor if it can get iffy or just dies. But if you have a replacement relay it is an easy thing to test...
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #5 ·
There is a fuel relay on the right side firewall in the engine bay that has a habit of giving up. I have no idea if it could result in the symptoms You describe nor if it can get iffy or just dies. But if you have a replacement relay it is an easy thing to test...
Do these cars prime the fuel system when the ignition is turned to on (not start)? I know on most cars you can hear the fuel pump prime when you turn the ignition on, however no noise from my alfa. Could this be the issue?
 

·
Moderator
2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
Joined
·
17,388 Posts
"Another issue is that the car is VERY slow to start – turn the engine for 10 seconds, stop, then try again after a few seconds and immediately almost comes to life but then back to just cranking. Can take 20 seconds of turning engine before it eventually comes to life"

Check the functioning of the cold start injector at the back of the intake plenum.

Most Milanos (75) start right off immediately when cold and foot off the throttle, but take several cranks with a slight opening of the throttle when warm. And, many of these cars will start from cold even if the cold start injector is disconnected, but some won't without a good deal of cranking, maybe as yours.

Our Milano starts immediately from cold when the key is turned and starter engaged. The starter doesn't even get to rotate more than a turn or two. When warm, it does take a little longer to start. This is normal.

Also, if you haven't already done this, check the condition of the cap, rotor, and plugs. If they are old and contaminated, the engine can have a tough time starting. I use the NGK Iridium plugs in all my Alfas and they are flawless IIHO. And, run FI cleaner once in a while for a few tank fillings to help keep the fuel system and valves clean. Has worked for my Alfas for years.
 

·
Registered
Joined
·
265 Posts
Hi jack.

Check it's not losing fuel pressure (so more leaks). The rail should remain pressurized after shutdown. The fuel is pump engagement is triggered both from the crank sensor and the air flow meter "flapper opening"

Try bypassing and connecting power directly to the fuel pump as a first step. The AFM might need a cleanup of it's internals... Is the plastic top secure? I'd prise it off and check it's all clean and not got any corrosion or and moving as it should when cranking over. (re-secure it with some silicon once you're sorted)
 

·
Registered
Joined
·
180 Posts
If it turns out to be a fuel delivery issue and it's not one of the usual suspects, check the two steel fuel lines that run across rear of the car from the fuel pump to the fuel filter area. My car had the return totally clogged with corrosion and the supply line was badly restricted. Oddly enough, the rear to front lines are plastic and they were fine. Fwiw, my car had been off the road for several years prior to my purchase.

Sent from my Nexus 5X using Tapatalk
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #12 ·
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. 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.

Any ideas about this strange behaviour?
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #13 ·
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.

Also, after the car has been running for a while (and starts to run poorly with decreasing fuel pressure), the fuel pump begins to whine louder and louder
 

·
Moderator
1991 164L
Joined
·
27,898 Posts
Suspect fuel tank filter sock 60523429

First thing that comes to my mind about fuel pump whining is you have a clogged 60523429 ** filter sock in bottom of fuel tank. It is the big fuel outlet fitting that supply hose going to inlet of fuel pump is attached. The filter sock is fine mesh and could be glazed over from rancid fuel.

Fuel pressure seems low as my 164 system pressure is closer to 40-45 psi.

Second thing is possible false air from crack in intake's big black hose between air flow meter on air cleaner and throttle body on intake plenum.

If motor mounts or air cleaner mounts worn/broken and engine moves a lot on acceleration it can open up crack in hose.

** FISPA 316002 OLD AR # 11911320260200 WRENCH/SOCKET SIZE TO REMOVE IS 32MM
 

Attachments

·
Registered
Joined
·
25 Posts
Discussion Starter · #16 ·
Thanks for the reply Steve. I’ve had a look inside the tank, and that mesh looks clean. I’ve not taken it out yet though.
Do these cars have an in tank submerged pump? As well as the main
 

·
Moderator
1991 164L
Joined
·
27,898 Posts
Thanks for the reply Steve. I’ve had a look inside the tank, and that mesh looks clean. I’ve not taken it out yet though.
Do these cars have an in tank submerged pump? As well as the main
No internal pump in GTV6 or Milano. Gravity feed through that filter sock.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #19 ·
Back again. Issue still not solved. Any ideas would be appreciated

Current Issue: Loud whining fuel pump (brand new), and engine bogging on acceleration after about 10 minutes of light driving.

Recent Work Done:
Suspected a blockage in the fuel tank, so we began to drain it from the main outlet (gravity fed at the bottom of the tank), and noticed that after a few seconds of draining, it went from full flow to a slow trickle, almost stopping. The tank had at least 10ltrs in. We decided that the intank mesh filter (you mentioned Steve) must be blocked so we gave it a knock and the fuel started flowing again. We decided that this must be the cause of our poor running, and the cause of the whining fuel pump.
We removed this filter and instead installed a small inline filter. Fuel now flowing freely out the tank by gravity - no blockages before the fuel pump. Just been for a test drive, and the fuel pump is still whining (???) and engine bogging after about 10 minutes.

What could be going wrong, and most importantly, why is our brand new fuel pump still whining?! This has to be a clue to our running issue

We have also checked the fuel pump supply voltage - all good
 
1 - 20 of 25 Posts
Top