Alfa Romeo Forums banner

1 - 20 of 24 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter #1
Hi all,
I have a 1974 spider and my fuel pressure light flickers at~3200 RPMs and comes steady on at~3500 RPMs under full throttle at higher gears(3-4-5). The car has an oxygen sensor with a kit showing that the engine is actually always running nice and rich even when the light is on. I have changed both the tank and the main fuel filters but the problem is still there.
What gives?
Thanks,
Steve.
 

·
Registered
Joined
·
9,977 Posts
Is your car a 74 with SPICA or an 84 with Bosche injection? I've never heard of someone retro-fitting an O2 sensor to a SPICA injected Alfa.

If it's a 74 The most likely cuprit (if it's not the filters) is a failing supply pump.

If the light is coming on despite fresh filters, then:

1. Check wiring, clean connections and check voltage at the supply pump.

2. Is there rust and setiment in the fuel tank that is clogging the rear filter quickly?

3. Are the hoses (especially the suction side from the tank to supply pump) is good shape and not collapsing?

4. Supply pump should put out a minimum of .5-.6 gallons per minute. The light comes on at 7 psi, but the normal system pressure is more like 10-20 psi. If you check the fuel pressure DO NOT TAKE DEADHEAD READINGS. The pump is capable of putting out very high pressure if deadheaded and could blow a hose off a fitting causing very spectacular results. If you want to check the exact fuel pressure you MUST put a "T" fitting into the system between the supply pump and the injection pump.

My 74 did the same thing last summer. It was a weak supply pump. Does it make "uneven" noise or is it a steady whine? My guess is that if you continue to run it as is, then the light will progressively come on more and the engine will eventually start to stumble from lack of fuel pressure to the injection pump.

You should NOT drive around with a fuel low pressure light even if the engine runs ok. The SPICA pump relies on recirculated fuel to cool the pump. Operation with low fuel pressure can cause premature wear on the injection pump plungers and pistons. BTW, if you're not using a top cylinder lubricant like Marvel Mystery Oil, you should. MMO will supply a bit of lubrication that was lost when we went to unleaded fuel . . . and remember, the SPICA pump was orginally designed as a diesel pump.

The original SPICA supply pumps are no longer available, however, the Bosch supply pump from a Bosch L-jetronic system is a suitable substitute . . . although you'll have to fit spade connectors to the pump, or fit round connectors to the pump supply wiring. In addition, the Bosch supply pump is slightly less in circumference and will require some foam or something to mount in the existing bracket.

One last note. I would not buy a used pump off of Ebay. I bought one from a dismantler called "Dreamcars" and it was defective and they would not refund. $60 down the drain. Bite the bullet and get a new one.

Cheers
RT
 

·
Registered
Joined
·
9 Posts
Discussion Starter #3
Hi and thanks for your reply RT.
The car was restored by the previous owner last year and the fuel hoses look new. Dirt, rust in the tank are possible but not likely since I was told that the tank was cleaned before being reinstalled in the car. I have not checked the voltage at the fuel pump (I will do it tomorow) but the pump sounds even and loud.
I have made a pressure gauge with a T-fitting with a cheap pressure gauge I bought at Home Depot's plumming supply but I am afraid to use it since it was meant for water not gas and if parts of it desolve it may couse internal engine problems (what do you think). Is there a fuel return valve and is it possible that this may be the problem (how do you check?).
I am using Marvel Mystery Oil in the tank already.
Thanks,
Steve.
 

·
Registered
Joined
·
9,977 Posts
I don't think that gas will do any harm to the gauge especially for the short time that you'd have it hooked up. To be sure, put your "T" fitting in the line before the front fuel filter and, as always, keep anything to do with fuel away from any ignition source. With long enough hose there shouldn't be any backflow into the fuel system if you pinch it off before disconnecting and draining. Regular old-style automobile vacuum gauges usually double as fuel pressure gauges, but they usually only go up to 10 psi on the scale (while the supply pump may put out 10-20 psi). Also there are tester gauges for electronic fuel injection systems that read up to about 40 psi. You might use one of those since they're meant to be used with gasoline.

I am not aware of a pressure relief valve in a '74. Some of the later supply supply pumps had 3 fittings (vice 2 like yours), one of which was a pump PRV with a return line to the tank. Fuel pressure is regulated by a restrictor orifice in the outflow fitting of the SPICA injection pump. From that fitting, fuel is returned to the tank and recirculated to cool the injection pump.

I'm still betting that the supply pump is weak.

A proper test of the pump would be to take about 4' of fuel line and connect it to the OUTLET (the fitting farthest forward) on the SPICA injection pump and run the other end into a gallon container (a plastic milk carton would do). Run the supply pump for 1 minute, then measure the output quantity. If it's less than .6 gallons, then the supply pump is not meeting spec. The pump may be capable of putting out good pressure, but if it's weak in flow capacity, then the pressure will drop rapidly when fuel is used out of the line.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #5
Ok RT,
I run the flow test you sugested with the engine off and I got 74 oz=?.58? gallons. Do you think that's close and it may be the sensor itself or should I change the pump.
Also if I run the engine like this for say a month do you think it may damage the SPICA or can the pump just quit?
Thanks,
Steve.
 

·
Registered
Joined
·
9,977 Posts
Hmmm . . . . . . .58 gal is close enough, so it seems the pump is putting out good quantity so that's good news at least for now.

Before going any farther, I'm going to ask a couple of seemingly dumb questions:

1. When you say the fuel pressure light comes on, I assume you're talking about the TOP LEFT red warning light on the center dash and NOT the TOP RIGHT which is the oil pressure light?

2. Have you checked electrical connections clean and tight and that the wire from the gauge to the fuel pressure sending unit (on the front fuel filter) isn't grounding out somewhere when the engine vibration is "just right?" That pressure switch is a grounding OFF/ON switch that operates such that when the pressure is below 7 psi, it provides a ground for the pressure warning light, which then comes on. You could double check that by using a simple test light (one wire to the + battery and the other on the spade terminal on the pressure switch.

3. Turn the ignition on and let the pump build up pressure. How long does it take from key turn to the fuel pressure light to go off (and I'm assuming the battery is not weak or discharged)? Should only take a couple of seconds. When cycling the ignition switch from ON to OFF to ON. The light should only just flash on momentarily.

4. Is the rear fuel filter installed with the correct orientation? I.E. flow direction.

5. Are the connections at the fuel supply pump clean, tight, and show a good steady 12 volts? Is the connection for the supply pump ground wire clean and tight on the bodywork? There's another spade connector in the trunk on the hot wire to the fuel supply pump. Check it clean and tight also. Check the connections clean and tight for the fusebox for the supply pump. It's the small one with two fuses in it (one for the pump and the other is a spare). It's located right beside the main fuse box on the drivers side under-dash.

6. Can you make the pressure light come on just by reving the engine? If you can, (lawyers please stop reading at this point) try momentarily pinching the fuel line downstream of the injection pump OUTLET. The theory behind this is to create more pressure by even further restricting the recirculated flow. If the light goes out when you do that, then the pump is probably weak.

If all this simple stuff looks good, about the only thing I can think of is to hook up your tester to a "T" fitting, run the hose out the hood, prop it under the windshield wiper, then go test drive, noting what the fuel pressure does.

I'm still betting on a weak pump.

Last summer I had my Alfa on a long (1000 mile) trip. Towards the last few hours, the light started coming on after a long run, first intermittently at high rpm and throttle load, then started coming on more and more frequently and sooner. I even stopped and disconnected the rear fuel filter thinking it was clogged, but that didn't help. It seemed to do better after stopping for gas for a while (pump probably cooled down a bit). But finally after a couple of hours, the light would come one steady after a few miles and then finally the engine started stumbling from fuel starvation.

I went through a lot of the machinations you are right now.
Finally changed the pump and VOILA . . . . light went out and stayed out.

It shouldn't hurt the injection pump to run with just a slightly intermittent pressure light, but be assured that if it's a bad pump, it's going to get worse (and maybe quickly) and might strand you someplace.

Keep me informed. If you'd like to talk on the phone send me a PM.
 

·
Premium Member
Joined
·
1,456 Posts
Great post you guy's, I've been following the thread just in case this happen's to me. Roadtrip, you provide great info.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #8
it may hve been a leaking main fuel filter.
Please tell me the seal (ruber round gasket) goes arround the top of the filter cup or under the top of the filter?
Thanks,
Steve.
 

·
Registered
Joined
·
9,977 Posts
The front (main) filter seal (a rather thin ring seal) goes in a channel in the top part of the filter body (the part that bolts onto the frame of the car). It should be obvious by the diameter of the seal. Then, the bottom can is bolted through the center and pulled up into the channel and against the rubber seal. The filter itself has a small rubber seal and a spring, if I remember correctly.

Be sure that the front fuel filter is clean and free of varnish. I've found that it's easier sometimes to just remove the whole thing to clean and refit the filter and bottom can. That way you can make sure that the can edges are centered in the top channel and the seal isn't distorted. It's a lousy design . . . . what can I say? Most of Alfa's stuff is engineered brilliantly . . . . but some of it seems like it was designed on a napkin on Saturday afternoon after way too much vino and using the British "Hardest Way" Rule of Engineering.

Be sure to lubricate the copper washer on the center bolt before you tighten it. If you do remove the entire filter assembly, be careful not to break the bakelite fuel low pressure switch . . it's rather fragile.

It'd have to be a lot more than just some seepage from a misaligned seal to cause enough pressure loss to bring the light on . . . . I'm thinkin'. I hope that's it, however.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #10
Well RT you are right the leaking filter seal was not the problem.
I noticed that the light would flicker on as I raised the RPM's under no load at about ~3100 then go off and come on steady at ~4300 so I removed the sensor cable on the main filter and cleaned the contacts with fine sand paper. Now the light does not come on under no load but does when I am driving at the same ~3200 RPM's or so and seems to want to go off as RPM,s build but eventualy stays on steady at ~4000 RPM.
I think I will replace the sensor and see if that corrects the problem.
p.s. Autobooks owner workshop manual lists the following as propable causes:
1- faulty fuel pump(you said the same)
2- pressure switch faulty
3- fuel line or filter blockage(you said the same)
4- pressure reliefe valve stuck open(how do I check that?)
Thanks,
Steve
 

·
Registered
Joined
·
9,977 Posts
Hmmm. . . . . could be a bad pressure switch. It almost sounds like it's maybe sensitive to vibration frequencies (intermittently bad pressure switch?). Did you make sure that the connection is nice and tight after you cleaned the terminal?

Pressure switches are kind of expensive (about $30), so I think I'd do a "T" fitting pressure check first, before I spent the money on something you don't need. As far as a pressure relief valve goes, there's one in the supply pumps that have 3 outlets. Yours (a '74) should have only two.

I didn't think there was another, unless it's in the top portion of the front fuel filter. I'm out of town right now and don't have my schematic in front of me. I suppose you can remove the top section of the front filter (2 nuts) and clean it with carb cleaner.

I think you're down to doing a T fitting pressure check. That would tell you for sure what's going on.
 

·
Registered
Joined
·
989 Posts
Great info from RT. I had a 78 spider, that had
a second pump in the fuel tank, this went bad
and caused the low pressure light to come on.
Im not sure if these pumps are on the 74's.
I also had the gas tank vent/evaporation system
plug up, and the tank would build up negative
pressure as the tank got lower. It finally got so
bad that I started popping fuel pump fuses.
I think it was to hard for the pump to suck gas out.

Just two more things worth checking out before
forking out $300 for a new fuel pump.

Good luck.
 

·
Registered
Joined
·
9,977 Posts
I was assuming that you'd have noticed a plugged fuel tank vent line. Keven is absolutely right . . . . a plugged tank vent will definately really screw up the entire system resulting in perhaps a burned pump or a collapsed fuel tank . . . both really undesirable from a pocketbook standpoint.

Your 74 doesn't have a in-tank boost pump, or at least shouldn't if the car is original.

A replacement supply pump is about $160 from Centerline, or about $50 for a used one on Ebay.

If you decide to R&R the pressure switch, be VERY careful. The bakelite tower on the switch is VERY easy to break.
 

·
Registered
Joined
·
989 Posts
To check if you have a plugged vent line, run
the car for a good while, then shut down and
remove the gas cap. If you get a whoosh of air
entering the tank, you have a plugged vent line.

Hope this helps.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #15
Thanks RT and Keven,
I will try to run the pressure test tomorow and I will check the vent thing tonight.
Will let you know.
Thanks,
Steve.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #16
Thanks RT and Keven,
I will try to run the pressure test tomorow and I will check the vent thing tonight.
Will let you know.
Thanks,
Steve.
 

·
Premium Member
Joined
·
16,232 Posts
FWIW, and assuming (cause I don't know for sure) the 2000 and 1750 main fuel filter assys. are the same, the 1750 shop manual shows the pressure relief valve, set at 16-18 psi, on/in the main filter assy. on the return side (the hoses closer to the body). You need BOTH pump pressure and volume readings, since one is possible without the other, to accurately diagnose an ailing fuel pump. Of all the Spica Alfas I've worked on, not a one ever needed a pressure switch or had a relief valve stuck open. Always a first time though. I'm with Roadtrip on this one; the pumps toast.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #18
Hi all:
I fitted a cheap pressure gauge between the fuel filter and the SPICA and I am getting ~8-10 PSI (mostly 8) with the engine off, if I switch the engine on the gauge needle vibrates to much to get an accurate reading but it seems pressure goes down to~8 PSI when I hit the trottle and up~18 PSI as it revs down but I think it's about~10 PSI at idle.
Is this pressure too low?
Thanks,
Steve.
 

·
Premium Member
Joined
·
16,232 Posts
Gave a little thought to on how to test the pressure relief valve (and fuel pump pressure) and came up with this. Refering to the crude diagram, insert a pressure gauge (30psi min) at #1 and note the reading with KEY on~engine 0ff. Im thinking it should be 16 to 18 psi., but cant find a factory spec. Does anybody know?¿ Next, take a reading at #2. They should be about the same if there's no restriction in the filter assy. Assuming a good fuel pump, this next test will tell you what the pressure relief is set at, or if its stuck closed. Slowly squeeze the fuel line at #3 while watching the pressure gauge. If the gauge starts to go over 20 psi, STOP. The pump is OK and the pressure relief valve is stuck closed.
0r whatever the gauge tops out at (1750 spec is 16-18) is what the relief valve is set at.
Next slowly squeeze the hose at #4. If the pressure wont reach 20 psi, the pump is no good, assuming, of course, everything on Roadtrips list was already checked. If the pressure does reach 20, the pump is OK and the valve is stuck open.
Don't have a Spica car handy to test this procedure (or modify it!)so you're the Guinea pig:D .
Good luck!!
 

Attachments

·
Registered
Joined
·
9,977 Posts
Hmmmmm (again) . . . . . . . When I get back home I'll check the exact system pressure in my Alfa's and let you know what it is under various conditions. Since I've never had to do it, I'm curious to see what it is. I'm thinking it ought to be better than 8 psi, but then again, according to Wes Ingram, anything that extinguishes the low pressure light is good enough. I don't know anywhere that such a detailed troubleshooting procedure is written down, but maybe we could use this tech problem to start the first one on alfabb.com.

If all else fails, I have a spare supply pump and front fuel filter assembly that you can borrow to R&R and narrow it down. Like women, Alfa's won't always tell you what's wrong right away. They like to make YOU suffer for a while as well.
 
1 - 20 of 24 Posts
Top