81 308GTBi Fuel pump fuse keeps burning up unless...

Hi guys,

I have a weird situation. 1981 308 GTBi keeps burning up the fuel pump fuse, UNLESS the cold start injector is disconnected. What would cause this?

I'd greatly appreciate any assistance on this

LG

 

Witchcraft?

Seriously, there is no relationship at all between those two systems UNLESS someone has made some "modifications". Does your fuel pump run with just the key "on" and the engine not running (it shouldn't)? If it does (and your safety switch is plugged in) you should have a look to see if the wiring of your ...101 start injector relay and your ..113 fuel pump relay matches, or does not match, the wiring shown on your 195/80 (euro) OM or 216/81 (US) OM. The other thing to do would be to measure the current in the fuel pump fuse #3 both with, and without, the CSI plugged in (it should be something like 9-11A unless you've already had the fuel pump "updated" to the wimpier lower-current substitute).

Question -- Does the fuel pump fuse blow immediately (or within a few seconds) if the CSI is plugged in, or does the engine run for a few minutes and then the fuel pump fuse blows?

PS Also, wouldn't hurt to have a look at the fuseblock in the area of fuel pump fuse #3 just to see if anything has been modified/added/molested. There should only be a single wire connected to the bottom of fuel pump fuse #3.

 

LOL, Not sure Steve. But it could be some demonic stirring

But seriously, it does take a few days to blow with the cold start injector connected. Without it, no problem. I did happen to notice that someone had a toggle switch connected to the coolant tank sensor and my assumption is that this may be for fuel enrichment but I am not really sure.

Other than that, I have no clue.

 

So, we have put in a replacement fuel pump #113976, to see if that helps. I did use my temp gun and noted 157 degrees F measured at the fuse. That is pretty high, if you ask me. But I do not have ANY clue what would be causing that.

 

10A (the approximate "normal" CIS fuel pump current) flowing thru what you would think was a rather decent electrical connection can cause that (the heating at the connections, I^2*R, can be quite large even at low R because the I is so high). Do you still have the stock fuse block, or have you upgraded to something better? If you still have the stock fuse block, you should at least solder the rivets to the metal plates of the fuse block on both sides and at both ends of the fuel pump fuse IMO.

PS If the problem is heating at the fuse block connections = a new fuel pump (if the stock 60mm diameter) might make the situation worse as those tend to be "tight" and draw even more current when new. If your "113976 replacement" is the smaller 52mm pump (with the zig-zag plastic piece on the OD for mounting) = that could help things as that pump draws less current (but can run out of flow at high RPM -- most times that pump is OK, but there are some pumps in that population that meet the manufacturer's flow spec but are below the F flow spec).

 

Hi Steve,
Yes, the fuse block is still the original one. I'd like to think the wiring in the vehicle, for the most part, is decent. The only thing I've seen that wasn't original was the radio wiring, so in that aspect I am hopeful. The wiring in the engine compartment wasn't compromised as far as I could tell either. As for the fuel pump, no, it is the original diameter not the smaller one. I am truly hoping that this particular issue is not in conjunction with the hot restart issue, I.E. that i have to have someone in the vehicle turn the key to run while I press the flap valve down on the CIS (I can then hear fuel pressure increase in the system) and then I can get it fired up again.

 

You are new here -- the injected 308s burning up the fuel pump fuse holder in the stock fuse block is not at all uncommon, and basically spawned an industry of people making whole replacement 308 fuse blocks (Birdman, TurtleFarmer, etc.).

 

Steve,
I seriously thank you for all the help you've supplied me in the past and as of late. If there is any way I can repay this, please, let me know.
I have seen the larger fuse blocks and relay boards, I didn't know these had been at issue as well. I am forever learning more and more in the wonderful world of Ferrari repair

 

Also, another question, fuel system related:

I have noted a weird start issue after it has ran. I guess after some sort of heat soak, I have had to tap on the CIS flap to get fuel moving, as if it is a little stuck? I have tried it with the cold start injector disconnected as well as connected too. I don't know if these diaphrams are issues. I DO know that the adjuster for the flap has never been touched as there is a metal plug in place at the top of the tower.
I know I am throwing a lot of stuff out there, but it seems to be all related. I just really want to get this right so that I can have a happy consumer.

 

Warm restart difficulty on the CIS models is most often because the regulated fuel pressure is falling too quickly after warm engine shutoff. It should stay up at about 3 bar for 20 minutes so I'd suggest that you measure the fuel pressure after warm engine shutoff as the first step to investigate. If that is the reason for the trouble, it can have many causes -- bad Accumulator, bad fuel pump check valve, bad o-rings in the pressure regulator section of the fuel distributor, or even someone using the wrong CIS fuel pump and leaving the fuel pump check valve out completely. If you can post a picture of your present fuel pump assembly, we'll easily be able to tell if that last cause is the issue (and we've had that happen many times here).

Can't recall anyone ever reporting that as an issue. The test there would be (with key "off") to crack the fuel line connection to the cold start injector open to ensure that there is no fuel pressure at all (wrap a rag around the connection while loosening to catch any fuel spraying out of there is some pressure). Then just use a finger to deflect the airflow flap and ensure that it moves smoothly, easily, and returns to the home position well. Do you have a copy of the 281/83 Mondial8/QV WSM? Section D covers your K-Jet without Lambda CIS system.

If you did have something physically messed up in the airflow flap + plunger mechanical mechanism, I'd think it likely that you'd have other runability problems other than just a warm restart issue.

 

Hey, we were all new here at one time. One of my favorite Ferrari-related quotes is this: "There are only two kinds of Ferrari OEM 308 fuseboxes: those that have left you stranded and those that will." - Birdman
More than just future-proofing you and the car from future electrical glitches, you'd be amazed at what one of the new fuse panels can do for you: faster windows, brighter lights, more powerful fans, better looking children, the list goes on and on. Srsly, one of the best, least expensive investments you can make in your car IMO.
- Dave

 

To the OP:

Do yourself a huge favor. Do a search on the "redesigned fuse panel" thread by TurtleFarmer in this forum and read it.

The pictures and text in this above noted thread will show you why this is a Must Do for you.

DM

 

Image Unavailable, Please Login

 

Well, I must say, FIrst.... WOW, that's a pretty modern style fuse box design. Definitely will inform the customer of it.

Secondly, to Steve, The fuel pressure requlator and fuel filter are new. OEM parts. The fuel pump is also new, 113976 with internal check valve. The wierdest part of it all , is that is starts right up in the morning.

SO, I am totally stumped. Also, NO, I do NOT have a copy 281/83 Mondial8/QV WSM. If you could point me in the direction of one, that would be great. I do have Dropbox.

 

That's not weird at all for a car with the residual fuel pressure falling too quickly at warm engine shut off. In the morning, things have cooled off enough for any fuel in the system that has vaporized to turn back into liquid. Also, during a cold restart, the fuel squirt from the cold start injector aids starting.

"New" does not always mean "good". IMO, you should still MEASURE the fuel pressure at warm engine shut off to see if it is falling to quickly, or not. Also, you should see if any liquid fuel is wrongly exiting the vent nipple on the Accumulator when the fuel pump is running -- on the US version, they added a hose to the vent nipple that goes back to the tank so this hose has to be removed to see the problem (whereas on a euro version, the Accumulator vent nipple is left open to atmosphere so a leaking bad Accumulator is obvious).

PS Your statement that the "fuel pressure regulator" is new seems odd. The fuel pressure regulator is part of the K-Jet fuel distributor. If you mean that you replaced the Warm-Up Regulator (aka Control Pressure Regulator) = that's good, but has nothing to do with the o-rings in the fuel pressure regulator section of the fuel distributor that can cause the fuel pressure to fall too quickly at warm engine shutoff if they fail.

This link will get you a pdf copy of 281/83:

https://www.dropbox.com/scl/fi/twng41f9fpi3ipww7q95v/Mondial8qv_workshop_281-83.pdf?rlkey=5sgpj4yz33jepzrec4x8lcwel&st=a4apcg7s&dl=0

PPS Send my portion of your fee to my Paypal account .