400i Starting Problem

Cannot give you definitive answers here as this is a problem I did not have so far on my car. On my cousin 412 (that has different pumps), there was a leak in a hose, the car was lacking power at full throttle and would not start when hot.

The fuel pumps do not work the same way when the car is cold or hot. The idea is that when the car is hot, accumulator are supposed to provide the required gas pressure (not the fuel pumps). If you've got a leak somewhere, the pressure in the accumulator will not be sufficient so as to feed the injectors.

There are two relays for the pump, plus a master relay that can deactivate the other two. When the car is cold this relay just lets the pump work, but when the car is hot it will shut off the pump until some airflow is sensed on the K-jet. You should just have a look at the wiring diagram that highlights the 3 relays, the airflow sensor, thermo-switch, cold valve switch and start valve timer. All these are involved during a hot-start...

I let others further describe this, but the first place I would be looking for is a leak. For testing purposes there are some possibilities to bypass the hot/cold control (see comments in this forum on how to disconnect the airflow sensor, that's the green plug on the k-jet)

As a side note: if the battery is weak, do not jump-start the car as the dinoplex will be fried.

 

If it is not holding residual pressure they can vapor lock easily especially with reformulated gas. If the battery is strong enough giving it full throttle and cranking a while should start it. Your starts with starting fluid strongly suggest this is the issue.

 

There is also a cold start injector on each bank that gets power for cold cranking & pulsed power for hot starting. I had problems with mine previously not getting the pulsed power when hot starting & it had the same symptoms you describe. There is a relay that supplies the pulsed power (similar to a blinker can but pulses twice as quick) in the relay block. My relay had a dry solder joint on an electrolytic capacitor causing it to fail. I replaced the capacitor & reflowed the solder joints & all good again.

Cheers,
Al

Image Unavailable, Please Login

 

If its a hot re-start problem (only sat 30 minutes) its losing rest pressure. There are a number of things that will cause it to lose its rest pressure which I wont bother listing. Shooting it with ether to get it to run is a very good indication thats your problem.

And I now see Brian wrote pretty much the same thing! Next time Ill read the entire thread.

 

Internal back to the tanks

 

Agreed, I had this situation of no start on a hot engine, in this particular case it was eventually traced down to a leak in the pressure accumulator. In summary if the start was a minute or so after shut down, no problems (residual pressure was still good enough), if the start was 10 minutes after shut down (for example a refill at the gas station), no start at all, the only way was to wait long enough for the engine to be sufficiently cold for the cold injector to work and start the engine. Like Paul said all scenarios of pressure losses (fast or slow) are possible.

 

If you're stuck in a situation like that unplug the fuel pump switch on the sensor plate housing and push the sensor plate down with your hand, key on. It'll prime the system, you'll hear the pumps come on. Then attempt to start the car.

 

Don't think you need to do both actions, Paul - either:

1. Unplug the safety switch on the sensor plate housing + key "on" = fuel pumps run

or

2. Key "on" + push the sensor plate down on the sensor plate housing that has the safety switch = fuel pumps run

I prefer #1 as it can be done fully-dressed with no tools and little risk of getting dirty

 

When I had hot start problems did a few things which solved the problem.

- replaced fuel pumps
- tested fuel injectors. Leaking. Replaced with new.
- fuel distributors leaking at o-rings. Rebuilt fuel distributors.

Then had a bit of a cold start issue, which was solved by rebuilding the warm-up regulators.

 

Or into the cylinders.

 

Thanks Paul, that sounds much better than waiting for one hour at the gas station!

 

The fact that you can crank & crank with no fire at all indicates to me that the start-up injectors are not getting fuel or power.

All these other issues can be a cause of poor starting but if the start-up injectors are functioning you should be getting the odd kick of life. The fact that a squirt of starter fluid & it starts & runs fine says the fuel pressure must be there so I would look at the electrical side of the start-up injectors.

The K-Jetronic is a mechanical fuel injection which relies on airflow through the conveyors to move a plate which moves the metering piston in the fuel distributors to control the flow to the injectors. The original starter motors crank the engine at a very low speed so start-up injectors are required to give an initial charge of fuel to get the engine to kick over & bring the mechanical fuel injection into play.

 

Not correct. If the engine is warm the COLD START injectors are off line and they only inject during cranking using the starter solenoid as the trigger. Using ether does the same thing the cold start injector would do, fills in the gap until the mechanical system can take over. A cold start the next day would have no rest pressure or very little so the cold start injectors are needed even if its mild out.

 

Not when hot. There is sufficient displacement of the plate at cranking speed when the engine is hot to start the car. There is a reason Bosch referred to the start injectors as "Cold Start Injectors".

 

Sorry if I have mislead or upset anyone but I have experienced the exact same symptoms as the original post & in my case it was relay 1 that rectified the problems. I just thought I would offer this advice as it is a quick & easy thing to check before going through the more expensive & time consuming process of fitting new accumulators etcetera that I went through before fixing this fault.

Image Unavailable, Please Login Image Unavailable, Please Login

 

Your relay box looks like a generation 1, not the failiure prone one that can be found in the gen2 / 412.

My car was a late gen1 400i (january 1982) with double alternators, but I do not have this additiobal relay, which year is yours?

 

Thanks for this info it is very interesting.

I have two 1980 cars & both have relay 1.
I also have a 1982 one which is apart for restoration. I just checked this one & it does not have a relay one. It appears that Ferrari made a change between these years to increase the duty cycle for the start-up injectors whilst warm cranking from around 50% to 100% duty cycle to make warm starting easier. I might retrofit this upgrade to the earlier cars sometime.

 

The problem is probably insufficient fuel pressure to crack open the Bosch injectors. The K Jetronic system needs a high enough fuel pressure to work. The cause of low fuel pressure will most likely be electrical, ie not enough current to the fuel pumps, caused by a problem in the fuse box. Low current will allow the pumps to run, but not produce enough pressure to crack open the injectors.

The fuel system in these cars is essentially duplicate, so if you had 1 dead fuel pump, or clogged filter, etc, the other side of the engine would still attempt to start and run, (they will run as a 6 cylinder ).

Also you have enough spark to run the engine ( runs with starting fluid )
And your plugs are dry ( symptom of not enough pressure to crack the injectors ) , assuming there is petrol in the tank

You can take move the high current fuel pump circuits off the fuse box and use the original circuits just to switch some new seperate high current relays you install for the fuel pumps to ensure enough amps reach the fuel pumps.

M

 

To be honest I wouldn't do that on a generation 1, as the relay-box is much better than on the newer models. The relays are directly bolted on the harness and are not passing through the cheap PCB that can be seen on later (gen2 & 412). That's even more obvious for the fuel-pump relays: see on Al Campbell diagam, it is super easy to crimp new relay terminals on relay 1,2,3,4,5 (as a last resort).

Also on generation 1, if you bypass the stock harness, you bypass the ammeter readings, and as the pumps are what draw the most, the ammeter becomes useless.

As per Al Campbell suggestion one can also use the very silver grease he suggested a few months back (Thanks for the tip by the way ), this will cure most high amperage related issues on a generation 1 car.

 

I have this exact same problem Jeff - So far I have replaced my coil and my distributor cap, but I have not been driving my car regularly. I'm going to be following this post in earnest. I have a feeling this issue will rear its ugly head again.

Also Jeff I'm very curious about your oil leak - I'm going to send you a PM!!

Jim

 

Jeff asked, "One question, is California fuel more prone to vapor lock than the rest of the states? "

CA has tight limits on maximum vapor pressure of fuels and therefore should be less prone to vapor lock, unless you are in the middle of a wild fire.
Ken

 

curious if there was a resolution to this issue. My 82 400i is doing the same thing. Been off the road for 20 years, new pumps, etc but i didn't replace the accumulators yet. Thinking that's my next move.