Fuel Injectors (again)

The After sure looks great. What’s the name of the shop where you took it to?

 

I did that.

 

That's because once it's running all that matters is that they are open since it's CSI. Doesn't matter what pressure they open, or if they leak.

Be interesting to see it it solves your warm start problem.

 

Leaking is a real problem when you turn it off. Thats were the warm start problem came from. Residual pressure goes away and the fuel in the lines vaporizes. Since fuel injection is a hydraulic system like brakes it now has air in the lines and has difficulty making enough pressure to open the injectors. Takes a lot of cranking to make that happen.

 

It's too bad that they didn't check flow rates pre/post service. As mentioned earlier in this thread, the differing injector opening pressures will cause different flow rates which is not ideal. I have confirmed this on my test bench and it has been documented here in the past as well: Flow Testing Results of OEM CIS Injectors | FerrariChat

One thing that I'm perplexed by is the significant change in opening pressures that was documented pre/post injector service. In my experience cleaning/servicing injectors can definitely correct leaky injectors and poor spray pattern but I have never seen this dramatic of a change in opening pressures pre/post service. The opening pressure of a CIS injector is determined by the internal spring which exerts a force on the pintle keeping it closed until fuel pressure overcomes the spring pressure. The internal spring is fixed and can not be adjusted so I'm having a hard time understanding these wide swings in opening pressures pre/post servicing. The increase in opening pressure after correction of leaks makes some sense but I've never seen a 35 psi/2.4 bar increase as was the case with injector #8. I'm especially scratching my head over injector #1 which did not have any leaks pre service and saw a 9 psi/0.6 bar increase in opening pressure.

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Finally, I'm glad to see that there is agreement that leaky injectors can cause hot start problems on CIS cars. While in my experience a failed fuel accumulator seems to be the most common cause, I have seen leaky injectors be the culprit on several CIS cars that I have worked on noting that there has been debate on Fchat before regarding this. See post #14-20: 308 QV hot starting problem, new | FerrariChat

 

One additional thing that I would add for the originator of this thread or anyone else that is planning on replacing/servicing their CIS injectors. From time to time I will work on a set of injectors or put together a perfectly balanced set of injectors (equal opening pressures) and after they get installed the car runs a bit worse. It's almost always the case in this situation that an AFR adjustment is needed. It is usually on cars that have their original fuel injectors in place and have had mixture screw adjustments performed over the years attempting to compensate for progressively abnormal performance of the fuel system components. The same is true for a rebuilt fuel distributor after the flows are dialed in evenly. Especially on those with significant flow variances pre rebuild. Hope this helps!