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CIS system management of boost

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I may be buying an Esprit next year, so I'm in learning mode.

Just out of learning curiosity - Was wondering how does the CIS system on the HCi (and 88s as well, I suppose biggrin.gif ) handle boost as far as spark and fueling go?

Obviously EFI systems programmatically adjust the parameters as needed under boost; but how does it work on an engine with K-Jet and a mechanical distributor?

Also, what is the part that I'm pointing to with an arrow in this picture?




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Haha, I thought you already received a reply to the "arrow" question on Lotus Talk!  And I was right hehe...


I'm sure that particular question, and the same photograph, was simply an oversight on your part :mellow: . As for the rest, greater minds than mine will surely respond here, as they did on Lotus Talk...


Anyway, if you want to learn masses about Bosch CIS, you might also have a go at the VW Vortex and see what some of their members have done--adding turbos, shims to the fuel distributors, and intercoolers to normally aspirated VW's, (all of which were never meant to be boosted)...and managing to arrive at, frankly, quite astonishing gains in overall performance (and equally astonishing engine meltdowns on occasion).





1986 Esprit HCI (Bosch-injected)

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Welcome to TLF Mike. :welcome:


Duck over to the Introductions section and say hi in there as well. :)

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

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Your question: Obviously EFI systems programmatically adjust the parameters as needed under boost; but how does it work on an engine with K-Jet and a mechanical distributor?

K-Jetro system is very rudimentary and does not have all nice features of the later CIS systems. 

It has the O2  sensor and a computer box, which is nothing else, but a lambda processor controlling the FV (frequency valve); no other sensors are connected to the box.

Every CIS has two separate hydraulic circuits, Control Pressure system, which acts as an information bus, and System Pressure circuit, which is actually delivering fuel to the cylinders.


On the basis of the O2  sensor reading the computer sends a signal to FV telling it how much fuel to bleed out of the Control Pressure circuit (return to the fuel tank), controlling that way the CP pressure to achieve Lambda=1 mixture.

In closed loop mode, CP pressure signal manipulates the System Pressure via the FRP (fuel pressure regulator, also called WUR-warm up regulator), which differentiates the amount of fuel sprayed in by injectors.

In CIS system, since mechanical injectors are just spraying nozzles, the amount of fuel delivered is proportionate to the System Pressure. 


On boost, at WOT, the system goes into an open loop mode (no Lambda input) and  computer pin No. 7 is grounded delivering  the boost enrichment signal to WUR,(65% FV duty cycle meter). This extra fuel can help prevent detonation when running higher boost levels. WUR pre-set amount of fuel. On our cars, that amount stays constant throughout the rpm range.


Let's assume that we replace the stock turbocharger with a modified ported super 0.60 A/R unit, which will increase the air flow from 380CFM @ WOT to 440-450CFM. The problem is how to enrich the mixture to bring AFR to the acceptable level at WOT at hi rpm range (5500-7000rpm).  

Me thinking:

The pin 7 is grounded by fuel enrichment module above 3250rpm. Above that rpm value the system goes into an Open Loop mode and FV duty cycle goes up to a steady to 65%. How fuel can be added throughout 3250-7250rpm band? Since FV duty cycle is Constant 65%, obviously, the engine will lean out at the top rpm range.

It would be nice if we can bring AFR to the safe level without overfueling at the lower rpms. Above 3250 rpm, we loose the Lambda tracking since the CPU is NOT in closed loop.

 Pin # 7 signal is an ON-OF trigger only and FV duty cycle is pre-set by ECU’ electronic guts and WUR’s WCP. If engine air flow volume is modified, the Warm Control Pressure has to be tweaked (one time adjustment) at the WUR, per instructions below


At 10 psi & 3250 rpm engine flows 196 CFM,  840 lb/h of air and requires  67 lb/hr of fuel @ const AFR 12.5:1

At 10 psi & 7250 rpm engine flows 436 CFM, 1860 lb/h of air and requires149 lb/hr of fuel @ const AFR 12.5:1


In 3250rpm to 7250rpm band the fuel system can only deliver a constant amount of fuel, (open loop, pin #7 grounded, FV DC=65%=CONST).

If we choose 5250rpm as a median point and adjust WUR to deliver 105lb/hr  fuel @12.5:1 AFR, (constant delivery), since air mass flow is variable, we will end up with 7.7:1 AFR @ 3250 and 17.25:1 AFR @ 7250rpm. Not acceptable!


We have to start with at least 10:1 AFR @3250 (81lb/h of fuel) and keep delivery constant, up to 5000 rpm (15.4 AFR). At this point an additional enrichment is a must!


 Mod # # #:

To provide gradual Warm CP adjustment above 3250 rpm, the simple solution may be a vacuum/ boost sensing mechanical WUR, as on Audi 5000TQ or Volvo 240T, OR  a digitally controlled UT-WUR w/microprocessor.


To cover fueling demand at the top of rpm band under the full boost, an additional fuel has to come “on top” of the pin #7 enrichment and Mod # # # delivery, which has to be proven empirically. To properly execute this, one may install an adjustable Hobbs Switch in parallel with "mystery" Bosch capsule. Such switch would short the pin #11 @ the top of the boost range/rpm, perhaps at 8 psig (assuming 10 psig max boost).

 Another solution could be a Split Second AIC-1 or controller and 2 or 4 auxiliary electromagnetic injectors delivering additional 64lb/h upstream (same concept as Esprit SE).



Another, perhaps simpler solution would be to replace stock mechanical WUR with boost sensing unit of the Audi 5000 or Volvo 240T.

Perhaps much better would be installation of Unwired Tools Inc. Digitally controlled WUR, UTCIS-PT

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