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fuel cut

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I am working on a friends 1986 esprit turbo, it is a usa car so has the bocsh k-jetronic fuel injection on it.

it is getting fuel cut when boost gets to 7psi while driving, so I thought the wastgate is stuck and is overboosting. 

but the owner (unknown to me) bypassed his over boost switch. ( he unplugged the wire harness from it and stuck a wire from one pin to the other in the harness)

also when I drive and slowly build boost i found it will start to cut just alittle at 5.5 psi and then a little more at 6 psi

so is there any other system that will cut fuel due to boost?  or any other thoughts

it drives good when at low boost levels

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Hi Brian,

When you cut, is it as in completely cut, shutting down or missing?

Did you notice if you can get to higher speeds without using too much boost?

I'm wondering if it is really boost related or just starving...



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The rev limiter cuts fuel at 7000 an on-off switch. :o


The Engine Overspeed Module cuts fuel to the pumps under those circumstances. It is located under the carpeted panel near the RH rear window on a G-car. Inspect the connections to it for burning, they carry a high current.


Usually, if the boost control is bypassed the engine will cut out if the boost goes over 1.0 BAR.  If that is what's happening FIX IT...the engines won't take that much boost for long before they explode!





If the engine is just 'starving' for fuel, check for ANY vacuum or intake leak, and for free movement of the air metering mechanism under the air filter housing. If all that is good, then it might be time to look at the WUR (Warm Up Regulator, that regulates fuel supply both warm & cold).

There is a very good explanation of the Bosch K-Jet FI system workings in Section LE of the Service Notes, along with troubleshooting procedures.




Edited by CarBuff

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the cut has nothing to do with the rpm ( I will check the over speed module but I do not think  that will be the problem, but hey you never know)

its runs perfect under 5.5 psi of boost any more and it starts to cut it out. just a slight cut from 5.5 to 6.5 and full cut at 7psi ( it is a cut, not just running out of fuel)

I rebuilt the worm up regulator last year ( fixed that problem)

I was wandering what actually cuts the fuel?  in other words the over boost switch sends a signal to something (like the ecu or a relay) then that sends a signal to the component that actually cuts out the fuel

this way I can go thru the system one component at a time till I find the problem.

rather than making them spend money on something that may be working just fine

I bought some books on bosch fuel inj one of them is really good, but they say nothing for boost related setups

I will look at the service notes again, maybe I overlooked something

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There is an overboost circuit that cuts fuel if the boost exceeds 1.0 bar.  Or, if the system ***thinks*** the boost is too high.<_<



Have you inspected the wastegate, specifically the diaphragm and the shank of the poppet valve? The diafragms will have a thin slit if worn.  The poppet valves can wear at the boss inside.


Another thing I've seen is that one of the two fuel pumps is failing so you cannot get full pressure under high demand. Have you connected a fuel pressure meter as outlined in the Service Notes?


The Lotus Service Notes explain the Bosch system rather thoroughly (as the factory knew that the dealer techs would not have a lot of experience with the system).



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ok, so here is an up date

I ordered the parts to rebuild the waste gate

also I found on the very last page of the lotus service notes it tells how the over boost and over speed module cut out fuel.

the over boost switch tells the r.p.m relay to cut power to the pumps and the over speed module tells the 2 fuel pump relays to cut ground

it also has a roll over switch that cuts power to the pumps if you ever flip your car.

so to by pass all these systems;

I gave the pumps a direct ground - did not change anything

jumped the rollover switch - did not change anything

gave the fuel pumps a power supply straight from the battery to the fuel pumps - this fixed the problem, now we know the system at fault

so I had another r.p.m relay that I know is good and switched them out - did not fix it

so I jumped the to yellow wires ( fuel pump wires) from the rpm relay - did not fix anything

so I am confused, the over boost switch is bypassed and the rpm relay is bypassed, yet it still cuts fuel. how is that possible


I ordered the parts to rebuild the wastgate they should be here in a week or so

maybe I will get lucky but something tells me there is more to it then that


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It's not unheard of for problems to exist with the wiring and connectors.  They carry a good deal of current for their size.


You need to look carefully at the plugs connecting the EOM (Engine Overspeed Module), which is located under the carpet by the RH quarter window.  From memory, the white/green can look burned and this will cause issues.


Also, check the sockets of the two fuel pump relays. The current draw can heat them up, cause loose connections, and you may be losing one of the two pumps.


Also, be POSITIVE that the fuel pump wires at the + side of the battery are tight.


If you know another HCPI 86 or 87 nearby, swap the EOM.  These are expensive and rare, but JAE Parts in the USA might have them. (Ask about a return policy).  If you can't find anything local, PM me and I'll see if anyone has one that you could 'test'. Note that the EOM for the 86-87 arte not the same as the Bosch EOM on '88s.

My phone # is in the Masthead of the Lotus Ltd magazine, as "Esprit Tech Coordinator"... :ermm:

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