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Chris89turbo

1990 SE - Stalling on acceleration

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Hello everyone, I have been working on a running problem with a 1990SE for about a month now, and I am approaching the point that I have run out of potential components that are faulty, so I want to see if anyone has some other ideas I might try. I am about fresh out of ideas myself.

Here is the issue: When I bought the car, I could tell it was not running right. I had an 89 Turbo the previous year that ran like a sewing machine. But this one doesn

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50 psi seems a bit much -- I'd lean towards a fuel pressure regulator as the possible culprit.


Visit Sanj's Lotus Esprit Turbo SE pages

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sanj, according to the manual, "The system operates at anacceptable pressure range of 30.5psi - 55psi depending on engine conditions while running"

We are idling at 50psi... Well within range.. Are you thinking that is still too high within the acceptable limit?

Chris

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Do you have an exhaust back pressure valve still fitted? If so, check to see if it's not seized closed. Otherwise check the O2 sensor.

How does it stall? Suddenly with a pop or just die? Is it overboosting?

David Walters

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Normal Ignition ON pump pressure should be about 40-47 PSI.

Use the fault finder CHART EMH4.7 (Lotus service notes) to inspect your fuel system.

You can download these notes from this website.

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Have you run Freescan on the car?


88 Esprit NA, 89 Esprit Turbo SE, Evora, Evora S, Evora IPS, Evora S IPS, Evora S IPS SR, Evora 400, Elise S1, Elise S1 111s, Evora GT410 Sport

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Oooh yar - Freescan. Also, you say timing is good. Does that include valve timing?


British Ambassador to Florida, New York, Denmark and Newfoundland.  And Sweden.

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I read through all this thinking fuel pressure, but right at the end, Spark break down, don't know how you test it on an SE, but it could be breaking down under load.

Roger


Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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check the o2 sensor, my s4 had massive overfueling would run great then be awful and used much fuel, may be a bugger to out. if i remember rightly the symptoms pointed to the ecu but it was the o2 sensor


It's Oogies turn to boogie

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If you save your frescan results and post them up here I'm sure someone with a more in depth knowledge would take a look for you and let you know if anything is amiss.

Good luck with the O2 sensor, hope it does the trick!


Chunky Lover

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Hi Chris,

Once you've checked those bits and report back to us then we'll have another go. If it did have to pass California emissions then it's likely to have one of these EBVP fitted I think. This basically blocked up the exhaust during warm up cycle then opened once warm for those type of emissions. Sometimes the the vac hose has a split or it's seized shut. If this happens then it's just like blocking the exhaust up.

On the overboosting issue, I don't think your car has the chance to even boost does it? If it does then it could be overboosting then the ignition cut off switch is cutting the ignition until boost levels come back down. You would be able to see this on freescan whilst driving the car. I don't think it's this problem unless your car does have the chance to boost?

David Walters

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sanj, according to the manual, "The system operates at anacceptable pressure range of 30.5psi - 55psi depending on engine conditions while running"

We are idling at 50psi... Well within range.. Are you thinking that is still too high within the acceptable limit?

Chris

Yes. The fuel pressure regulator decreases/increases the fuel pressure in response to vacuum/boost conditions in the intake, so I would not expect to see such a high pressure at idle. It should be reasonably easy to check -- disconnect the little hose on top of the regulator and apply either a vacuum or pressure to the regulator -- the fuel pressure should change accordingly. BTW, if any fuel is leaking out of that port you definitely have a bad regulator.

You'd expect it to be at the higher end when idling as the pump is running but not much flow.

Not so, as the pressure regulator should bypass the excess, returning the fuel to the tank via the return pipe.


Visit Sanj's Lotus Esprit Turbo SE pages

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Andy,

At idle (high vacuum) the vacuum is applied to the fuel pressure regulator diaphragm, offsetting the spring pressure and resulting in lower fuel pressure and indicating proper regulator control. (From the Service Notes section EMH4)

With the engine off and the fuel system charged it should be 40-47 psi and drop 2-10psi at idle.

The fuel pressure increases as demand increases.


1995 S4s

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As Sanj said, the fuel pressure will rise and fall with the manifold pressure. The vacuum hose from the manifold will cause this. The pressure does no have to be in its limit to return fuel to the tank. The idea is to maintain approximately the same pressure drop across the fuel injector pintle. Makes calibrating the fuel map in the ECU much simpler. That's why the manual gives an acceptable pressure of 30.5 to 55 psi depending on running conditions. At idle you have about 0.6 bar vacuum and, say, 1 bar pressure at full boost giving a 1.6 bar range giving a fuel pressure range of 1.6 bar or 24 psi. Sounds like your fuel pressure is off and you are flooding the engine when you open the throttle. Run Sanj's test to check the regulator function and check the hose from it to the intake.

Always try the simplest and cheapest things first.:wub:


S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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Well, we are still not out of the woods.

Installed the new O2 sensor on the car Saturday, and we are not getting any major improvements that I can tell. There does seem to be a small improvement in the stalling when hitting the accelerator, but it does still hesitate for a brief second. It is still running very rich, there are emissions coming out of the exhaust, and the car still has a slight misfire throughout all ranges. Freescan is still acting the same as it was prior to the O2 swap over. One thing that it is doing now that it was not doing before I swapped the O2 sensor is backfiring. The higher I rev the engine, the more it backfires when I let off the accelerator. Its not a load backfire, but "popping" sounds when I let off the pedal.

I did log a couple of runs on Freescan that everyone can take a look at. I only have the available room to upload one of them. Maybe you can see something I am missing. One of the scans is when the car was sitting at an idle in my driveway, and the one that I attached is during a 5 minute drive around my neighborhood. I also attached a

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Does anyone know a place I can send this ECM to get it tested???.. I posted this question in the ECM/Freescan Forum, but did not get a specific response...

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Does anyone know a place I can send this ECM to get it tested???.. I posted this question in the ECM/Freescan Forum, but did not get a specific response...

Hi Chris..... Were you ever able to figure out the problem with your hesitation/stalling issue on your 1990 Esprit? My 1991 SE is starting to show the same signs of hesitation during take-off from standstill. I just ordered a new O2 Sensor and am in hopes that this will correct the problem. I have also read that I need to clean the flywheel sensor, as it is related to what the computer uses to adjust timing. Any feedback you have would be great.

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