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Discussion Starter #1
Hey everyone,

The car started to develop a stumble. It had done it once or twice before and I attributed it to bad gas (the car). Now it's really bad, and consistent.

It's the worst under load, but has also stated sounding really bad while idling as well. Revving under an idle used to be smooth, and has now developed into stumbles as it tries to rev.

When you first start the car, any throttle at all and the car will almost die... RPMs drop, let off and she'll go back to an idle.

As you drive, it takes a long time to build RPMs, and if you're easy on the throttle while driving she hesitates and stumbles, and I can watch the boost gauge quickly bounce up and down (from about 0.1 to .25 bar). If I get on it (basically floor it), she clears up and builds boost, speed, and does it smoothly.

Any thoughts or experience? I originally thought it was the turbo because it would only act up under load, but now I'm thinking fuel because it does it even at an idle? Vacuum? Or is it one of the Ktronic injection sensors?

Thanks everyone,
Rob
 

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It sounds almost exactly like mine, and I still haven't figured it out. I picked up a wide band 02 to look at A/F ratios as temperature goes up in an attempt to diagnose a sensor, but haven't gotten that far yet. It's definitely not the turbo unless the chra competely locked up blocking all exhaust flow. Have you checked your potato valve? Blocked exhaust could cause the symptoms you're describing.
 

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Does it smell? Does going over a big bump change anything? A sulfur smell would say a deteriorated catalytic convert. It could be a bad muffler. Either of these items that has the internals come apart could do this. Do some simple checks like looking at exhaust, pulling plug wires.

At least you are close to Ralph at RS Motorsports. He is the Esprit guru on the east coast.
 

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Make sure the frequency valve is buzzing. Make sure you don't have any vacuum leaks. You may need to have the injectors cleaned. You may also have a bad/contaminated O2 sensor. Do not mess around with the mixture screw to try to "fix" things. That screw and the mixture cannot change by itself. If it was OK before then something else changed to mess things up.
David Teitelbaum
 

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Just a thought - Isnt there some potential issue with the "clip"(is that what its called?) that holds the rotor in place that can break or loosen that would cause stumbling(messes up the ignition, of course)? I know that in my cars service notes, my previous owner had this happen and the effects he described match yours somewhat.
 

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Integrator
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Discussion Starter #8
I'm agreeing with all these suggestions, thanks for all the help so far. Fuel filter is definitely high on my list, I'll be doing that next weekend. The fuel pump is loud, I never really paid attention to it before but don't think it should hum so loudly.

Keep the ideas coming! Been reading my service manual this morning as well for other things to consider.

Thanks again.
 

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Integrator
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The pump is loud because it is grinding rust flakes.
Don't ruin it!!!
They aren't cheap. Don't run pumps untill you flush the tanks and change filter.
Follow appropriate priming procedure before any attempt to start the car.

Here is my "catch in the pan".
Use non-ethanol gas only to slow down tanks corrosion. Here is a handy web-locator for gas station near you:
ethanol free gas stations, just choose your state:
Ethanol-free gas stations in MD

In addition, to protect the pumps, you should install an in-line filter/strainer in front of the primary pump. I fitted Earls Performance 230210ERL Fuel Filter,
85 Microns, -10 AN Male Inlet/Outlet.
It has to be cleaned once a year untill your tanks perforate and you'll replace them with alloy parts,
or... you sell the car.
 

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Wingless Wonder
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What is the prime procedure for the pumps?




The NYC metro area does NOT have any non-ethanol stations, polluters that we all are! :panic: Don't worry though, soon the ocean levels will rise and put us out of our misery. :rolleyes:




The Bosch pumps are often kinda loud. Not necessarily a problem, but I would check fuel pressure. Be sure to check the integrity of the fuel pump relays and their connectors. These can "melt" if they draw high current.
-eek-
 

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What is the prime procedure for the pumps?

The NY metro area does NOT have any non-ethanol stations, polluters that we all are! :panic: Don't worry though, soon the ocean levels will rise and put us out of our misery. :rolleyes:

The Bosch pumps are often kinda loud. Not necessarily a problem, but I would check fuel pressure. Be sure to check the integrity of the fuel pump relays and their connectors. These can "melt" if they draw high current.
-eek-
There are some ethanol free stations aroune me in upstate, NY but the Octane is lower for some reason so I tend to stay away. I just use Lucas Fuel treatment or some Sta-Bil here and there. The best thing you can do is DRIVE your car and burn the fuel before it goes bad. ;)
 

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Some pumps are just louder than others. They do tend to get louder as they get older. If you are making it pull harder because of a dirty pre-filter it will make it even louder because they do not like making a high vacuum. The crud in the tanks is a big problem. If you are seeing a lot of it the only real fix is to have the tanks cleaned and lined. Putting filters on will protect the fuel system but eventually the tanks are going to rot through and leak. No filter is going to help with that!
David Teitelbaum
 

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Discussion Starter #14
It's not the fuel filter. Took off the fuel pumps, accumulator, and fuel filter. Fuel flowed through all of them and the fuel that drained out of the tank was clean. Changed the fuel filter too.

Also checked the ignition timing. 15 deg BTDC, according to the manual, and does advance when revving in the engine in the garage. The screw clamp for the rotor was not loose.

Next to check is the warm-up regulator, frequency valve, low temp switch...
 

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Wingless Wonder
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Bosch FI Esprits only used the the vacuum advance capsule to boost idle during warmup. If you are not seeing advance at that time, it could be why your engine almost dies at startup.

Your observation of the boost gauge readings would lead me to suggest an inspection of the wastegate diaphragm. Simply ( :rolleyes: ) remove the four 10mm bolts under the WG perimeter...no need to dismount the entire WG from it's manifold.


Be careful of the springs inside! (Ever had a Can-'O-Snakes when you were a kid?)
Snake nut can - Wikipedia, the free encyclopedia :wallbang:

rotfl
 

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I had similar issues with my Jag. I traced it to the ignition. If your wires/plugs are old, I'd replace them. Also, test the coil to make sure it's not dying.

A weak spark will cause stumbling and performance issues like you describe. The fact that you get it at idle when fuel starvation is not likely to be an issue leads me to suspect there may be an ignition problem.
 

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Discussion Starter #18
Bosch FI Esprits only used the the vacuum advance capsule to boost idle during warmup. If you are not seeing advance at that time, it could be why your engine almost dies at startup.
I should explain more. The distributor cap vacuum advance gets "throttle edge vacuum" from cylinder #4, thru a port on the intake manifold. I'm getting erratic vacuum on that port (basically no vacuum), and therefore the timing doesn't advance when you accelerate.
 

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I should explain more. The distributor cap vacuum advance gets "throttle edge vacuum" from cylinder #4, thru a port on the intake manifold. I'm getting erratic vacuum on that port (basically no vacuum), and therefore the timing doesn't advance when you accelerate.
Define Erratic. Wavering, or sometimes ON, sometimes OFF?



Mark ("Amanda") found a missing restrictor in that line, I believe. If your vacuum lines are not original, it could have gone missing.





If base ignition timing was set with a vacuum applied to the dizzy capsule, it is not set correctly. :shrug:

I'll stick to my original statement: There should be no vacuum advance on the distributor when the engine is warmed up. No mechanical either... at 3500 RPM, the timing should be the same as idle on Bosch cars. Block the dizzy's vacuum port to verify.


Rob, if I haven't already, send me an email and I'll send you a scan of the Lotus Cars "Esprit Service Tips" from 1998...




:popcorn:
 

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Checked injectors, plugs, wires, coils?
 
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