Rough running 4K+ rpm...now barely idles - LotusTalk - The Lotus Cars Community
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post #1 of 24 (permalink) Old 06-20-2019, 01:01 PM Thread Starter
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Rough running 4K+ rpm...now barely idles

Gents,
Apologies for not updating after buying Dave’s S4S. Got a little busy with summer! Unfortunately I got home and a few days later things went bad. When I bought the car I was advised it was running a little rich. Sure enough I pulled the plugs and put in fresh, stock NGKs (after gapping them). No better. Car still had a hard “stutter” between 3.5-4.5k rpm depending on the aggressiveness used with the throttle.
Called JAE and a trusted new friend in Nashville and got some good advice. I replaced the original HT leads. Car drove a little better but something still felt off. I also nicked a broke the reducer on a vacuum line 🤦‍♂️ Never fear electrical tape to the rescue to get my test drive in. Car still has a hesitation between 4.5-6k rpm depending on throttle aggression.
And now. Today.
I replaced the MSD coils from PPO of unknown age with the JAE near OEM ones. Car will barely idle. If pushed to rev she doesn’t want more than 2-2.5k rpm. I tried swapping leads 2&3. No change.
I know I’m dropping a lot of variables on you guys but I just got my dream car and thought she was well sorted and I’m out of airspeed and ideas. I have two jobs and two kids and I’m not giving up but man is it getting hard for her good looks to overcome the lack of motion.
Thanks for any help gents.
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post #2 of 24 (permalink) Old 06-20-2019, 01:12 PM
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Originally Posted by FelonWaites View Post
Gents,
Apologies for not updating after buying Dave’s S4S. Got a little busy with summer! Unfortunately I got home and a few days later things went bad. When I bought the car I was advised it was running a little rich. Sure enough I pulled the plugs and put in fresh, stock NGKs (after gapping them). No better. Car still had a hard “stutter” between 3.5-4.5k rpm depending on the aggressiveness used with the throttle.
Called JAE and a trusted new friend in Nashville and got some good advice. I replaced the original HT leads. Car drove a little better but something still felt off. I also nicked a broke the reducer on a vacuum line 🤦‍♂️ Never fear electrical tape to the rescue to get my test drive in. Car still has a hesitation between 4.5-6k rpm depending on throttle aggression.
And now. Today.
I replaced the MSD coils from PPO of unknown age with the JAE near OEM ones. Car will barely idle. If pushed to rev she doesn’t want more than 2-2.5k rpm. I tried swapping leads 2&3. No change.
I know I’m dropping a lot of variables on you guys but I just got my dream car and thought she was well sorted and I’m out of airspeed and ideas. I have two jobs and two kids and I’m not giving up but man is it getting hard for her good looks to overcome the lack of motion.
Thanks for any help gents.
If she barely idles after swapping coils then i would double, then triple, then quadruple check the leads, connections and correct orientation of the coil packs and leads. Its also very important to get a good seating on the D.I., which can also fail but as your poor idle came along after changing the coils its more than likely related, its possible to crack the base of a new coil pack if not seated correctly. Also the 4 GM MPFI sustem is a wasted spark system (also know as distributorless or DIS)
No 1 and No 4 are paired and No 3 and 2 are paired but you mentioned you swapped them already. If for example No 3 is misfiring swap the leads for 2 & 3 around at the coil pack. If the fault jumps from 3 to 2 then its the coil pack. If the fault stays with 3 then its the plug, lead or a mechanical/fuel issue with the cylinder. If one injector fails then it will pull down a second injector as the pulses are also in pairs but again this only cropped up after changing the coil packs, not unheard of to get a bad one so try pulling one lead at a time to see if it changes the rpm (tough i know as it wont idle) this should narrow it down to a coil pack or a single cylinder.
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Last edited by esprit888; 06-20-2019 at 01:43 PM.
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post #3 of 24 (permalink) Old 06-20-2019, 02:16 PM
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Any chance you got a tank of bad gas?

I wonder if the black tape fix is still allowing a vacuum leak and affecting idle.

Also, do you have the ability to run the Espritmon or Freescan? I have not had to use them yet but I suspect you can see things in the logging functions that may lead you to the issue. I feel certain its something simple.

Can you describe what happened right before and when the issue popped up? Did you wash the car and get the engine wet or anything like that? (normally not an issue but might give the pros on here a clue).

94 Esprit S4 - Silver
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Last edited by Erik L; 06-20-2019 at 03:07 PM.
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post #4 of 24 (permalink) Old 06-20-2019, 05:36 PM
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Or you could try putting the MSD coils back in and see how it runs. Either you messed up changing the coils or the new coils are bad. Ignition wires can be fragile. The inner core can break if you pull too hard so it is possible you damaged the HT leads. Check with a meter or just try the old ones. Other things to check is the ignition timing and advance and the fuel injectors.
David Teitelbaum
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post #5 of 24 (permalink) Old 06-20-2019, 05:41 PM Thread Starter
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Thanks for the ideas guys.
I’ve got a new vacuum reducer on the way from Joe soon but I did consider the tape not sealing any longer.
No washes recently and I use cardboard to block the engine when I do.
I’m going to try the lead swap again and then perhaps put the MSDs back on if no luck.
Dave thanks for the heads up. I may be asking about the details of timing next. Wishing I was closer to a solid Esprit mechanic.
I do have espritmon and freescan but haven’t properly read up on them to use yet. That’ll be tonight’s homework.
Many many thanks again!
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post #6 of 24 (permalink) Old 06-20-2019, 06:53 PM
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Also search the forum for "stumble" i saw several threads only a few for your years but they all seemed to point toward fuel related issues, pumps and injectors.

you might try resetting the ECU by disconnecting the battery for a while.

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post #7 of 24 (permalink) Old 06-20-2019, 08:18 PM
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I suspect you have the leads connected wrong somehow. FYI, if you are using the manual as a reference, the coil on the S4s is mounted inverted to the diagram in the manual so you could have the pairs on the wrong terminals. Also if you have the wrong pairs together, swapping what you believe is 2 & 3 won't make any difference. Double check all the connections again...

Jim
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post #8 of 24 (permalink) Old 06-20-2019, 10:09 PM
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Rough running 4K+ rpm...now barely idles

Quote:
Originally Posted by Erik L View Post
Also search the forum for "stumble" i saw several threads only a few for your years but they all seemed to point toward fuel related issues, pumps and injectors.



you might try resetting the ECU by disconnecting the battery for a while.


Ditto on the stumble!! You can smooth out the stumble a bit by swapping out the cam gear on the auxiliary side and buying the green dot pulley. Contact your local serviceman if you are not so inclined. Ralph at RS Motorsports in NJ did mine, and it was a nice upgrade. Also...I believe you need do something with the throttle jack solenoid and the EBPV (exhaust back pressure valve). Plugging up one, and disconnecting the other. Just having a brain fart right now on which is which..


Also....go on the Esprit Fact File site ( non Flash version ) and find your way into the index area. You will then be able to pull up a wide array of information regarding the Esprit. Expand and read the “Components” and “Troubleshooting” sub categories.

http://www.espritfactfile.com/indexs.html




Here is an excerpt taken from the index and may give you insight into your issue.

”Why does my Esprit engine rev so high when I cold start it?”
Many people panic the first time they start certain 4-cylinder Esprits with the engine cold. Usually (but not always ) the RPMs climb rapidly to 2,500 or higher. Relax. This is normal behavior. In order to meet federal emissions regulations, the Esprit engine management system contains two components called the Exhaust Back Pressure Valve (EBPV) and the Throttle Jacking Capsule. The purpose of these two items is to bring the catalytic converter up to operating temperature as quickly as possible. This is done because converters don't work well at removing pollutants from exhaust gasses until they are warmed up.
In the simplest terms, this is what occurs: When the engine is being cold-started, the engine management computer (ECM) sends a command that closes the EBPV. This valve is located within the exhaust pipe, at the union between the rear of the catalytic converter and the pipe going to the muffler (silencer). Closing this valve essentially blocks the exhaust, trapping heat which causes the converter to warm up more quickly. While the EBPV is closed the ECM is referred to as running in "open loop mode".

The problem with closing the EBPV is that it has a tendency to cause the engine to stall. If you have seen the movie Beverly Hills Cop, you undoubtedly have heard of the "banana in the tailpipe trick". In order to prevent the engine from stalling, the ECM also sends a command to the Throttle Jacking Capsule which causes the throttle plates to open up (similar to pressing the accelerator pedal). This causes the RPMs to rise and prevents the engine from choking itself. Note You can force the ECM to drop the idle by quickly and briefly stabbing the accelerator pedal at least halfway.

After approximately 2 minutes, the ECM switches to "closed loop mode". It sends the opposite command to the EBPV to force it to open, and tells the Throttle Jacking Capsule to stop holding the throttle open.

The problem with the whole concept of EBPV / Throttle Jacking mechanism is that if you attempt to drive during this warm up cycle, the car will perform like crap because the exhaust is blocked. Furthermore, because the EBPV is spring-loaded to remain normally closed, any failure in the system (like a disconnected vacuum line) will cause the car to drive terribly. Due to this, many Esprit owners have chosen to wire EBPV to remain constantly open, or have removed the valve altogether. To help prevent the annoying high RPMs (which are much louder once the EBPV is wired open), many have also removed or disconnected the Throttle Jacking Capsule. There is nothing wrong with doing this. Remember, this mechanism is only there because Lotus needed it to meet EPA laws in the USA. In fact, when Lotus built the Esprit GT3, it also removed both these components. They were able to do this because the GT3 was never intended for the USA market. Besides, removing these items also reduces vehicle weight which is part of the Lotus religion.

Refer to Technical Service Bulletin #3 for more info on this topic.

Also....here is a link to the green dot pulley....

https://www.lotustalk.com/forums/f16...lley-s-200193/



Hope this helps
Dominick


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Dominick Munofo
Lotus Ltd. Senior Advisor/Past President
1995 Norfolk Mustard Yellow Lotus Esprit S4s:

SS Cat Bypass Pipe, Micklewright Exhaust, Ram Air mod, 104 deg MOP Cam Wheel, HKS SSQV BOV, K&N Air Filter, Carbotech Race Brakes, SS Brake and Clutch Lines.

Last edited by yellow hornet; 06-20-2019 at 11:04 PM.
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post #9 of 24 (permalink) Old 06-21-2019, 03:29 AM
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Hi Mike, I would put everything back the was it was when you bought it and then Check the Cam timing just in case it jumped a tooth. Also I would check the fuel pressure at high RPM . Dave S4s
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post #10 of 24 (permalink) Old 06-21-2019, 12:06 PM Thread Starter
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Checked the cam timing right after we spoke a few weeks ago. All is good there.
I was super careful with the new leads so I can’t imagine they’re dorked up but one never knows. Will be out with my multimeter later.
Everything seemed much better with the new leads so all I could imagine was a high rpm/on boost fueling issue. Dave did a new fuel filter within the last year and not very many miles...and had the injectors gone through as well so all I can figure is fuel pump if it’s not hung up in the ignition or a vacuum line.
Next step is multimeter and ensure I have a good connection and no leaks on that vacuum.


As for the EBP it and all its components are gone from one of the POs so thankfully there’s one less variable to worry with.

Thanks again for the ideas guys. Anything else springs to mind please speak up. Military guy so I’ve got thick skin and my wife says I don’t have any feelings to worry about 🤣
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post #11 of 24 (permalink) Old 06-22-2019, 07:43 AM
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Haven't reviewed the entire thread, but check the fuel pump pressure.

All the GM pumps are starting to fail, now...
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post #12 of 24 (permalink) Old 06-24-2019, 05:27 AM
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Personally I think you are a little beyond just swapping cam gears to fix your issue. As others have said returning the car to the way it was at first is the best thing to do. After that I would check fuel pressure, but I would also check all vacuum lines. Vacuum lines would cause issues as you have described. After that I would check ignition system for faults. I just finished helping UKLAD99 with his car and his symptoms were much like yours. Things we found on his car were fuel injector leads not sitting correctly on the injector (wires had pushed back in the connector and not making contact with the injector even though the plug was connected). Vacuum lines were not correct and lastly a ignition module that would fail as it heated up. A great deal of patience and understanding how the GM efi works goes a long way in repairing issues like this. Remember it is a waste spark system so one injector not working causes two to not work. That is also true with spark, one coil fails causes two cylinders to not work. If you can get the car running at all and pulling a plug wire and seeing if there is any change in the engine will help determine which cylinders are failing.
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post #13 of 24 (permalink) Old 06-27-2019, 11:06 AM Thread Starter
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Ok back from a trip and back in the saddle for a few days. Thanks for the responses.
Putting it back to “the way it was” would only involve the original oem leads that are 24 years old and the spark plugs and coils. I “un-did” the new coils yesterday (msd were on it when purchased) after using my multimeter. Anyone super familiar with why the MSD coils and JAE ones put out drastically different numbers? The JAE coils were 5800 and the MSD were 7800... I need to check the oem specs but don’t have a service manual.
I’m going to keep the new wires and plugs (all oem from JAE) as that is when the car has run best save for the drive home. Other things I noticed were the vacuum line is still sealed from my tape job as I wait for Jae to locate parts. Aaaand there are two wires with no home. Noticed one of them when I first got home from buying it. The other seems to have recently come loose. Could have happened when I was pulling coils.
Anyone familiar with where these two nice wires should be living? 😀
Next up I’m going to get a fuel pressure gauge from the auto parts store and see what I can learn measuring the pressure at the rail?
Should I unseat and re seat the injector plugs with some dielectric? Hesitant as Dave did the injectors and fuel filter recently. Seems the fuel pump is very likely failing due to age and the high rpm demand it can’t keep up with? That’s my best stab at the logic. I did some searching and found where people have done it but no write up. How bad is a fuel pump replacement? 😳
Thanks again for the insight gents. You guys are what makes this community. Plus Her good looks and the bad weather are keeping me sane but man I want to drive.
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post #14 of 24 (permalink) Old 06-27-2019, 08:25 PM
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It seems your picture is showing terminal in alternator housing with a crimp-on connector and wire missing.
The brown wire you are holding... does it have a white stripe on one side?
My S4S has a brown wire with white stripe which has a crimp-on connector and is connected to alternator terminal tab.
(NOT the main positive output connection).

zig
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post #15 of 24 (permalink) Old 06-27-2019, 09:10 PM Thread Starter
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Zig. Yes on the white stripe. I have the insulator and the crimp on connector available. Just re install on that open pole of the alternator?

Thanks man!

As for the other clip on connector with the bundle of wires attached I’ve looked all over for an open “female” receiver. All are spoken for. Weird.
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post #16 of 24 (permalink) Old 06-28-2019, 03:30 AM
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Is that connector near the header tank and the TPS sensor? Does this car have the revised harness?

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Last edited by tmusc; 06-28-2019 at 03:50 AM.
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post #17 of 24 (permalink) Old 06-28-2019, 09:33 AM Thread Starter
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Victory.
So. In summary
HT leads fixed the “root problem”. The car get as if she was surging and did NOT want to rev past 4K depending on the gear. New plugs smoothed a little. New leads did the rest. Unfortunately I screwed up and nicked a vacuum line. After band aiding that with electrical tape while waiting on parts. She worked again.
New coils. Did not help/hurt. My guess is the car is in a slightly elevated state of tune requiring more spark. I have zero evidence to back this up other than PO and PPO and PPPO who did a bit of work consulting with John Welch.
Today I went back to the MSD 8224 coils and keep the new leads and plugs. I mended the curious brown wire I also broke with Zigs advice. The car ran very well. MUCH smoother. Clearly there was a miss due to a wire. No more. I was grinning ear to ear. I was 10 years old again watching Roger Moore make plays on Ringos girlfriend. However she’s not perfect. If I used more than 75ish% throttle I think I’m exceeding the aging fuel pumps capabilities.
So waiting on vacuum lines. Aaaand probably going to take her to my friend TJ when it gets cold outside to make sure she’s perfectly dialed in for next spring.
Many many thanks guys. Truly.
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post #18 of 24 (permalink) Old 06-28-2019, 05:53 PM
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I doubt the fuel pump is what is "holding" you back. A pressure and flow test can help you figure that out. Maybe a dirty filter. Rusty fuel tanks can plug a filter up quick and Lotus's do rust their fuel tanks. Rule that out and I suspect you still have a tuning problem like a bad injector, HT wire, or plug. Vacuum leaks and faulty sensors can also cause loss of top end RPM's. So can valve adjustments, stale fuel, anything that isn't "just right".
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post #19 of 24 (permalink) Old 06-28-2019, 06:02 PM
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Yes, The brown wire with white stripe is connected to a tab on alternator on my S4S

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post #20 of 24 (permalink) Old 06-29-2019, 03:57 AM
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Hi Mike, So glad to hear that the S4s is running the way it should. A coupled of things I question , you said you don't have the service manual? I included it with the sale, also there are a couple of plugs back by the header tank area that went to the deleted exhaust back pressure valve. If you have to replace the fuel pump , it's going to be a real pain in the a$$ because of all the sealer on top of the tank, sorry, on the bright side I did give you a new fuel tank O ring from JAE. Keep up the good work. Dave S4s
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