Esprit S4s engine running rough - LotusTalk - The Lotus Cars Community

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post #1 of 56 (permalink) Old 05-11-2017, 01:59 PM Thread Starter
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Esprit S4s engine running rough

PROBLEM: I'm having a hard time trying to figure this one out. Some months ago, I thought I noticed that the engine would seem a little rough and not much power in 5th gear at 2000 rpm. It was so subtle that I figured the engine just didn't like lugging along in that gear at that rpm. Now it has become so bad that the car is almost not drivable. It seems that any gear around 1700 - 2000 rpms will cause the engine to seem like it has water in the gas. The timing sounds retarded and there is no power.

WHAT I"VE DONE SO FAR
  • Adjusted and set the Throttle Position Sensor to .63v (a little on the high side because I occasionally see a TPS Sensor low voltage error pop up once in a while)
  • Adjusted cable to change the throttle response from 0 - 95% to 0 - 100%
  • Adjusted the IAC adjustment screw to get idle down near the 976 rpm and the IAC position to between 20 - 40 (but the IAC is a continually moving target)
  • Checked the spark plugs and found a lot of carbon on them (none appeared to be running too hot)
  • Removed the air filter to see if that had any affect (nope, it didn't) My thought was that maybe it wasn't getting enough air because the issue is at low idle when there is no boost
  • Reset the IAC to factory defaults
  • Verified that the cams were still aligned (no apparent belt slippage)

I'll post a video and my thoughts later, but thought I would throw this much out there to get the ideas flowing in.

Thanks all.

Jim S.
1995 Esprit S4s
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post #2 of 56 (permalink) Old 05-11-2017, 03:13 PM
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Jim

Try resetting the ECU.

Here's how (copied from my tech notes):

1. Applies to all GM computer 4cyl. First, disconnect the - battery terminal for 15 minutes. Before re-connecting it, touch the + and - terminals together for 15 seconds to dissipate any residual charge.


The recommended way to teach the computer after a battery disconnect is to start with a cold car. Turn ignition on, leave motor off, give throttle pedal a full to the floor travel. Then start car without touching throttle, let it idle till temp rises to 80. While it is warming up keep a load on the motor by running headlight/AC. Once it is warm drive the car moderately for 5-10 miles, then begin more spirited runs.

You might get a few brief overboosts till the computer learns, but everything works well after about 20 minutes.

2. there is a separate learning process for the pulse width boost modulation. I always knew about the idle learn process, but this is a separate process that only happens when in the overboost mode (over 0.65 bar). Basically you have to run it hard several times so the computer can learn how much modulation it takes, so it knows where to start the next time.

Works fine now. Just shy of 1 bar, right where it should be on S4s.

Atwell Haines
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post #3 of 56 (permalink) Old 05-11-2017, 05:24 PM
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If you experience a lack of power at high RPM's it could be fuel flow. Not getting enough fuel at high rates of flow (high speed high power). First things that come to mind are plugged injectors or plugged up fuel filter. Replace the fuel filter and get a bottle of Techron to put into the fuel. If that doesn't help it could be a bad fuel pressure regulator, plugged up filters in the tank, bad fuel pump, etc. What can cause this problem is when the tanks rust inside and all of that rust and dirt plugs things up.
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post #4 of 56 (permalink) Old 05-11-2017, 05:32 PM
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Does the engine stop accelerating past 2,000 rpm? Or is it more like a flat spot and then good above? Will the engine rev freely without a load?

Don
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post #5 of 56 (permalink) Old 05-11-2017, 06:38 PM
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Is the Check Engine light on?
Did you check your O2 sensor? I had similar problem with my car few years ago and a new O2 sensors fixed it.
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post #6 of 56 (permalink) Old 05-11-2017, 08:19 PM Thread Starter
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@carbuff - I tried to simply reset the ECU by pulling the battery cable for about 5 minutes, but I should have looked up the correct procedure to try it. Good point.

@jtrealty - I'm having the low power issue at low rpms (between 1700 - 2100 rpms). Injectors were one of the things that came to my mind too. I forgot to mention that I did replace the fuel fileter (originally done about 2 years ago). I cut it apart to look at the filter to see if I was getting anything weird in it (thinking that maybe those tanks are rusting out, but I didn't see a single flake after running the tanks dry twice in the filter paper).

@CarSalesman - The engine picks up around 2200 rpms and goes like normal. It seems like the engine issue doesn't occur nearly as much with the transmission disengaged as opposed to having the transmission putting a load on the engage. Anything below 2000 and it wants to start bucking like a horse almost.

@lotusespritman - I have seen the check engine light come on momentarily, but that hasn't really been anything new since I bought the car about 3 years ago. The light comes on mostly as I run high revs and then let off the gas with the transmission still engaged.

Various errors I have seen so far during the past few months:
13 - Oxygen Sensor; Open Circuit
22 - Throttle Position Sensor (TPS) Circuit; Siggnal Voltage Low
24 - Vehicle Speed Sensor (VSS) Circuit
24- TIP: A Weak idle mixture or bad misfire can cause this.
34 - Manifold Absolute Pressure (MAP) Sensor Circuit; Signal Voltage Low
35 - Idle Speed Error
35 - TIP: Maybe IAC Valve or bad misfire
44 - Oxygen Sensor Circuit; Lean Exhaust Indicated.


I have been speculating that I have a sensor issue somewhere that is messing up the ECU calculations. I have ruled out the spark plugs since they all pretty much look the same except one might have been running a little hotter than other because it looked like some white build up on the nodes after I cleaned off all of the soot. It is getting air since I removed the air filter, and gas seems to be flowing, although perhaps it isn't getting enough pressure from the sender which I cannot easily rule out yet.Which means I'm down to O2 sensor, IAC valve sensor; and TPS sensor as being possible culprits. Perhaps an new O2 sensor would be the next part to try replacing (hopefully the local hardware store has those).

I'll post the videos soon but they are too big to easily download to YouTube.

Jim S.
1995 Esprit S4s
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post #7 of 56 (permalink) Old 05-12-2017, 03:14 AM
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The mention of fuel pressure is a good one...many GM MPFI cars are requiring fuel pump replacement after 20+ years.


Check fuel pressure or troubleshoot

Here's a related Topic:

93 Esprit: fuel pump whines....walbro replacement?

Atwell Haines
'88 Esprit
Succasunna, NJ USA


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post #8 of 56 (permalink) Old 05-12-2017, 05:32 AM
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Definitely reset the ECU. I used to wait like 20 minutes before reconnecting.

Do you have a BOV installed? Installing one will help with throttle response in between shifts.

Does your car have the ram air conversion? It's a fairly easy mod to do, and will help with getting more in the intake.

Is the gas in your car from when you had the car stored fo the winter. Maybe you have some water in the gas tank? Throwing a bottle of water remover into the car couldn't hurt. E10 gas if not treated with a stabilizer, is only good for a few months before it starts to go south.

While I don't think the above suggestions will fix the issue you have, it may help.


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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.
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post #9 of 56 (permalink) Old 05-12-2017, 06:04 AM
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If you have a sensor issue you should get a check engine light. It is possible you have codes but the light hasn't come on yet, not enough engine cycles so check for any trapped cores. If it isn't fuel flow it could be a problem with your timing advance. Another possible cause is a breakdown of your secondary ignition system. Bad wires or coil.
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post #10 of 56 (permalink) Old 05-12-2017, 06:40 AM
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What can cause this problem is when the tanks rust inside and all of that rust and dirt plugs things up.
David Teitelbaum[/QUOTE]

Nooooooo, not the rusted tanks.

I think I am going to be ill.

I will fix this for you. When the car transporter arrives put the car on and hand him the title. I will end this pain for you.
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post #11 of 56 (permalink) Old 05-12-2017, 07:14 AM Thread Starter
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@carbuff - I'll check out that link, thanks! I'm afraid to go down that path. If I replace the sender units, then I'll likely want to replace the tanks with stainless steel ones $$$
@yellow hornet - I do have a BOV and I converted to Ram Air last month.
@jtrealty - That's what I'm wondering with those O2, IAC & TPS codes that keep cropping up as shown in post #6
@Jenna'sEspritTurbo - yeah. I think you're right. I'll go start looking for the title.


I wasn't able to video capture the actual rough engine during a drive. But here you can see the high idle that it sometimes randomly does. This wasn't even racing as high of an rpm as it sometimes does and gets stuck in high rpms (~3000 rpms) adn I end up shutting off the engine to stop it.
  • The car is already warmed up.
  • I just clicked the Reset IAC button to reset it to factory defaults
  • At 1:31 I rev the engine to kick it into low idle
  • At 1:48 You can see the IAC position start to climb from 0 to 48
  • At 3:10 The car starts into a high idle on its own and starts to go up and down (perhaps this is the ECU learning?)
  • At 4:19 watch the Rich/Lean number take a dive from 254 down to 0


Jim S.
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post #12 of 56 (permalink) Old 05-12-2017, 07:23 AM
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Cant blame for me for trying,, I mean I know red isn't your fav color
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post #13 of 56 (permalink) Old 05-12-2017, 08:46 AM
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@Seraph

Haven't looked at the data yet, but reading all of the CODES that you had stored made me think you possibly had a voltage problem, at least at one time. You might have a loose/bad ground on the engine. Since you recently had the transmission out, check the grounding strap to the top of the engine, and the other one to the motor mount on the right side of the engine.

Since you reset the ECU, I saw some of the codes have returned (35, 35, and 44), those could be part of the air leak in the manifold issue. Your IAC is having trouble compensating for excess air in the manifold, and therefore that also leads to a lean burn at the O2 sensor.

BEFORE REPLACING ANY PARTS, you need to check for an air leak in the manifold. Replacing parts will only confuse the issue.

Clean the IAC O-ring
Check every hose on the routing diagram under the hatch.
Listen for weird valve clatter noises or whistling.

Adjusting the minimum air rate bleed screw should not effect the idle rpm if the IAC is able to operate in the roper range. If you go out of range, then the IAC will not work properly, and the engine drivability will suffer.

The 2000rpm hesitation can be a MAP sensor issue (also could be related to excess air in the manifold), What that means is that the engine is ok to run without load, but as soon as it has any load, then the fuel flow calculations don't work, because the MAP sensor reading is not accurate.

I don't remember if you have the EBPV (Exhaust Back Pressure Valve) below the catalytic converter, but if you do it could be not opening, which can also cause the engine to not be able to rev past about 2000rpm. Ensure it is permanently open, or working properly.

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post #14 of 56 (permalink) Old 05-12-2017, 09:13 AM
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Your Baro is low, due to your altitude (mine is .65 at 5300ft), but not unusual for the Lotus. Your MAP is also too close to the BARO at idle... MAP should be approx 1/2 BARO at idle. This would indicate an intake manifold leak.

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post #15 of 56 (permalink) Old 05-12-2017, 09:17 AM
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Your "Vehicle Speed Sensor" signal may be low or bad due to rust around the sensor or on the sensor rings. Carefully remove the wheel speed sensors (use penetrating oil to prevent breaking the plastic if needed) and clean the hubs under where the sensor mounts, and clean the rust off the sensor wheels.

More info here
https://www.picoauto.com/library/cas...peed-abs-fault

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post #16 of 56 (permalink) Old 05-12-2017, 09:30 AM
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vacuum leak?
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post #17 of 56 (permalink) Old 05-12-2017, 10:09 AM Thread Starter
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Thanks Travis. The vacuum hose that runs near the fuel rail and under the chargecooler might be the issue. I ran my fingers along that tube and I can feel there is damage to it from the sharp edge of the chargecooler rubbing it. I'll have to wait a day until I have time for removing the chargecooler to inspect and replace the hose. I'll update later.
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Jim S.
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post #18 of 56 (permalink) Old 05-13-2017, 11:01 AM Thread Starter
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It was not the vacuum line that was damaged. It was worn, but not worn all the way through to create a vacuum leak. Time to do some more vacuum line tracing.
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post #19 of 56 (permalink) Old 05-13-2017, 11:54 AM Thread Starter
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I found a broken connection on the vacuum line that goes to the green plastic thinga-ma-jig. The plastic connector broke off in the tubing. Does anyone know what this is, where to get one or ideas on how to replace it?
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post #20 of 56 (permalink) Old 05-13-2017, 01:29 PM
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looks like a check valve
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