The Lotus Cars Community banner
  • Hi there! Why not register as a user to enjoy all of the benefits of the site? You may register here. When you register, please pick a username that is non-commercial. If you use a name that appears on any search engine commercially, you must pick another name, whether it applies to you or not. Commercial usernames are for supporting vendor use only. If you want to become a supporting vendor and grow your business, please follow this link. Thanks!

Esprit S4s engine running rough

17K views 92 replies 18 participants last post by  uklad99 
#1 ·
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.
 
See less See more
#2 ·
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.
 
#3 ·
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.
David Teitelbaum
 
#6 ·
@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.
 
#8 ·
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.


Sent from my iPad using Tapatalk
 
#9 ·
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.
David Teitelbaum
 
#10 ·
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. :surprise:-eek-:wallbang::wallbang::wallbang:

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.
 
#11 ·
@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 $$$ :crying:
@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. :thwack:


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

 
#13 ·
@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.
 
#15 ·
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/case-studies/low-speed-abs-fault
 
#17 ·
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.
 
#21 ·
That's the crank-case breather.
There should be a one way valve (check valve) between that and the Tee at the manifold, so a leak there shouldn't cause a manifold leak... if the check-valve is working. I once bought a new check-valve that was leaking and caused a horrible squealing noise to come out of the engine air intake! It was intake cam noise being amplified by the intake tubing.

This noise could be heard from 20+ft outside the car!
https://drive.google.com/file/d/0B2nifoCpaFSfeDNsTmVzWV91eEU/view?usp=sharing
 
#22 ·
In the pic, you can see that the hose coming from the tee (going through a 1-way check valve) to the green thing (crank-case breather?) is sheered off at the crank-case breather in the picture. So I guess I'll request one of those green thingies. along with a new one-way check valve because I can blow through it both directions. I'm thinking of naming the car "Red Devil." It's little pitchfork is always digging in my wallet to make sure I'm forking out some money on it. >:)
 
#24 ·
Yes, there should be a vacuum line coming off to a 'T' (the crankcase breather valve connection) then on to a one way valve, (note black side toward crankcase breather valve connection), then on to the green thingy which goes on to the air filter housing. I can see one end of the vacuum line from the 'T' in your pic. I can see what looks like the edge of the one way valve in post 19 just under the chargecooler with the line running towards the green thingy. What looks like is broken in the other picture of post 19 is an adapter to be able to connect the small hose to the much larger end of the green thingy, (technical term).:grin2:
 

Attachments

#25 ·
Oh geeeeezzzzz.... yes a hose is supposed to be attached to that fuel pressure regulator... if not then that would be a intake manifold leak!!!!
It's the hose from the tee in the manifold that also goes to the crank case breather.

Your green crank case breather looks fine, but there is a white adapter that goes in there that often breaks. You'll need that hose reducer, but you can buy that at any auto parts store.
 
#26 ·
Oops. My bad. Yes that was attached and I removed it. That was the hose in the pic above that had the worn down spot.

Yeah there was a little white adapter that went into the green crankcase breather. The adapter is a parts store item? Woohoo!
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top