The Lotus Cars Community banner
1 - 10 of 10 Posts

·
Registered
Joined
·
606 Posts
Discussion Starter · #1 ·
What would contribute to my Lotus starting to sound like a two stroke sometimes? Here are some details:

Rev250 kit, MP62, upgraded injectors, all Radium stuff, Walbro 255, brand new spark plugs (BOE recommended ones with proper gap).

Last night I went to start up the car to go to the hardware store, and it was running lean at idle and sounding like a two stroke when revving up (revved slowly). I pulled the coils/plugs to check that something had gone wrong as I had recently changed the plugs a week earlier. I also cleaned the MAF just to try and rule that out. Car started up and ran perfectly fine. Just thought of it as an anomaly. Drove to the store and back with no issues.

Drove the car into work this morning, again no problems until I pulled into the parking lot. After showing my badge to the guard the car started sounding like a two stroke again. Brapbrapbrapbrap kind of sound. AFR was showing 16-17 while puttering through the lot. As I was turning into another lot the car died, since I had some momentum I just pop-started it in gear, and now it is sounding just fine again as if nothing happened.... :confused:

So gurus.... where should I start?
 

·
Premium Member
Joined
·
1,413 Posts
check injector connectors. if one is loose it can cause the car to sound like a Suburu.
 

·
Registered
Joined
·
606 Posts
Discussion Starter · #3 ·
Round 2:

On the advice of Radium Engineering, I did their update kit on the fuel surge (new hoses and electrical connectors) as well as dropping in a brand new walbro pump that I had laying around for my rally car. Took a while as soldering new connectors was a PITA, but got it done. Buttoned up everything and took it for a spin.

Ripped on it for 10-15 minutes, redline and everything. Felt great. Then as I was in a cloverleaf to get on the highway it started doing the same thing. Stayed in the cloverleaf and drove another a half mile to a parking lot. When I pulled in it just went right back to normal.... Drove another 10-15 minutes back home without a single issue.

Now wondering if it is something heat soak related....

Urgh.
 

·
Registered
Joined
·
2,309 Posts
i could image "heat soaked" making things go rich?
could lambda sensor or connectors could possibly make for lean condition?
 

·
Registered
Joined
·
606 Posts
Discussion Starter · #5 ·
Checked all the injector connects. Disconnecting them one by one. They are on tight.

Problem is pretty much consistently starting 10 minutes after I drive. Or right as I pull into work, or right as I pull into my garage at home. No CEL. MAF was replaced by previous owner about 15,000 miles ago

When it is idling and doing the babababap thing, it is swingly wildly from very rich back to very lean. Anyone know what else contributes to the fueling as far as sensors go on the Lotus ECU? MAF, O2, TPS....

Driving me nuts, and really making me frustrated with the car, just waiting for it to start losing power on me and go lean anytime I am driving. Becoming hypersensitive to every change in pitch with the engine...
 

·
Registered
Joined
·
2,309 Posts
Well the engine is responding to the ECU, which responds to RPM, TP, and Lambda.
There are likely failure modes where the lambda goes bad when the sensor gets hot, but I do not know for sure.
I would start with the Lambda sensor and wiring.

It is possible that fuel pressure could contribute.
 

·
Registered
Joined
·
577 Posts
Given that you are in open loop until the O2 sensor(s) heats up, I'd start by looking there, though you really should be throwing codes if they've gone bad.

Sounds like now it is happening after 10 minutes every time. If you shut it down and turn it right back on does it run fine for 10 more minutes?

Does it go bad if you just run it for 10 minutes in the driveway, varying throttle? If it only has a problem when you are the road is it really a 10 minute thing or is it environmental, like going around a corner in a certain direction or going over a speedbump. If that was the case you are probably looking at a short.

Would be interesting to see what happens if you force it to run open loop by unplugging your O2 sensors. You'll throw a code and run rich, but if it stays consistent that'll give you an idea of if it's the O2 sensors. In theory you could do the same with your MAF sensor.

If you've got a fuel pressure issue you kind of need to have a fuel pressure gauge to check it out. Sounds like you have the Radium surge tank, so should be pretty easy to add a gauge to your system.

Heat soak wouldn't case things to fluctuate, depending on the tune it could make it consistently rich to compensate for the high air temp in order to lower the chance of detonation.

What about your electrical system as a whole, are you kicking on something that is drawing crazy high amps (or a un-fused short)? What about a loose ground connection? Either of those can cause really weird behavior.
 

·
Registered
Joined
·
606 Posts
Discussion Starter · #8 ·
Did find one of the hoses from going from the end of the fuel rail back to the regulator was leaking a little bit. Ordered a new set of hoses from Radium yesterday. However even when I can get it to leak at idle it won't respond like it does when the problem comes on after 10 minutes or so.

I also pulled my plugs and coilpacks again yesterday, checking inside everything. Found a little scrap of paper towel in one of the coil packs that had grease on it. Must have found its way on there from my socket maybe. Thought ahaa, this is it. Stupid, but has to be that. Didn't have any problems going to work this morning. But as I was pulling up to my house on the way home, babababababa, and died idling in the driveway. So no dice on something dirtying up the coilpack...

:thwack:

Will try and unplug the O2 sensor to see if that forces it into an OL or failsafe mode. It'll pop a CEL I know, but if it stops sounding like it does then might be onto something. Logging showed STFT's to be around +/-5% at idle which is usually fine. However during cruise it does seem to swing quite a bit more than usual (dips into the 13's, goes into mid 15's while hunting for 14.7). The AFR gauge seems to show a large swing with tip-in and the ECU seems confused what to do when I let off the gas and coast. Hovers around 2k before settling down and I can see the AFR gauge hunting.

Rally car should be fixed this afternoon (fuel pump issue, go figure) so may just take that to work and back until the new fuel lines show up for the Lotus.
 

·
Registered
Joined
·
606 Posts
Discussion Starter · #9 ·
So I ran the car this morning with the O2 sensor unplugged. Wouldn't throw a CEL since it has to go through two trips. I expect it to throw the CEL on the way home. However it did default to around 13.9 target AFR instead of aiming for 14.7, so I was confident it was in a failsafe mode.

Drove to work, everything seemed good, felt smoother, but might have been a placebo effect really. As I was nearing work and nearing the 10 minute zone, I got a slight 2-3 second run-up where it was leaning out to 17-18 AFR while cruising at low speeds. Then it just hiccuped and went away. Thought to myself, hmm... maybe the O2 sensor was picking up the hiccup from the slightly lower fuel pressure, then caused the STFT's to go crazy, and that's why it'd then stay sputtering for minutes at a time.

Then as I was pulling into work, it started doing what it always does. I got it into the parking spot and sat there for a few minutes. Was able to snag some video of the sound and such. Unfortunately the second time I blipped the throttle, the issue cleared itself up and went away. You can see at the beginning the AFR is just sitting around 17 or so. Then after it clears itself up, it hangs out at the upper 13's since I have the O2 sensor disconnected.

Lotus fuel issue - YouTube

So now if the new fuel lines that arrive tomorrow, don't do anything. I am completely at a loss. Maybe will just try a new MAF. :shrug:
 

·
Registered
Joined
·
606 Posts
Discussion Starter · #10 ·
Just wanted to update that the issue is solved. New fuel lines from Radium to replace their cracked and leaking fuel lines solved it. My thought is that after 10 minutes or so, the radiant heat from the engine started to soften the rubber hose enough that it created a small leak, so fuel pressure dropped, ran lean.

Now to get my new headunit in, and my interior back together after leather wrapping!
 
1 - 10 of 10 Posts
Top