3k flat spot and more

[Drfatz]

I am in the final phase of sorting out my project and have managed to get the engine running quite well. However, I still have a flat spot at 3k even though I am running a custom high performance chip from WC Engineering as well as a totally new fuel system (injectors, regulator AN -6 lines) as well as new Lotus plugs, wires and MSD coils and an adjustable cam gear. I have fitted a wideband O2 sensor custom exhaust and a large gt3071r turbo...yet the flat spot persists! Does anyone know what causes this flat spot? Is this something I could eliminate by having my ECU custom tuned for my setup?

While I am on this topic I should mention that she has a bit of a hesitation/stumble right before boost starts to really come on around 4k.

Finally, she also has a very cyclical surging that exists through all rpm ranges. It feels like she pulls a little then backs off a little then pulls a little then backs off again. I would say the frequency of these surges is 2-5 seconds apart and it happens all the time regardless of how much load the engine is under or how much throttle or rpm. Any ideas?

Cheers,

Graham

[Paula&Marcus]

Hi Graham,

Im not sure if your 3k-stumble actually is the same 3k-stumble like almost all 4-Cylinder Esprits do have.

If it is, then it has two possible causes I know of so far ...

1. The base stock code is actually doing this, because of a bit too lean fuelling in this 3k area (= the efficiency tables are a bit too lean in this region). Solution: There is an improved base code available. You should get this one.

2. The standard/stock/old primary fuel injectors also have problems in this region. We found this, because cars that have had very noticable 3k-stumble did not do this anymore when new inhectors have been installed. Solution: Try new primary injectors (Bosch or AC are fine) around 370cc.

Cheers

Marcus

[Drfatz]

Thanks Marcus for the input. I have the upgraded S4s code coupled with a high power WC Engineering chip as well as RC racing primary 370 injectors and RC racing secondaries. I guess I will have to get her on a dyno and see what the problem is.

[t70]

Marcus... you have to be cautious about the injector. John Welch is the only guy out there that I know of who has ensured that the RC fuel injectors that he has made have the same pintle weight as the stock injector. If you replace your stock injectors with "off the shelf" 370cc injectors you will most likely amplify the problem with the "throttle tip-in map" that Graham is experiencing. I'm sure you know how this map works, and how important the injector sizing and pintle weight actually are. Initial tip in mapping has always been a problem with this ecu, but let's make sure Graham gets the injectors that will actually improve the situation... not make it worse.

Edit: I see you've got the right injectors already Graham.

Edited June 6, 2008 by Mark T-C

[Drfatz]

Its funny you mention the throttle tip in map Mark, I noticed that the car has a very slight sluggishness when you first touch the throttle. Its not terrible but I do notice it. I was wondering if this is just a function of the old GM ECU. I am beginning to think a new engine management system may not be a bad idea for the future.

[Gasman GT3]

This sounds like a problem I had with my GT3, and the solution was simply a mis adjusted wastegate capsule. I got quite a stumble where the boost SHOULD have come in at about 3000rpm, then some boost at about 4000rpm. I got it properly set up at my freindly local Lotus dealer and the differnce is amazing, boost from just under 3000rpm and very little turbo lag. I find it's usually the simple things.

[t70]

Edit 2: I'm fairly sure that John Welch has an updated "throttle tip-in" map for the Esprit... He and I had a chat about this problem before -- I thought it was a faulty map sensor causing the problem, but the map sensor isn't even used on initial tip-in... it's how much the throttle position changes within a certain amount of time that is used to determine what fuelling/timing to use.

You're "surging" is almost certainly because of your turbocharger upgrade. I should know how to solve this... but I don't..

John has fully "hacked" the S4 engine management software, so he can solve any of your problems..

The surging... yes.. you're right... couldn't think of it at the time.. but that's the problem... you're wastegate is too small. You need to either install an external wastegate or bore out the wastegate port and put on a bigger flap.

Artie and I have also been discussing "hacking" the original map to help those of us on the forum that have gone a little bit beyond the normal upgrades.

[Drfatz]

I actually just got finished porting the he$$ out of my wastegate you can check out the topic here if you would like,

porting I also installed a much larger and stronger forge waste gate actuator with a 20 psi spring. Funny thing is I noticed the cyclical surging even before I ported out the wastegate. To me is feel like the car is either slightly cutting fuel or timing and then bring it back up. I should mention that the surging is very hard to feel unless your the one driving. I have had several people ride in the car with me and they don't notice it, perhaps I just have a more sensitive a$$ :-p

As for "hacking" the code. I was literally just on the phone with a few local engine tuners in an attempt to get her on a local dyno and resolve these stumbles. I would be extremely interested in helping crack the standard code to allow us to tune ourselves. I have quite a bit of programming under my belt and am reasonably good with electronics. Let me know if there is anything I can do!

Edited June 6, 2008 by Drfatz

[t70]

The difficulty is to see how the computer is reading the map and what part of the map it is reading. I'm sure you know all this already, but there is no "disassembled version" of the file available. John has desassembled the file but will not give us the full version for his own reasons which i respect. He will, however, assist us in our mission. Tunercat has a program to assist with the dissassembly which would be a good investment. The total cost of the tunercat system along with the "Pocket Romulator" by Transtronics should be less than $500. However, the time you'll have to invest will be immense I'm sure. The tip-in map would be nice to have fixed though... if you watch your AFR's on the wideband... they get as high as 17 on initial tip-in.

As for you're surging, you may have too strong of a spring on your wastegate, or you may need to adjust the wastegate actuator slightly... also -- are you using a BOV? Some BOV's can leak under boost, which would cause some surging. However, the tuning will cause the same effect... as you know, maps are "interpolated" and therefore as the computer is moving from square to square and "interpolating" the image, it may encounter odd variables in timing/fuelling at certain boost levels. Don't forget that MAP based computers don't respond well to modifications without re-tuning... things like spool time, exhaust back pressure etc... will change the fuelling significantly.

[Drfatz]

Cheers Mark for all of your inputs. I am seriously thinking that in order to get my project up to perfect running I am going to have to custom tune it, there have just been to many things changed. I am curious if the Lotus ECU code is anything like other GM codes for I know plenty of people willing to share their info on older GM ECUs. I am going to start seriously investigating this. Perhaps we should all combine our efforts over the forum and collectively deconstruct the stock ECU code so that everyone can have access to it.

[t70]

That, infact, was our plan. Artie blew his engine though.. so he's not on board with the project for a couple of months I don't think. I would spend the money on the idea, but my car doesn't have the delco system. I have considered upgrading to it though. I am certainly willing to lend as much assistance as I can though! If Aerobats car doesn't sell this summer, then I may take it upon myself to tune it over the winter (depending on Johns feelings on the matter).

[ozontour]

I had a similar problem and my local guy here at Brisbane tuning and Turbo, Jophn, adjusted the wastegate actuator and sorted.

Now i get a nice clean boost, (10.5lb) from about 2850 and it keeps constant.

I did have a new wastegate fitted at the same time, which I think might have added to the consistency/ continuity of the boost, but it is better than it ever has been prior.

John said that they did not use this wastegate on many cars as there were better ones available on later models that gave less issues.

I went for an after market one, http://www.sellmefree.co.nz/Main/ListDispl....aspx?R=2982381

Goodluck.

Justin

[Drfatz]

My biggest problem with my waste gate right now is that I may have ported my turbo to much and now I have to run such a high spring rate in the waste gate actuator in order to keep the flapper valve shut that the boost pressure on the actuator diaphragm has little to no effect on controlling the boost I may just bite the bullet and purchase another turbine housing and this time port it out only a little bit!

As for the tuning I certainly don't want to step on anyones toes (Marcus or John), but I would really like to learn how to program my own ECU. I am going to make some calls locally and see if I can't find out if the Lotus ECU uses the same logic as the late 80s early 90s GM ECU since it has the same basic computer. There are certainly plently of guys around me who tune the early GM Delco systems however, knowing Lotus they changed something in the way the ECU reads some of the sensors so its all screwy. We shall see!

Cheers,

Graham

[Tony94S4]

Graham,

when I bored the housing I had the same problem,

slow spool up, hesitated, could not hold boost

I found out that the flaper was getting stuck open a little

not sure where it was catching exactly its been few years now,

so I debured the flaper edges and the turbine housing hole

edges and the gate closed completly,

that fixed the problem for me

hope urs is a simple fix to

good luck

tony

[t70]

Graham... There is no other code that is the same unfortunately... I'm sure there are codes that are similar... but the lotus code is definitely distinct. Experience with GM ECU's would be IMMENSELY helpful though.

[Vulcan Grey]

Marcus... you have to be cautious about the injector. John Welch is the only guy out there that I know of who has ensured that the RC fuel injectors that he has made have the same pintle weight as the stock injector. If you replace your stock injectors with "off the shelf" 370cc injectors you will most likely amplify the problem with the "throttle tip-in map" that Graham is experiencing. I'm sure you know how this map works, and how important the injector sizing and pintle weight actually are. Initial tip in mapping has always been a problem with this ecu, but let's make sure Graham gets the injectors that will actually improve the situation... not make it worse.

Edit: I see you've got the right injectors already Graham.

Mark,

The RC injectors are Lucas injectors and do not have a pintle. They use a rotating disc design. The original Rochester injectors also do not use a pintle, they use a ball and socket design. So the "pintle weight" is not the same at all. The Lucas disc is .4g and the pintles are ~4g.

As far as I know I was the first to use BOSCH injectors in my Esprit SE. I found a source ( www.fiveomotorsport.com ) and informed the owner Bruce of the correct injectors to be used in a Delco injected Esprit.

The BOSCH injectors work very well in the Esprit, and are half the price of the RC's. RC will even admit that the BOSCH injectors are very good, though they stil like their Lucas. They do sell Bosch as well though.

Edited June 8, 2008 by Vulcan Grey

[t70]

Interesting... I did not know this... Thank-you Travis... however... there is still an injector "latency" to contend with isn't there?

The issue is not really about that though... my diagnosis as to the 3k stumble is more about the turbo charger upgrade amplifying the problem. The initial tip in doesn't monitor air pressure and because there is a higher volume of air being delivered by the upgraded turbo than the ECU is expecting, then the amount of fuel delivered is less than necessary.

[Drfatz]

I would have to agree with your diagnoses Mark. I stuck in my wide band O2 sensor and on initial tip-in the car runs extremely lean causing a stumble.

[Riddlemr2]

What are you using for boost control? I had a bad surging issue on my old MR2 with an upgraded internal wastegate turbocharger. I has a single-solenoid Apex-i AVCR which simply couldn't think fast enough to control the boost so it would surge up and down. I switched to a Greddy Profec-b and the problem was solved...best boost controller ever.

[DanR]

http://www.kalmaker.com.au/page3.html

http://kalmaker.hotrodhandbooks.com.au/phpBB2/index.php

This has become popular for tuning the Delco systems here in oz. And the forum is also a healthy source of user info.

[Drfatz]

Fantastic! Thanks Dan. I contacted the guys at Tuner C.A.T.S who were very receptive of the idea creating an ECM definition file for the Esprit. Now I just need to get the necessary hardware for chip tuning.

[Artie]

Graham,

Keep me posted on your progress. I'd love to do this as I'll be capable of MUCH more power with my new engine! and I think the "chip" route may be a bit antiquated at this point!!

Artie

[dodge1979]

I know this is an old thread, but Ive got the 'surging' feel on my S4, new but standard turbo, dumpvalve, upgraded injectors as Travis recomended from five-o-motorsport, ramair mod, sports cat and exhaust, upgraded chargecooler rad for better cooling and electric pump etc....did the cause of this constant on off feel be determined??

[bbarton]

Im curious to find out the outcome of this, I too have this problem which has happened since I owned it (about 7 months). If I am all the way into it I don't notice it as much but if im just cruising around at half throttle or less at 3k it gets a quick stumble or hickup then goes away just as fast as it on. I just put in a new stronger wastegate actuator that I got from espritperformance but notice no difference. I was thinking up upgrading to the rc injectors (primary and secondary) over the winter, so im curious to see if this would fix it or if it is the ecu mapping.

[dodge1979]

Well mine does not stumble,it just a slight smooth increase and decrease almost like im gently blipping the throttle a little. Unbeliever noticed now though that it hasnt done it on my last two outings. Im thinking that there has somehow managedto loose its fuel ratio settings. Its mentioned in freescan that they can be reset to learn again, ie after modifications. I havent reset mine but it seems to h

Ave done it itself.