LS1 running at half power - need some hints

[gjkrv8]

Hi All,

Today took the Cobra for a run and its like somebody turned on a 50% power switch.

Am looking for some hints on troubleshooting (short of taking it to an expert).

Essentially when I accelerate its like its running on 6 cylinders.

Also when crusing along at 100Kph it is rough when you increase the power slightly.

So Far I have checked the following:

1. Fuel Pressure = 59psi - stays the same when you put your foot down
2. Put my ODBII DashCommand etc logger on - nothing of note comes out
3. Checked all plug leads are on tight (one looked a bit suss so I removed and reconnected - no change)
4. Checked all engine loom connections to things like TPS, MAF, etc


The only other things I have done since I last used the car a week ago is that I disconnected the battery whilst fixing my stop light switch.

You havent heard of the ECU going into a weird mode if the power is removed??

Other than that anyone know a good LS1 guy in MElb Eastern suburbs.

Thanks - pls no ford jokes.

Rgds

Gregg

[ICETOO]

Greg, what sort of ECU (or PCM if you prefer are you using).

It is a fair bet that the ECU has hard reset and is now back in learning mode...I am assuming that you have something like the DASH DAQ set up as well. Does this also have any after-market tune maps as well that you load in via the OBD II port. If so, reload the stock ttune then over write with the performance tune.

The ECU will take some time to get the AFR (stoichiometric ratio) right again to run at optimum performance.

Also check that your O2 sensors have not fouled up but the diagnostic on the dashdaq type kit would register a MIL error if significant.

When ever I disconnect my battery on my LS1, or even the XR4 I have the same issue.

This will normally sort itself within 100 kays or so.

Best of luck mate!

[gjkrv8]

Thanks ICETOO - I drove about 90 ks today from Melb to Rye. I have turned off the power to the ECU for a while in case it fired up in a weird mode. I am also going to have a look at the MAf to make sure its clean as I read something about that. Also Can you disconnect O2s and run in Open loop mode to see if the O2s are giving false readings?

Thanks


rgds

Gregg

[DaveW]

Gregg,
Take the potatoe i stuck in your exhaust out......

Sorry mate, had nothing constructive to contribute.

Dave

[sambo]

Sorry to hear Gregg. My misfire problems were eventually traced to a dodgy injector plug that wasn't contacting the pin on the injector properly. Try Erol at EFI Dynamics in Lilydale, he's a tuning wiz and should have some suggestions for you. Perhaps book it in for an hour next week.

Efi Dynamics, Lilydale VIC 3140 - Mechanics - TrueLocal

[gjkrv8]

Dave, I wish it was only a potatoe :-(

Paul thanks for the tip on Erol, will give him a try if I dont find the source of the problem. Am going to have a look at the fuel filter to check its ok.

Further testing shows that its only when I plant my foot it sort of dies. If I use light throttle it seems better, so maybe fuel starvation due to blocked filter. Although the fuel pressure guage is after the filter so I would assume pressure would drop if that was a problem.

Anyway - the process of elimination continues.

Rgds

gregg

[boxhead]

The ecu does lose memory after being disconnected, but mine relearns within minutes, I get a low idle till it relearns.
Probably need to determine if it is a miss or a lack in power before trying to go any further.

[ICETOO]

Originally Posted by gjkrv8

Thanks ICETOO - I drove about 90 ks today from Melb to Rye. I have turned off the power to the ECU for a while in case it fired up in a weird mode. I am also going to have a look at the MAf to make sure its clean as I read something about that. Also Can you disconnect O2s and run in Open loop mode to see if the O2s are giving false readings?

Thanks


rgds

Gregg

Still reckon the ECU may need a good run to relearn. Sometime when the independent power supply to the EPROM in the ECU jags in the tuning map and codes can be lost. Do you have you original tune loaded into your dash controller unit or hand controller unit what ever the case as you can reload the tune and go from their.

We are assuming here that you have done checks for uptake restriction and vacuum leaks at the intake. This will normally show as a MIL error from the MAF datum series of P codes.

If you do have a dash unit or and OBDII interface with a PC or I pad, you can assign a driver to the O2 sensor in the analogue drivers menu (of most tuning suites and controllers) to ascertain what lambda signal value is being read by the ECU...this will directly influence injection metering, timing ans the fuel intermix ratio.

You can also a sign a driver to the secondary O2 sensor downstream of the catalytic converts if fitted....and compare the two values. I think running the O2 sensor in open circuit will not give any real data as the ECU will have to run of the secondary if fitted with the primary bypassed...but may also help narrow down the gremlin...but I would expect if there was no secondary the ECU will become even more confused.

Another thing to check is fouling of the Manifold absolute pressure and temperature (MAPT) sensor. These pick up junk from either PCV or EGR recirc systems when the engine cools and the condensate forms a sludge that will effect the voltage potential on the sensor and thus send incorrect data to the ECU to manage....and poo data in equals poo direction out.

Worth a quick pull, look and tizzy up with some electrical contact cleaner.

Lets us know how you go mate..Ads!

[Modena]

Gregg from memory you have a stock tune. As has been said, when the ECU goes into learning mode after being reset (either by loss of power or manually), you need to start it and let it idle for about 10 mins, then drive it and FANG THE CRAP OUT OF IT for about 10 mins. It then learns a nice power delivery map This always worked for me in my SS LS1 years ago.

Failing this, I also recommend Eroll at EFI Dynamics.

Failing that, there's plenty of sponsors over at Australian LS1 and Holden Forums - take your pic on a shop, or post on that forum and you will get much LS1 help.

Cheers
Ben

[gjkrv8]

Thnks guys for the tips.

Ads.. I checked the Maf and it looked clean. Haven't checked the Map though. Might wait for an expert to look at it..

Ben.. What you say maybe true I will try. Essentially I drove it back from Rye last Sunday and last night I mucked around with the brake switches and had the power isolated. This morning I hopped in and drove it sedately down here and found it doing what it is doing.

Anyway I am sure once I get it to someone with a decent diagnostic tool they will figure it out. My odbii tool is very basic.

Its like what happens if you try to fang it when the engine is cold. I know you shouldnt fang it then but once it did. Anyway will keep plugging away

Thanks for the tips.. Reds Gregg

P.s. ordered a set of Ku36 front and rear on Friday for Shelby Fest. Just hope the engine hasn't stuffed up now - Murphy's Law. :-)

[paul68]

Maybe the cobra is telling you that it is time to upgrade to a ford coyote engine HA HA

[Gav]

I seriously doubt it is a PCM 'learning' issue, it should not be so noticable, you would have experienced it before if it was the case.
Bad or old fuel? If it is knocking it will pull timing out dropping power.
Or a blocked filter dropping pressure under load.
The plugs should last 100,000 k's so I'd not think that would be it either, but they may e grotty?

As Dave said about the only thing you should experience after powering down the PCM would be a wobbly idle. Powering it down again like you did would be the first thing I'd have tried, other than that you probably need someone to have a good look.

[Philm]

Have you checked compression?

[ICETOO]

...and if it knocking check both the knock sensor has not shifted and have a squiz at the crank angle sensor too.

As the guys have said there is a swag of fault finding intel on LS 1 forums...you do not have to be a member but simply agree to their T & C to view relevant posts.

One would hope it not a simple as old fuel with degraded octane or water contamination...a fuel sample and test will answer this possibility though.

[Rob. Smith]

MMMMM..Computer controlled veehicles ! I have a daily driver with a drive by wire throttle. I suppose that if it goes wrong I'd just coast to a stop. I have heard that there are common cars out there now that have drive by wire steering and brakes ! Technology is wonderful but this stuff is scary. I'm an old fart and like to "connect" the dots when it comes to steering , brakes and throttle. I'm slowly adjusting because my Cobras throttle IS connected by a wire...a metal one...not an electric one. ha ha ha. Solar Flares affect electronics too.

[Philm]

Try starting your car and take off once you have suffient speed turn the key off, wait 3 seconds, turn ignition back on then clutch start your car.

Take it for a drive and see how it goes.

If this solves the problem give your battery a good charge, as when starting the voltage can drop to low and the ecu will go into limp mode.

You also may not have reconnected the battery properly creating a bad connection and when under load... Starting.... You get a huge loss.

Just a thought.

Phil

[ICETOO]

WOW...the stuff you know Philm ...I had not even thought of that....definately worth a go!

[Philm]

Its stuff you learn the hard way.

Similar problem with an ls2 transplant in a VL Commodore.

Phil

[ICETOO]

Do the LS 1 powered cobras with the ECU set up have a check engine light or engine fault indicator lamp that that should come up when the ECU shifts to limp mode, (like the little check engine icon on the LCD screen in the VY cars).

If so you would hope the cars monitoring system could you there is a problem.

If not, its back to the plug and play with the OBD II from the network coms bus, and then old fashion hands on fault finding. Technology is unreal when it works but is a nuisance when it does not.

[Gav]

Not unless you have used the BCM as well.