Limp Home Mode

[dougie]

I had some problems with my 86 GN dying out, not idling and got some weird codes. I then disconnected to orange wire by battery, and cleaned and snugged up the ecm connectors. Car started and seemed to run fine. But now that I drove it a little, it is running rich, and hesitiates off idle. No SES light and no codes.

I put scan tool on and am getting the message: " Back up fuel and spark active" and "ECM is in "limp home mode". I disconnected battery, re-connected and got the same message. Started and ran a little, same message. Still no codes. It has larger than stock injectors (32# I believe). I am going to check my ground as I've been out of town and haven't done that yet.

Any ideas? Thanks guys (and gals, need to be politically correct)

 

[Lee_Burough]

I drove a TTA 100 miles home with similar symptoms after disconnecting the MAF....

Look here for some ideas about where to start on which systems. Enter the list with your error codes and follow the suggestions as you see fit.

 

[dougie]

I'm not getting any codes, and the SES light did not come on. Prior to this I had a bunch of codes and thought it was a bad ECM. I was getting wrong TPS voltage, -40 degrees AIT and -40 degrees coolant temp among others. Plus the car wouldn't idle. Checking the connections cleared all the codes and fixed the start up and idle, but now it's running in limp home mode. I just checked the ground to engine and it is good. Bad ECM? Any way to test it?
Thanks all.

 

[SFITurbo]

Clean the connectors at the ECM and reset the chips. Mine threw a code that doesn't even exist due to a loose connection.(and did exactly what you described).

 

[dougie]

I already cleaned the harness connectors to the ECM, but didn't remove the chips to clean. I'll try that tomorrow. Gotta be something like that. Thanks.

 

[garyk1970]

as posted in the first reply,replace maf with a known good one,they will go bad and not have any codes,i know by personal experience.

 

[GNVenom]

First make sure the SES light is even functioning. Key on, it should blink once.
Next, use the paper clip routine to flash out the codes...12 12 12 then the real codes.

Since your scan tool suggests limp mode, the SES light should blink rapidly or stay on during run time. Otherwise, a poorly calibrated MAF sensor will cause undesirable operation, as will a sluggish O2 sensor. A disconnected MAF sensor will cause a "default" condition, not a limp mode condition.

Disconnect the MAF and look for the SES light to turn on.

 

[dougie]

Who makes the best chip for street?

Well, I pulled the chips to clean connections, and I have a "Pit Bull" chip. Looked online and comments are it's old, a piece of crap with lots of timing, and too much for pump gas. I'm new to this GN thing, and I know I need a new chip. I just installed a 3" downpipe, has intake and I'm told 32# injectors. That's about it. I've had the car about 3 months, so I'm still discovering things. Car has 30K miles and hasn't been driven a lot, so old chip in there makes sense.

Any chip recommendations? This car will be used 99% on the street. Thanks.

 

[jretrodude]

turbotweak chip or red armstrong 93 I've got a red and runs awesome

 

[SVORay]

TurboTweak chips seems to have a lot of raves. I ordered a street chip from Eric ( Turbotweak) but I haven't gotten it yet. The chip is adjustable as well...atleast on the race chips. My chip was a Turbotweak race chip and I ereased the settings cleaning a battery cable. It was cool since I now know I had the wrong chip for what I'm setting the car up for. The car ran really strong before I unpluged the battery.

 

[dougie]

The SES light flashes on and off once when I turn the ignition on, then stays on until the car is started. Then the SES goes off. This is the correct operation, right? With the car running, I disconnected the MAF harness and SES light came on. Scan tool shows code 34 for MAF malfunction.

With the car running and later off, scan tool still always shows ECM in Limp Home Mode.

I've checked all connections and grounds. It starts and runs, but is apparently in Limp Home Mode. I read in another post that when in limp home it defaults to stock settings, meaning 28# injectors. I have 32# from the numbers on the injectors. Wouldn't this cause it to run rich because it's pulsing at a 28# setting? When you drive it, it hesitates on acceleration. And it smell rich.

Also, scan tool reads "A/F Learned: No" Is this an indicator of the limp home mode?

Could the chip cause this? Or is it maybe time for a new ECM? I don't like to waste money but a reman ECM is only 80 bucks at gmpartsdirect.com. Think this is a good idea? Any and all comments and suggestions welcome. Thanks.

 

[mikestertwo]

As posted above, MAF sensor. Put a known good MAF on.

 

[dougie]

Anyone in the Chicago area (NW suburbs) have a good Maf that I could try?

What I still don't understand is why I'm getting the "limp home mode" on the scan tool, What does this really mean?

Thanks.

 

[Lee_Burough]

Anyone in the Chicago area (NW suburbs) have a good Maf that I could try?

What I still don't understand is why I'm getting the "limp home mode" on the scan tool, What does this really mean?

Thanks.

Sorry, without an actual error code number, I wouldn't know where to start....

 

[mikestertwo]

Limp home means data from a sensor or prom is invalid so the computer uses a default setting to keep you running.

 

[GNVenom]

Your scantool is wrong. You're not in limp mode. If you were, the SES light would tell you so. You're probably out of some parameter window, most likely the MAF sensor, and second-most-likely, the O2 sensor.

Start with a known good chip. But, you need to KNOW what injectors you have, and a "probably" won't cut it for the chip burner...injector flow is essential for chip programming. Look for identifying features on the injectors and check on-line for info.

John

 

[dougie]

Thanks John. The O2 sensor is a new Delco. Has maybe 10 miles on it. I checked the injectors and they are green stripe # 5207009, which I checked on line and are shown to be Lucas 33.2 lb. Injectors.

The car ran fine with this setup until the recent incident where it stopped running while driving and wouldn't restart. At that time, it threw all kinds of codes. After cleaning ECM connectors (which didn't show any corrosion) it started OK, but has hesitation when accelerating. Also smells rich, but no codes. Car has an old Pit Bull chip which is going to be replaced. I'm getting info using my buddies Snap On scan tool. That is where I got the reading that shows Limp Home Mode.

The only things I did after the dying out incident was new plug wires (AC Delco), new O2 sensor (AC Delco) and cleaning the ECM connectors.

This is my son's project car. He is thinking of 42lb. injectors, LT1 or LS1 Maf and translator, and new chip. Just put on the 3" downpipe. In this situation, would you try to get it running right, before making these changes, or make the changes now. It's not going anywhere anyway with winter coming in Chicago. Again, we're both new to these cars, so all help is truly appreciated.

Thanks.