Troubleshooting Challenge...car wouldn't start at the track

[87LtdT]

So the car has sat pretty much for 1.5 years...heated garage. Got it all spruced up and ready for the track and headed off to Indy. Car started and ran trouble free for 60 miles. Got to the track and decided to do my first run at 100% street setup and boost limited to 17.5. As a precaution I dumped in 5 gallons of pure C16 that was 1.5 years old. Gas left in the tank was about 3 gallons of a mix of brand new and 1.5 years old.

Start the car and head to staging lanes. Get in line and shut off. Restart to move ahead a couple times. Somewhere in there the check trouble light came on...thought it may be the C16 killing the Oxygen sensor...car still ran OK. Then the car died. Restarted...died. Restarted...died. I got to within 4 cars of the starting line and it would NOT restart. Pushed it backwards out of line...not the way the mighty Buick should travel!!

Car would start but die....sort of the way it does when anti-theft device is engaged. Overroad the anti-theft device repeatedly to be sure it wasn't my problem. Suspecting that the 1.5 year old C16 was the problem I drained it all and replaced with 5 gallons of brand new C16 I bought at that moment from the track. Didn't make any difference. Eventually hooked up the hose to the fuel rail drain to see if I had good gas supply. And here is the very interesting part.

With the hose connected to the fuel rail the pump pushed fuel into the tank for 2 seconds on initial key on...just like it's supposed to. Then I turned the key a bit more to start and it started immediately and continued to run and accelerate with a steady stream of fuel coming from the fuel rail hose into the gas can. Thinking we had "solved" the problem....even though we didn't know what the problem was...we removed the hose and reinstalled the fuel rail cap. Wouldn't start. Put the hose back on and it started. Cap back on the fuel rail and again no start. Reduced fuel pressure at the regulator to about 30 psi and it sort of seemed to start and run just a little but basically there was no change...wouldn't start. FP had been at 45 (line on) like it has been for 5 years or more. So reinstalled the hose for the 3rd time and it started immediately and ran fine. While running I kinked the fuel drain hose near the gas can and car died immediately!!! Replaced the cap, and put tools away.

Gave up at this point and arranged for a tow back home after end of racing. Friend and I left the car in place and watched the racing for 30-45 minutes. Went back to the car and it started perfectly. Shut off and restarted. No "check engine light". Told the "guy" we weren't gonna need a tow and headed home. Stopped nearby to drain the brand new C16 and partially filled tank with 93 octane. Drove 60 miles home with no problems. Driving thru hometown at 35 MPH, steady speed, no throttle changes, no radio station changing, nothing at all going on and the car died. Coasted to a parking lot...where I tried to restart. Would not restart. Reset anti-theft device and it started immediately. Drove another 15 miles to drop off friend and go home with no problems.

So WTF is that all about??

Anti-theft is a feature in the ECM....have had it for 10 plus years with no problems.

Thanks for any insight, Bob

 

[pacecarta]

pull the malfunction code from from the check engine light

sounds like ign module

and what gauge are you using to determine fuel pressure

 

[RmvBfrFlght]

Most likely the ECM was in limp mode. With the larger injectors this will make it run very rich. By lowering the fuel pressure (hose on fuel rail), the injector flow was closer to the limp mode calibration (little chip in ECM contains the limp mode calibration).

When in limp mode the ECM isn't running the real firmware (the chip), it is running off the redundant fuel device which is calibrated by the CALPAK (a bunch of resistors).

A quick check to see if the ECM is running from the chip is to:

Key-on, engine-off and observe the SES/CEL light. It should, turn on briefly, blink off, then turn on solid. Can repeat the test after a minimum of 10 seconds of key-off.

If the SES/CEL (which is it on our cars??), just turns on solid, or not at all, then the ECM isn't running from the chip.

RemoveBeforeFlight

 

[TurboBob]

with the 7148 ecm, the SES light generally flickers when running on backup fuel.

if the antitheft was resetting, then look for voltage dropouts.

If the battery is low, starting can cause issues with the antitheft because the voltage dip from the starter engaging resets the ECM.

Another thought is the fuel pump or wiring. There is a junction in the stock harness under the rear seat (I think) that caused a similar issue with a friends car a few years ago.

Bob

 

[RmvBfrFlght]

with the 7148 ecm, the SES light generally flickers when running on backup fuel.
Bob

That would be a checksum error of the chip (PROM). So that is another possibility for limp mode: no blink off and either: solid on, not on, or flickering (steady flashing).

I haven't used a '7148 for so long I forget about stuff like it having on-board ROM.

There is an opportunity here for Eric, provide a re-calibrated CALPAK to go with his chips.

RemoveBeforeFlight

 

[TurboBob]

After re-reading the original post, it may be time for a new fuel pump.

Bob

 

[87LtdT]

I might add that when we left I pulled a couple of WOT (17 psi) 15-60 mph runs and it ran absolutley great...would it do that in "limp" home mode??

I can't work on it till later this evening but will report what I've found.

As always I appreciate your advice.

Thanks, Bob

 

[RmvBfrFlght]

I might add that when we left I pulled a couple of WOT (17 psi) 15-60 mph runs and it ran absolutley great...would it do that in "limp" home mode??

I can't work on it till later this evening but will report what I've found.

As always I appreciate your advice.

Thanks, Bob

> mph runs and it ran absolutley great...would it do that in "limp" home mode??

Not likely, but at this time the ECM was running OK, not in limp mode. Which is why it started and ran with the fuel system buttoned up.

RemoveBeforeFlight

 

[87LtdT]

The malfunction Code is 51.

When keying on the SES light comes on, flickers once, and then stays on.

After starting, the engine the SES light is not on.

Any chance this is related to having a PC plugged into the ECM using PowerLogger. I haven't touched the ECM for years!!

Bob

 

[87LtdT]

The malfunction Code is 51.

When keying on the SES light comes on, flickers once, and then stays on.

After starting, the engine the SES light is not on.

Any chance this is related to having a PC plugged into the ECM using PowerLogger. I haven't touched the ECM for years!!

So why after an hour or so did "reset" itself out of limp home mode??

Fuel pressre read from gauge attached at the end of the fuel rail.

Bob

 

[imjoesnuffy]

I was having a very sporadic Code 51. It would go weeks without it happening and then 5 times in one day. I would pull the ecm cable at the battery then check the chips in the ecm and the powerlogger, it would restart with no code 51, then do it again sporadically throughout the day. I tried a different ECM, a different TT chip nothing seemed to solve the problem

Here is what I did to fix it:

In the instruction for modifying the ECM case for the powerlogger, it says to put electrical tape around all of the edges that were cut off to prevent damage. I wrapped electrical tape around the ecm a few times at the bottom edge where the powerlogger connects. I then took several strips of electrical tape and wrapped it from one side of the case to the other over the powerlogger, then a couple more strips around the ecm case. This insures the powerlogger cant wiggle loose from the ECM. I havent had a code 51 since then. Hope that helps.

 

[TurboBob]

you could remove the PL for a little while and see if the symptom changes... If the PC is plugged into the cig lighter, and into the PL, and the cig lighter has a bad ground, the PC will try to charge using the ground wire in the USB cable. Not a good scenario. I try to always run off the PC batteries when plugged into the PL.

Bob

 

[87LtdT]

OK thanks to you all...

Bob, I was running the PC from the cig lighter and just before my issue I remember moving the related wiring around so that when I launched it wouldn't fly backwards...I may have caused a glitch by doing that. I will wrap the ECM per JoeSnuffy's pics (thanks a lot). RemoveBF4 your explanation of big injectors flooding the engine makes perfect sense now...it was acting as if it was flooded but we couldn't for the life of us figure out how an injected engine could be flooded....thanks for your accurate insight.

Now one more question...why did the engine die while cruising at 35mph after 50 miles of uneventful driving on the way home? Wouldn't initially restart...reset the anti-theft and it started immediately with no more glitches for the next 20 miles?? The PC was not plugged into the cig lighter or Powerlogger port on the trip home. Now would be an appropriate time to mention that the engine died twice enroute to the track...once after a little throttle to gently climb my friend dirveway where when reaching the flat top I let off gas and it died...the other time was when let off the gas to coast to a traffic light about 50 miles later. The PC was connected to cig lighter and powerlogger port on both of those occasions.

Bob