Cupcar#12

Basically -

When i hit a bump the ignition cuts off for 1-2 rotations (normally very quick) and restarts - so definitly spark/ignition related. no other electrical systems are effected (stereo, lights) that i can tell in the time the cut off happens

this happens with the engine hot/cold, etc... When hitting road dots (the small US ones) pavement seams, etcs seems most pronounced when going over bad pavement that has regular seams (long frequency bumps?) - this happens with either of my DME's as well (RS + stock C2 replacement)

I have done the following
Replaced the battery (optima red top with Internstate for C2)
Replaced the positive cable,
Replaced the DME relay,
Reconnected and tightened the DME (also disassembled and checked the chip to make sure it was tight),
Checked and tightened all grounds in the trunk (Battery + the 2 in the trunk) the Grnd in the Central electrics box, under both seats (DME and ACU) and the 2 in the engine compaftment, All Grounds are clean and showing no signs of corrosion (or anything for that matter)
All relays have been reseated and checked in the Central Eletrics and engine relay/fuse panel).
I also pulled and reseated the plug for the DME relay in cetral electrics.
I reseated the connectors on the ACU as well

i am about to disaaemble the lower dash to get at the ignition switch and check and insulate as needed. Plus i am going to check the fuel pump and see if there are any loose connections there.

i thought i fixed it when the battery kept coming loose (optima and an interstate normal C2 battery) but the symptoms are the same regarldess of the battery.


Do you have any other idea's, i'm about to give up and take it to the shop but what the heck i've come this far so might as well try *Everything*

* also the car is US Carrera Cup with the race suspension and 18" wheels - basically very, very stiff. My normal drive to work is very smooth so i am not sure how long this may have been happening but has to have started in the last 3 months.***

gfunk

If it's repeatable I would rent/get hold of a digital storage scope and start monitoring various signals when traveling over the bumps. It likely wouldn't be too difficult to track down a signal that was misbehaving. I would start with monitoring the 12V going to the distributor coils, fuel pump, dme etc.

Greg

Cupcar#12

ok - what is a Digital Storage Scope? and how would i go about doing that?

a Hammer yes pretty easy to get hold of,

gfunk

Something like this: http://www.trs-rentelco.com/Model/TEK_TDS2014B.aspx or find a buddy in the high tech business with access to one.

Cupcar#12

ok, thanks
not sure if i can impliment that one without a lot of time since it is not easily repro-able

any other suggestions would be helpful as well.

PCar SBA

Reading and re-reading your first post it seems you have an issue where the engine cuts out. And you jump to the conclusion it is ignition-related. Not so fast. Been there, done that.

Mine is a 3.6 conversion into an earlier car I did myself. I ran like clockwork for several years. One day I felt a short ever so slight hesitation. Strange I thought but didn't give it more thoughts at the time. Several weeks later cruising the HW the engine all of a sudden cut out like someone turned the key off for several seconds. And then it would catch just like nothing happened just before I was ready to coast over and call AAA.

I was 100% convinced that my spark cut out. No sputter but a complete "nothing" for seconds at a time. Put in the spare DME relay and no improvement. This happened maybe once a week and I thought bumps made it appear. But nothing I could put my hands on.

I Hooked up my Hammer and kept is on every time from that day on. When the gremlin showed up the next time it turned out to be the O2 sensor signal. The signal went from its ususal swing between 0.1V to 0.9v to 0.00V. Turned out to be a poor contact at the connector in the engine bay. And believe me the engine literally felt like someone cut power to the coils or turned the key off. After cleaning the contacts at the 3-pin plug it never happened again.

If you can get a Hammer try and monitor that signal - could be your issue.

Ingo

aeroman

Rob - If you want to borrow my scantool to monitor you are welcome to it.

Cupcar#12

Thanks Aero man - but i can get a hammer to monitor the engine signals - easier to get the full spectum

good call on the O2 sensor - i'll double check the connectors on mine and switch out to a spare if it seems to be hooked up fine in advance of getting the hammer

Update..
i removed and checked the fuel pump last night - no issues no corrosion, etc.
reseated the DME chip and checked the boards for cold sodder breaks
i also removed and checked and reated the Central eletrics main panel and the DME plug.

i drove my test road before reseating the chip and Central Eletrics board and connectors & only repeated the cut off once when hitting a manhole cover - my normal test road did not replicate the condition.

i will give it another day or two before futher digging (other than the O2 sensor)

ltc

I'm guessing you've already replaced the DME relay (with the newest 993 P/N variant)?

gchristofi

Another couple of quick checks to make
1. Make sure your hall sensor connector has not come loose from the distributor housing...
2. Check the connection to your Air Flow Meter... there was a tsb for an update on this, search here an you will find the link..

I had similar issue to yours and not really sure what cleared it. Hasn't come back for about 1000 miles of driving but the above to are prime suspects... Good luck

Cupcar#12

Check - DME relay replaced (again last night)
Hall senor - checked no frays or loose connections
AFM - checked and TSB preformed Plus oil return pipe bracket bent twords front of car - the return tubes do not touch the AFM sensor connector. Connector has been modified to tie wrap the leads to the side.


keep them coming

ltc

No indication on the dash gauges (i.e. tach) when this happens?
Fuel pump wiring/connections?

Cupcar#12

normally there is a brief CEL that immeditaly goes away.

I did discover a small exhaust leak between my fabspeed cat delete and the stock primary muffler. Maybe?

Cupcar#12

leak fixed & checked the O2 leads as well, connected and fine. We'll see if it does it again

tall02

I had the same problem. Engine would cut-off on small and large bumps about 1 or 2 times on a 20 min ride. Lights would not dim or flicker. Thus I traced the electrical circuit to the ignition switch. Replaced it and Bingo.

Good luck

Tall02