Bad ground strap pooch perma tune box ?

[daburg]

I tried to start my 78SC after 6 months of hibernation and it would not start. I now know for sure I have a bad ground strap. I read a blurb on how this could damage the perma tune box. Is there a simple way to test this? Could the box be damaged and still send a weak spark?


livin n learnen
daburg

[Early_S_Man]

Bad or intermittent grounds can cause the Bosch or Perma-Tune units to have a weak output, or intermittent output that is OK on some firing pulses and non-existant on others ... simulating a misfiring fouled spark plug.

If the Perma-Tune unit is damaged ... it would most likely be permanently dead, and not intermittent.

There are braided groung/shield cables between the distributor and CDI-unit, and between the CdI-unit and coil, so is it one of those you say is bad, or is it the body-to-transaxle mount strap you found bad?

Instead of depending on the Perma-Tune/CDI-unit box to M6 bolt to the relay panel, and relay panel to body ground connection ... I like to run a ground strap from the CDI-unit to body directly.

[pwd72s]

Warren? Could you clarify something? RoninLB is sitting beside me as I type. He'd like to know if your "ground strap directly to body" means from the unit itself, or do you mean a ground connection from the male ground pin on the permatune unit to the body?

[daburg]

The ground fault that I know for sure is from the transaxel to the body. I know this because when tring to start, the engine was slow turning over. First I thought it was the battery, and it was. I tried boosting it and had only slight improvement. I then ran a booster cable from the battery negative to the air pump bracket and that made a big difference but still no start.

daburg

[Targa77]

Try http://www.permatune.com/Technical%20Support/Porsche/911.htm It ex[lains how to perform ground tests.

[Early_S_Man]

ALL ground straps should be inspected and cleaned ANUALLY!

Paul & Ron ... what I do is put a strap (similar to the one grounding the engine lid for EMI/RFI shielding) with a precise 1/4" - 6 mm hole, and approx. 1/2" width directly under the forward lower mounting hole of the Bosch/PermaTune unit after sanding with 320 grit wet-or-dry ... down to shiny, bare metal, and spreading a bit of anti-sieze compound where the ground strap will be clamped) ... so it will be clamped between CDI-unit and the relay panel. The other end of the strap goes next to the body panel after cleaning with a Scotchbrite pad and applying anti-sieze compoud ... under the spacer for the forward relay panel mounting bolt. A good ground strap also eliminates potential Voltage regulator problems with grounding!

The PermaTune site grounding test procedure is a bit lame! Considering the size of the OEM Porsche grounds straps, I want all readings to be 0.1 Ohms or LESS, and most of the digital multimeters on the market aren't capable of readings that low with any accuracy! Four-wire resistance measurements with Kelvin clips would be desirable, too, but beyond the capability of most Porsche DIY mechanics (and most "pro's" too) that won't have a precision, 4-wire bench DMM like a Fluke 8800A or good analog MilliOhmmeter like an HP 4328A! Resistance measurements made by the 4-wire metrhod eliminate errors caused by the 2-wire method wherein the test leads carry the constant current used for the measurement through the unknown resistance, and also carry the Voltage drop accross the unknown to the Voltmeter circuit! In the 4-wire method one pair of test leads carries the constant current, and a second pair of test leads carries the Voltage drop signal back to the measurement circuit.

[pwd72s]

Warren...thanks for a great answer..I'm on Paul's machine...what happened is that on this Big Ride and I'm on the Extraterrestrial Highway in Nevada..I'm doing about 3.4 or 3.5K and my engine does a quick instant on/off..I look up thru the roof and don't see anything..I then start thinking, either fuel or ignition?? No problem for another 400 miles..then same on/off again..another 200 and on/off then full death a short time later..5 minutes to restart..same routine for another 1,000 miles..I order a new Permatune and get a new coil from NAPA..anyway, I run a 12 ga. wire from the male pin on the Permatune to back up the other male pin to harness ground...Right/wrong it doesn't matter, no time for problems on the other side of the world..NO problems in 2,000 miles.. Original Permatune which Paul is sending, w/coil, to Permatune for factory testing. I want to know what they say... ALSO Warren, I did an overkill chassis ground to starter case w/ground strap and earlier I posted the set up w/pic.....RoninLB

[Early_S_Man]

Ron,

So ... now we know the rest of the story behind the emergency PP delivery to Paul's house in his 'Great service' thread! Actually, your 12 ga. ground wire from the Faston connector is perfectly good, assuming that there isn't any corrosion under the screw head which connects to a ground lug on the other side of the anodized aluminum panel.

With older Bosch or PermaTune units ... annual cleaning of that ground double Faston connector and its' fastening screw should be done to preclude any mysterious problems from corrosion buildup.

I tend to think that PermaTune has Alfred E. Newman writing some of the technical BS on their website! I bet you just loved their statement that 'the PermaTune unit always fails safe!' RIGHT! And in a previous NASA job, the guy probably wrote the faulty specifications for the LOx tank for Apollo 13 Service Module! I bet PermaTune says "No trouble found!" on your flakey unit.

[pwd72s]

Warren? Paul this time. Ron is headed out, presumably for parts of the USA with less rain than here. (As an aside, the lawn fertilizer I just spread is getting wonderfully watered in tonight, courtesy of momma nature.) All that aside? Believe me...Ronnie's 12 gauge ground wire IS grounded. Connections to the wire soldered...the 12 gauge ground wire is marine grade, "tinned"...and the ground connection has been tested with a Fluke brand mutitester. Other than you? Ron is a guy as much concerned about 911 wiring as anybody I've known! Thanks for your response! Best, Paul

[widebody911]

The PermaTunes are crap, with a useful life of 12-18 months.

BTDT (been there, debugged that)