Got the ride of shame last night, crazy fueling problem

[1986911]

Got the ride of shame on the way to a car show last night.



Clicked off about 30 miles of freeway driving, so far so good. Hit a traffic jam and car started to get warm. The needle got to 9 o clock or half way between the two white hash marks. Hot but nothing out of this world. All of a sudden car lost power, afr's went to 19.5. I pulled over, changed the fuel pump relays and put in a new fuse. Fired up, same 19.5 afr's, I limped to the next exit. I found a walmart and after doing a quick under hood and bonnet check (about 5 min). I fired her up and it was back to normal?

Got towed back home just in case.

Today cranked up the car and warmed it up. Right on cue at the same temp the gremlin was back. I pulled the FP relays (one at a time) and idle stayed right at 19.5 regardless of which one was on. I pulled the rear round relay next to the yellow relay and the same. ( the car did react to pulling each relay but did not shut off).

I did notice when I pull the rear fp relay, and put it right back in, it clicks and my idle richens up for a few seconds and then goes back to lean. Same goes for the round one next to the yellow relay in the back??

My CDI box was very hot but the car was idling with the hood closed so it was pretty warm in there.

I changed that black round relay in the back to a new red fuel pump one I had about a month ago. Nothing else after that. I changed it because it seemed old and original. I have driven about 150 miles since then and had no issues.

Any difference between the red and black round relays??

I shut off the car with the gremlin active and pulled the green plug out. I opened the ignition, the frequency valve was buzzing and pumps sounded normal.

Prior to the initial firing up today, I did the normal check of pins and corrosion. I took my seat out, sanded and cleaned all the pins down there and coated them with some dielectric grease. Same goes for FP relays, they are a few months old anyway.

My rear fuel pump is also few months old. I had the same symptoms but the lean idle was constant.

My problem seems specifially tied to hot engine temps.

I spent a few hours reading past posts but I am stumped!

[mark houghton]

Sounds like you've covered almost everything. A few possibilities: First, I presume there are no other outward signs of running lean - other than the gauge reading 19.5. Could be the WUR is acting up (put the test gauge on, run the car until the problem shows up again and check the warm control pressure), could be your AFR setup is acting up and giving false readings (try calibrating it?), could be a voltage regulator issue (I say that because my voltage regulator is becoming problematic when the engine is hot, causing high voltage overcharging while at the same time causing my Innovate AFR to suddenly read low - the reverse of what you're seeing), could be your Lambda system is acting up (frequency valve not operating would cause a very lean condition).

[smurfbus]

Did it run on 6 cylinders or did it sound different? Misfires show as lean on widebands so maybe your ignition system malfunctions when it gets hot?

[1986911]

Originally Posted by mark houghton

Sounds like you've covered almost everything. A few possibilities: First, I presume there are no other outward signs of running lean - other than the gauge reading 19.5. Could be the WUR is acting up (put the test gauge on, run the car until the problem shows up again and check the warm control pressure), could be your AFR setup is acting up and giving false readings (try calibrating it?), could be a voltage regulator issue (I say that because my voltage regulator is becoming problematic when the engine is hot, causing high voltage overcharging while at the same time causing my Innovate AFR to suddenly read low - the reverse of what you're seeing), could be your Lambda system is acting up (frequency valve not operating would cause a very lean condition).

Thanks for the reply Mark, as soon as the car starts acting up I lose all power. I could barely keep the car at 20mph in second trying to get off the freeway. Car idles very rough and at low rpms maybe 500? Same exact symptoms as when my
rear fuel pump failed. I was blowing fuses and the pump seemed basically locked up. I would pull the front pump relay out and car would die right away. 2 new FP relays, new fuses and new rear pump. Less than 500 miles happy miles on new parts.

Good idea on checking the voltage, I am going to try that tomorrow and swap in a known good black round relay in the back. I also plan to pull the green plug and shut the motor off to see if the bee hive is alive! Hopefully one of those will give me a clue.

[1986911]

Originally Posted by smurfbus

Did it run on 6 cylinders or did it sound different? Misfires show as lean on widebands so maybe your ignition system malfunctions when it gets hot?

Not sure how to tell if all 6 cylinders were firing, idle was weak and pretty rough. No clue on checking ignition. I am still getting the hang of fuel pressures!

I am going to do some searches on checking ignition, thanks for the tip!

[mark houghton]

Originally Posted by 1986911

Thanks for the reply Mark, as soon as the car starts acting up I lose all power. I could barely keep the car at 20mph in second trying to get off the freeway. Car idles very rough and at low rpms maybe 500? Same exact symptoms as when my
rear fuel pump failed. I was blowing fuses and the pump seemed basically locked up. I would pull the front pump relay out and car would die right away. 2 new FP relays, new fuses and new rear pump. Less than 500 miles happy miles on new parts.

Good idea on checking the voltage, I am going to try that tomorrow and swap in a known good black round relay in the back. I also plan to pull the green plug and shut the motor off to see if the bee hive is alive! Hopefully one of those will give me a clue.

These cars will run pretty well with just one fuel pump, until you start challenging the delivery under substantial load. Note that the rear relay you refer to controls the power to the Lambda stuff and has nothing to do with your pumps (those two are up front). So when you unplug/plug back in, it will weird out your lambda controls for a spell, as you've already seen. Sounds to me as though that is working ok.

Since you're experiencing symptoms beyond just AFR meter readings, something is amiss. Your hot CDI might could be the culprit because with a poor spark you'll see high AFR readings (because the combustion isn't complete, thus the oxygen hasn't all been consumed, and your AFR gauge reads residual O2 in the exhaust).

[Tt surgeon]

I had the exact same thing.
Last summer I drove to work in the city, no issues. Driving home I got caught in 90 degree bumper to bumper traffic. Started stumbling, backfiring, died. Ended up being the coil and cdi fried, and at least one burned out fp. I've been gun shy about those road trips ever since.

[1986911]

I hit the cdi box with my infrared thermometer yesterday as I was checking relay and fuse temps. It was 147 degrees. Not sure if it was picking up heat from the engine but very hot.

Any way to test cdi box?

I spoke to my detailer and he mentioned he gave the engine compartment a once over with some light degreaser and low pressure water? This was Saturday morning. I figure if something was wet it would have dried on that 30 mile drive before the ride of shame?

[1986911]

Originally Posted by Tt surgeon

I had the exact same thing.
Last summer I drove to work in the city, no issues. Driving home I got caught in 90 degree bumper to bumper traffic. Started stumbling, backfiring, died. Ended up being the coil and cdi fried, and at least one burned out fp. I've been gun shy about those road trips ever since.

Crap, would it go away after the car cooled down? My car seems runs perfect after just a 10 minute cool down. Once it heats up again, the problem is back.

[Tt surgeon]

Yes, cooled down, went another two exits and died like a dog. Flatbed home, hearing it from the wife, glorious day!
CDI, no spark, runs rich, backfires like a howitzer.

[mark houghton]

Originally Posted by Tt surgeon

Yes, cooled down, went another two exits and died like a dog. Flatbed home, hearing it from the wife, glorious day!
CDI, no spark, runs rich, backfires like a howitzer.

And that's the confusing part for some...runs rich because of unburned fuel, but the AFR says it's running lean 'cause of un-consumed O2. Either way, runs like crap!

[Ronnie's.930]

Originally Posted by 1986911

I hit the cdi box with my infrared thermometer yesterday as I was checking relay and fuse temps. It was 147 degrees. Not sure if it was picking up heat from the engine but very hot.

Any way to test cdi box?

I spoke to my detailer and he mentioned he gave the engine compartment a once over with some light degreaser and low pressure water? This was Saturday morning. I figure if something was wet it would have dried on that 30 mile drive before the ride of shame?

Water beneath the distributor cap would not dry out in 30 minutes (many threads about this in the 911 forum). This can cause a misfire/rough running, but might not be the case for you given you say it runs fine when cool . . .

[Tt surgeon]

I think if you're getting no spark, no combustion, then the AFR would be all over the place.

[1986911]

It looks like its my CDI box. Check out photos below, look at the broken link\ melted link in the yellow box. Its the 31/1 circuit or system ground according to my searches. If anyone can post a picture or can confirm that my link is broken and theirs intact. I want to make sure it broke and not supposed to be like this before reconnecting link.

OSI930 Thanks for the offer, you are great. You also have a pm!

That 31/1 wire goes to the negative post on the coil. Could my coil be going bad and caused this to melt? I just don't want to get a new box and have the same thing happen again.

Both my CDI box and coil are original to the car, I am almost positive its the cdi. I doubt Bosch would have that link like that.

Is it common practice to get a new coil when getting a new cdi box?

Thanks!

[mooney265]

I've noticed these guys for the "rebuild" or "check-out"...

Porsche 911SC CD Box, 6 Pin Bosch 0227300004, 0 227 300 004 - Specialized ECU Repair

[1986911]

Originally Posted by mooney265

I've noticed these guys for the "rebuild" or "check-out"...

Porsche 911SC CD Box, 6 Pin Bosch 0227300004, 0 227 300 004 - Specialized ECU Repair

Just ordered one from them off ebay. I like the 5yr warranty. They also bead blast them, clear coat them and put factory reproduction stickers on them. Pretty good deal for the price. Another factor is they charge a big core but send the box out first. In other words, the car is back on the road in only a few days vs sending in core to be fixed.

I think I will bite the bullet and also get a new coil.

[Tt surgeon]

Yes, always do a coil w the cdi box.

[1986911]

Originally Posted by Tt surgeon

Yes, always do a coil w the cdi box.

What coil did you go with? The one in the car has a 0 221 121 001 part number on it. But my parts book and this pelican has another part number listed?

[1986911]

Update, new cdi box and problem is gone. The 31/1 wire goes to ground on one of the two studs that coil attaches to. I mistakenly said it went to the negative post on the coil. I checked all my ground resistance and all was good. According to the ECU Dr's that melting of the 31/1 link is pretty common, I was concerned a poor ground caused the link to melt.

[JFairman]

Saying you always replace the coil with the CD box is totally ridiculous.
There is not one single reason to replace it if it is not leaking oil and working well.

Also if you have an old black painted steel casing bosch coil that says made in Germany on it you can not buy a better coil for the bosch CDI anymore because they havn't been made in Germany for a long time now.
Bosch coils are made in Brazil these days and you never own them you only rent them. Anotherwords they don't last long. Just a cheap third world whore of a coil.

If you have a German made bosch coil keep it or sell it for alot of money because they are now collector items. Porsche restoration folks will buy them because they are no longer available.

The highest quality coil you can now buy new that has the correct impedence for a bosch or permatune CDI is the epoxy filled permatune coil that will never leak out oil because there's none in it. It's black too so at quick glance it sorta looks right.

The POS brazilian bosch coil is clear anodized aluminum and if you have to use one of those mount it right side up instead of upside down because that way the oil will probably stay in it through all the heat cycles and vibration it goes through mounted on the fan housing.

In the end... it's best to switch to MSD CDI and MSD high vibration epoxy filled "blaster" coil. That coil is also black under the teenage meathead sticker on it.