cold start enrich '71E

AZ911E · 09-08-2007, 09:34 AM

New forum user here...I'm seeking info on my 71E 2.2 (all original) cold start fuel enrich circuit. I know that an enrich pump engages with the starter motor circuit, and it used to work correctly, but now does not. The enrich pump works when I apply 12V, so it must be a relay somewhere. Where? The circuit diagrams I've seen are not very usefull in locating components.

This garage queen is driven only a few hundred miles a year (never in hot summer months), and always runs beautifully with that lovely snarl above 4K.

I'll be pulling her out of summer storage next month and will try to fix this defect. Cold starts have been made with use of starting fluid recently, and I can verify that it's a bad habit to have with one interesting inlet fire.

A little help for a forum newbie?

boxster03 · 09-08-2007, 01:04 PM

the solenoid for the cold start is found on top of the fuel filter - there is a single brown and white wire attached.

911s55 · 09-08-2007, 02:29 PM

Cold start, IN PHOENIX ?

304065 · 09-08-2007, 04:07 PM

WELCOME to the forum. Lots of us 71E guys here.

Best advice I can give you is to use the search function with the terms "cold start MFI" and in particular the users "Grady Clay" and "Early_S_Man." This is, as you might imagine, a fairly popular subject, and has been covered here extensively in about 30 threads-- once you familizarize yourself with the issues, wiring, solenoid, fuel flow, drippers in the stacks, interrupting the circuit with a push button on the dash, etc., then fire away with any questions you may have.

Good luck! I use starting fluid too, mine's been disabled until I can do it right.

AZ911E · 09-09-2007, 08:46 AM

thanks all, especially John. I'll do my research soon and get back to you. this forum is awesome for us do-it-yourselfers, and I'll eventually get to read everything.

It's possible to get her started without enrich, but rough on the starter.

Not sure if I got this thread started in the right location. Will try to do better next time. I'll be a regular user - have 63B also.

AZ911E · 12-03-2007, 04:43 PM

OK, I just resumed work on my 71E, and I just spent two hours reading the extreme detail contained in the "ultimate MFI resourse". Unbelievable - love this site all all you contributors. Problem is, you know the factory made significant enrich system changes from the 2.0, 2.2 and 2.4 models. I was running to the garage comparing my (stock) system to all the excellent suggestions and advise. None of the info seemed to "fit" - the enrich (bimetallic) timer is not (apparently) located at center of engine, and there are no electical connectors at the MFI pump. MFI thermostat is now cleaned, but probably not adjusted properly.

The root cause is NO ENRICH SQUIRT abover the stacks (metal stacks on the 2.2). I have chased the electical signal path, (example: metering the solenoid VDC while cranking the engine - uh, I can't always get my wife to run out to the garage when I need four hands). I can force the squirt by putting 12 VDC at the solenoid. Something is disabling the enrich squirt, and it could be the bimetallic timer - if I could only find it.

This engine runs very well across it's full range after a liteoff on starting fluid. It will start without enrich for a few hours after fully warmed-up shutdown. I drive this old girl only a few hundred miles each Phoenix winter season; a classic garage queen - I enjoyed her for the last 25 years, and regretfully am thinking of selling - fleet reduction.

So, I regret dredging up this old subject, so well covered in the 2002-2004 timeframe on this forum. but, this is getting anoying - the staring fluid habit, I mean. And I prefer to retain my wife.

71 911E
Thanks all......

304065 · 12-04-2007, 12:04 PM

Bad thermo-time switch is my guess.

Bascially the way it works is when the starter cranks, current is sent to the thermo-time switch, and if the temperature is above a certain amount or below a certain amount, the duration of starting enrichment is lengthened.

So you don't have a thermo time switch installed in the crankcase breather cover? This is the metal thing, on the top of then engine toward the front of the CAR, with an oval-shaped base with a hose coming out at a 45 degree angle up and to starboard- the hose is connected to the oil tank at the starboard side of the engine compartment. Some joker could have switched yours with a 64-68 version which does NOT have the provision for a thermo-time. What color is it, shiny silver or dull magnesium? You should see the switch, it has a hexagonal boss so you can tighten it and two connectors, one a yellow wire and one a red/green wire if memory serves. Report back what you see there.

AZ911E · 12-08-2007, 01:37 PM

This is the sensor or switch that is treaded into the oval island. I can't tell the colors of the two wires as the harness as they are covered by a brittle old shrink cover. However the sensor does have writing on each of the six flats of the brass body: [VDO][36 3/4][91161711700][6. 70][+45C][12V 3W]. I metered its resistance at 23.7 ohms at ~40F, 23.7 ohms at ~72F, and 38.3 ohms at ~140F (hot tap water). I would not think it would behave like that is it were bimetallic (on or off). I did not apply voltage to it. and I am trying to attach a photo. Additionally, My old Haynes wiring diagram does not seem to know this gizmo is part of 71E MFI sensors. That's why I'm having trouble troubleshooting this issue. Any other checks? thanks

304065 · 10:32 AM

It's basically TWO bimetallic strips, I think, but I've never cut one open. There's also an internal heater.

One operates above +45C

the other operates below 0C

You can see there are two terminals, one larger than the other. The factory harness has two faston connectors, one larger than the other.

When the igniton switch is turned to start the yellow wire goes to +12V which energizes the starter solenoid, heats up the bimetallic strips in the thermo-time relay and sends +12v to the relay coil through terminal 86 (see DIN 72552). If the temperature is higher than 45C or lower than 0C, the switch grounds relay terminal 85, which energizes the relay, sending current supplied by the second fuse through terminal 30 to normally-open terminal 87. This energizes the cold-start solenoid on the fuel filter console, shown as #12 in the diagram, and you get fuel in the drippers above the stacks.

So at a normal temperature, say 59F, the when +12v is applied to one terminal of the thermo-time, the other should not show continuity to ground, but when the temperature goes above 113F (such as in your 140F test) I would assume you would get close to zero ohms to ground.

Perhaps what you are seeing is the postive temperature coefficient one would expect from metal, e.g., as temperature rises, resistance increases, on the heating element side of the switch. I would treat it like two independent circuits and repeat the test.

What you really need to know is which side does the big faston go to and which is the small one. I don't have my car handy or I would tell you, but some kind MFI soul can certainly oblige us. (or Warren or Grady can tell us from memory!)

The 6.70 is the production date, save this item for concours, don't throw it away, but it's definitely OLD.

Good luck!

AZ911E · 12-10-2007, 06:56 PM

Whoo Hoo. Of course it is two circuits. Here's the resistance check (to ground only)

Large connector: 140F= 98 Ohms; Room temp= ~.7 Ohms; 25F= 0 Ohms
Smaller connector: 140F= 60 Ohms; Room Temp= 24 Ohms; 25F= 22 Ohms

These measurements consistent, going up and down in temp both directions. Interestingly, the hot water test (140F?, maybe 120F?) required me to hold fingers to fire - they both snapped to higher resistance just about when I couldn't hold any longer. How we sacrifice.

I haven't quite absorbed what the measurements mean - but I'd thinking this sensor/switch/timer is OK. Not sure.....

Where's the relay located ("relay coil terminal 86") - I can't get high-enough resolution view of your schematic? (and my "Haynes" is not accurate). The fuses are all good (remember, this enrich system used to work fine).

I'm gonna work the other details, including confirming wiring harness colors, tomorrow (taking day off from work).

I'll get back tomorrow with data. Meanwhile ....A huge thanks. I'm predict I'm gonna get cold starts soon - and its COLD here in Phoenix...dipping into the 50s overnite. Fortunately 70s and sunny most days. Good P weather.

304065 · 05:54 AM

First, wiring diagrams were scanned by our friend and fellow Pelican Sherwood Lee.

http://members.rennlist.com/911pcars/WiringDiag.htm

You can also access the one I posted larger by going to the Pelican main page and clicking on "elec diagrams" at the far left, this will take you to a list, and the '71 is there.

The cold-start relay is located on the engine electrical console at the port-side rear of the engine compartment. It's a standard DIN five-pin relay, cylindrical in shape, if original will have a silver aluminum can, if replaced over the years will be black (or maybe red, if some monkey has substituted a fuel pump relay with internal quench diode).

Those resistance stats look right-- it looks like the smaller connector is the heater because of the positive temp coefficient, and the larger one is the control for the relay's ground. E.g. below freezing it snaps to zero ohms, which would ground relay terminal 85, energize the coil and in turn energize the cold-start solenoid. HOWEVER, it doesn't look like it's going to ground on the HIGH side of temperature, the 45C part.

Yep, I grew up in the valley of the sun, no thermal INERTIA out there-- frying days, freezing nights. Perfect environment for preserving a P-car (except the interior, of course).

72doug2,2S · 72doug2,2S's Garage

Quote:

Originally Posted by john_cramer

WELCOME to the forum. Lots of us 71E guys here.

Best advice I can give you is to use the search function with the terms "cold start MFI" and in particular the users "Grady Clay" and "Early_S_Man." This is, as you might imagine, a fairly popular subject, and has been covered here extensively in about 30 threads-- once you familizarize yourself with the issues, wiring, solenoid, fuel flow, drippers in the stacks, interrupting the circuit with a push button on the dash, etc., then fire away with any questions you may have.

Good luck! I use starting fluid too, mine's been disabled until I can do it right.

Hey all, is there a thread dedicated to the procedure to interrupting the circuit with a push button on the dash? This is done to prevent a possible failure with the system causing too much fuel at the wrong time = fire, correct? I was thinking of an on/off toggle switch. Does it matter what kind of switch and what gage wiring you run?

304065 · 12-11-2007, 05:57 AM

As you can see, there are different thermotime switches, one of which only switches to ground at low temperature.

However, that part number, 91161711700, is the right switch for a 70-71.

304065 · 12-11-2007, 06:23 AM

Good thread with test procedure by Warren.

CIS Thermo Time Switch ????

AZ911E · 12-11-2007, 12:38 PM

I still have no joy. The larger connector (rd/bk stripe, to term 85) should enable the relay to energize the enrich solenoid, because it indeed it is grounded at cold conditions. But no enrich fuel is delivered.

Not cold enough? I packed ice around the installed sensor, and cranked it a few more times. I'm not kidding. Desperate and embarrased.

It could still be the TTS ($150) or the relay ($15). Couple years ago (when this problem first surfaced), I powered the solenoid, and verified that fuel does flow thru. Hmmm. I'm thinking the dash button is looking better. but I want this to work like those smart Porsche engineers designed it. But I'm not ready to just drop 150 bones. I guess I'll trace power thru the harness, now that I know more what to look for. Well OK, I'll start with replacing the 911 615 109 01 relay.

Thanks for the link to the very nice wiring .pdf. It appears to be exactly right for my car. Excellent - now saved in my computer's drive.

Thanks again for the superb troubleshooting advise. I'll keep you posted over upcoming days and weeks. This forum rocks.

Grady Clay · 12-11-2007, 02:30 PM

One thing to keep in mind is the Thermo-Time Switch has an internal heater that heats the bi-metal element. This is powered by the starter wire (yellow). If you keep cranking without letting the Thermo-Time Switch cool (it takes quite a long time unless REALLY cold), it acts as it doesn’t function.

Remember, when you test it out of the car, the housing must be grounded.

Speaking about grounds, The filter console has a ground wire from one of the two large mounting bolts to the nearby ground terminal on the inner fender.

You should also check that the MFI pump has a good ground.

Best,
Grady

AZ911E · 01-01-2008, 11:20 AM

I've resumed my 71E investigation. I can get enrich squirt only when applying 12v to the solenoid on top of the fuel filter. I have replaced the little round relay and fuel filter. I have removed, inspected the the entire electrical panel in the engine bay - all looks good good, and verified its special chassis ground strap. Oddly, there is an empty two-conductor (wire color suggests related to enrich) pigtail just barely visible (aft-facing) under the large connector (aft-most, longitudinal). You'd have to stick you head fully in the engine bay to see it. I thought maybe an enabling jumper (removable for fire safety?) may have fallen out of this connector. No joy, I've metered and jumpered this connector, and nothing seems to return normal enrich function. Function is analog-logic controlled by TTS, powered thru round relay and should enable (assuming all good wiring and connectors) enrich squirt with starter solenoid and dead cold engine for a few seconds.

I know more about this circuit now than I ever though I needed. Nightmares almost. All grounds (MFI pump, engine ground, etc) are OK - not perfect; off a few ohms depending on where and how you meter it. The last thing I think is the Thermal Time Switch (150 bones from our host), and I guess I will order one - soon, after thinking thru everything one more time. That little empty pigtail bothers me - wish I knew why it is empty.

Can any 71E folks look under the engine panel and see it it is connected to anything - like a plug-in (ballasted?) jumper? It's actually easy to disconnect everything off the panel (Permatune forward, small relays aft). Three 10mm nuts liberate the modular panel, and you check it out and clean it up on the bench.

Another observation - the alleged factory wiring schematic is like stop lights in Italy - just suggestions. It is not perfectly tru to the factory wiring in my car. Well, I admit I can be wrong, sometimes getting frustrated with "what were the electrical designers thinking"?

My next thought is crafting momentary manual enrich button during cold craking. I can do that. Like other DIY pelicanites, I'd sure hate that moment when you realize - "yep, that 150 dollar gizmo was NOT the problem".

As before, a hearty thanks to all the advisors thus far. Unfortunately this challenge is not over yet.

pwd72s · 11:27 AM

Not mentioned here is the safety factor....models with the squirters mounted in the air cleaner housing should be disabled, in my opinion. They are engine fires waiting to happen. (edit) My then new 1970 911T suffered an engine fire because of the cold start squirters in the air filter housing...yes, carbs...but the MFI system is as susceptible...