I have a couple of CIS specific questions and was wondering if anyone on the list might be able to help?

Doug C

Hi Doug

what are the questions?

First is a question about the wiring if you can help. The brown/black wire that connects the 2 sensors (that fit between the intake runners...1 on the passenger's side and 1 on the driver's side) were does it plug into at the relay board? I believe these sensors are WUR and Thermo Time Switch or AAV (don't know what that stands for). Anyway they seem to be connected by the same brown/black wire but when I trace this wire through the wiring harness it ends atop the 12 terminal plug at the relay board and is not part of the plug. It ends there with a quick connect electrical connector. The PO of this engine/wiring harness had it all installed in a 914 and it worked great, but the PO doesn't recall how it was installed because he didn't build the car. Does those sensors need switched power? I have no clue and would appreciate any help.

Doug C

Brown wires are ground. Might help if you tell us the year and engine size. I can look it up on the wiring diagram. The Cap'n

WUR = warm up regulator... has fuel lines running to it
AAR = auxiliary air regulator.. has larger dia. vacuum hoses

These have a power and ground wire and are usually powered off the fuel pump relay so there is only power with the engine running

Thermo time switch is for the cold start valve...only has the electrical connector...there is one wire that only connects the thermo time switch and the cold start valve...the second wire also connects both and gets power from the starter solenoid circuit.

2.7 from a '77 911s. This wire is brown with black bands every inch or so. Thanks for looking up the wiring for me, those schematics seriously bogle my mind.

Doug C

The WUR is a box that's perched on the top of the case, not far from the thottle body. Fuel and vacuum lines, plus one electric wire that's hot with the ignition. The AAR is the fast idle control valve. It allows extra air past the throttle when the engine is cold. Should have two vacuum lines and one electric wire, also hot with the ignition.

The thermotime switch controls the cold-start valve, which give a shot of fuel during cranking only if the engine is cold. The cold start valve is mounted to the manifold below the throttle body. As I recall, the thermotime switch was mounted at the fan end of the engine on my 73.5, but it may have moved around for later years.

The schematics aren't hard to figure out once you have some idea of what the various bits do. Pretty much everything you've mentioned is only there for cold starts and running during warm-up.

OK, guys I'm getting confused trying to learn the names of whats what..Basically (and simply) the 2 pieces that I'm talking about are the ones between the intake runners, one on each side. You guys are saying that they need switched power when the ignition key is turned on, right? OK, then could this brown/black wire be plugged in to the relay board at the location for the stock 914/4 FI? There is a 4 prong plug on the board that's not being used, one of the progs lights up my tester when the key is on. Or like the Cap'n suggested this could be a ground wire.

Doug C

QUOTE (DougC @ Oct 6 2005, 12:28 PM)

OK, guys I'm getting confused trying to learn the names of whats what..Basically (and simply) the 2 pieces that I'm talking about are the ones between the intake runners, one on each side. You guys are saying that they need switched power when the ignition key is turned on, right? OK, then could this brown/black wire be plugged in to the relay board at the location for the stock 914/4 FI? There is a 4 prong plug on the board that's not being used, one of the progs lights up my tester when the key is on. Or like the Cap'n suggested this could be a ground wire. Doug C

The four prong plug on the /4 relay board is for the D-Jet ECU. Terminal I has switched power (normally powers the ECU). II and IV have power when cranking. III is normally FROM the ECU, so it's not useful to you.

Wire color isn't always helpful. I don't recognize brown/black as a normal color combination. Plain brown is ground. What do the brown/black wires connect to? Take photos or try to describe what they're connected to.

Brown/black wire connects first to the WUR (mounted on intake runner above cylinder #1) then carries on to the AAR (mounted on the opposite side of intakes). The end at the relay board is just free with a female quick connector.

Doug C

Call me. I have the book open in front of me. 805 925 1993. The Cap'n

Cap'n I didn't get your message til after I left my computer for the weekend - thanks for the offer to call you on this matter.

Here's my latest finding on my non-starting 2.7L CIS motor :
This weekend I learned that my Main power relay was bad..I replaced it and the engine and starter turns everytime with gusto. Sounds like it'll start any second, but doesn't. It acts like it's not getting fuel after the engine initially tries to start up..If I try giving it any fuel it immediately dies. Well, I think I may have found a possible cause but I'm not sure. The electrical connector to the Air Meter under the air filter box. That connector was broken so I had to replace it. OK, it has two wires to it...one solid brown and the other brown w/black (remember this one?). That's the wire that is loose at my relay board. Well, I figured it needed switched power so I plugged it into term I for the stock /4 D-jet ecu, since it is switched power. Upon trying to start the engine, that wire started to smoke and actually melted it's sheathing. So, I think I hooked that wires of the electrical plug (at air meter) backwards even though I called myself paying attention. Could The Air Meter sensor be causing the injectors not to spray fuel?

Doug C

The 2.7 CIS is "basic" CIS. It requires almost no electrical power to start and run. Later versions (used on the later SC) had an O2 sensor, some electronics, and a control valve, they all required switched power. The 2.7 version, however, doesn't have this. With no power, you'll find cold starts to be harder, but not impossible. The cold start valve won't open, and the WUR will take much longer to stop adding "cold" enrichment. However, unless the temp outside is below 50dF, you shouldn't have any trouble starting the engine dead cold with no cold-start system.

Only the fuel pump and the ignition need power. The fuel pump can be checked by just feeling it with the power on. It should vibrate. You can also use a pressure gauge (rated for at least 10 bar or 150psi) on the fuel line between the pump and the fuel distributor. It should show 6-7 bar or around 80-100psi with the fuel pump on. If it doesn't, your fuel pump is bad, or perhaps your filter is terminally clogged. If you suspect the filter, place the pressure gauge just after the pump (before the filter).

If you have fuel pressure, take the airbox off, and take off the snorkel between the air meter and the throttle body. The air plate should be clean, and should move VERY easily (it goes up, so reach into the airbox and push it up with a finger). If there's any resistance, it's possible your fuel distributor is gummed up. Don't try to clean it yourself.

When starting CIS, you need to keep your foot OFF the gas while cranking. You may need to blip the throttle a tad AFTER it catches, but don't give it gas while it's cranking, or you'll discover why the airbox pop-off valves are so popular.

QUOTE (DougC @ Oct 10 2005, 11:08 AM)

Cap'n I didn't get your message til after I left my computer for the weekend - thanks for the offer to call you on this matter. Here's my latest finding on my non-starting 2.7L CIS motor : Well, I think I may have found a possible cause but I'm not sure. The electrical connector to the Air Meter under the air filter box. That connector was broken so I had to replace it. OK, it has two wires to it...one solid brown and the other brown w/black (remember this one?). That's the wire that is loose at my relay board. Well, I figured it needed switched power so I plugged it into term I for the stock /4 D-jet ecu, since it is switched power. Upon trying to start the engine, that wire started to smoke and actually melted it's sheathing.

Brown is GROUND. NEVER POWER IT UP! That's a grounding circuit for the fuel pump relay!!!! If you leave it unplugged, the fuel pump should run with the key on. If it's plugged in, the FP runs only when air is passing through the sensor housing. Safety feature. You REALLY need to look at the wiring diagram. REALLY. I fear you'll burn the sucker to the ground before you ever get it started. The Cap'n

I can definately hear the fuel pump running.. Is the FP relay the same for a 914/4 and a 2.7L six with CIS? I may need a different relay.

Doug C

QUOTE (lapuwali @ Oct 10 2005, 12:04 PM)

The 2.7 CIS is "basic" CIS. It requires almost no electrical power to start and run. Later versions (used on the later SC) had an O2 sensor, some electronics, and a control valve, they all required switched power. The 2.7 version, however, doesn't have this. With no power, you'll find cold starts to be harder, but not impossible. The cold start valve won't open, and the WUR will take much longer to stop adding "cold" enrichment. However, unless the temp outside is below 50dF, you shouldn't have any trouble starting the engine dead cold with no cold-start system. Only the fuel pump and the ignition need power. The fuel pump can be checked by just feeling it with the power on. It should vibrate. You can also use a pressure gauge (rated for at least 10 bar or 150psi) on the fuel line between the pump and the fuel distributor. It should show 6-7 bar or around 80-100psi with the fuel pump on. If it doesn't, your fuel pump is bad, or perhaps your filter is terminally clogged. If you suspect the filter, place the pressure gauge just after the pump (before the filter). If you have fuel pressure, take the airbox off, and take off the snorkel between the air meter and the throttle body. The air plate should be clean, and should move VERY easily (it goes up, so reach into the airbox and push it up with a finger). If there's any resistance, it's possible your fuel distributor is gummed up. Don't try to clean it yourself. When starting CIS, you need to keep your foot OFF the gas while cranking. You may need to blip the throttle a tad AFTER it catches, but don't give it gas while it's cranking, or you'll discover why the airbox pop-off valves are so popular.

A lot of what you're saying here is wrong. The 2.7 CIS requires power, as do all basic CIS systems, to the control pressure regulator (WUR), the auxilliary air valve, and the cold start valve system. IIRC, on some 2.7s there's also a circuit for cold start enrichment so the throttle is opened slightly without the need for a throttle position lever. Without power to these systems, cold and warm mixtures aren't set, idle speed is too low cold or too high warm, and the engine will be a real bit*h to start on cold days. The Cap'n

If the fuel pump is running, the relay is fine. Relays are relays, for the most part. If there's a CIS specific part, it's the switch inside the air meter. As the Cap'n says, this is a safety feature to shut off the pump if the engine isn't running. If it's disabled, the car will still start and run.

Your problems are not electrical, at least not for the CIS. If your ignition works, and your fuel pump works, that's all the electrics you need to worry about. Any no-start condition now is something else: bad fuel pump (not enough pressure), or bad fuel filter (clogged), or bad fuel distributor (gummed up).

Is that true even if the PO by-passed the fuel pump relay because he was using carbs? The reason I ask is because I actually pulled the FP relay and turned on the key...could still hear the FP running until I turn the key all the way to the final start position, at which point I no longer hear it (in any situation).
Sound the same weather there is a relay installed or not. BTW, thanks again guys.

Doug C

You can also run the motor without the electrical conections made to the WUR for now if you need to. They help the WUR to warm up faster is all.

Even the AAR is the same, your engine will just idle higher for longer.

I would scratch hooking up anything but the fuel pump until you get it running. CIS from a 2.7 should run from nothing more than the fuel pressure.

QUOTE (Cap'n Krusty @ Oct 10 2005, 12:19 PM)

QUOTE (lapuwali @ Oct 10 2005, 12:04 PM) The 2.7 CIS is "basic" CIS.  It requires almost no electrical power to start and run.  Later versions (used on the later SC) had an O2 sensor, some electronics, and a control valve, they all required switched power.  The 2.7 version, however, doesn't have this.  With no power, you'll find cold starts to be harder, but not impossible.  The cold start valve won't open, and the WUR will take much longer to stop adding "cold" enrichment.  However, unless the temp outside is below 50dF, you shouldn't have any trouble starting the engine dead cold with no cold-start system. Only the fuel pump and the ignition need power.  The fuel pump can be checked by just feeling it with the power on.  It should vibrate.  You can also use a pressure gauge (rated for at least 10 bar or 150psi) on the fuel line between the pump and the fuel distributor.  It should show 6-7 bar or around 80-100psi with the fuel pump on.  If it doesn't, your fuel pump is bad, or perhaps your filter is terminally clogged.  If you suspect the filter, place the pressure gauge just after the pump (before the filter). If you have fuel pressure, take the airbox off, and take off the snorkel between the air meter and the throttle body.  The air plate should be clean, and should move VERY easily (it goes up, so reach into the airbox and push it up with a finger).  If there's any resistance, it's possible your fuel distributor is gummed up.  Don't try to clean it yourself. When starting CIS, you need to keep your foot OFF the gas while cranking.  You may need to blip the throttle a tad AFTER it catches, but don't give it gas while it's cranking, or you'll discover why the airbox pop-off valves are so popular. A lot of what you're saying here is wrong. The 2.7 CIS requires power, as do all basic CIS systems, to the control pressure regulator (WUR), the auxilliary air valve, and the cold start valve system. IIRC, on some 2.7s there's also a circuit for cold start enrichment so the throttle is opened slightly without the need for a throttle position lever. Without power to these systems, cold and warm mixtures aren't set, idle speed is too low cold or too high warm, and the engine will be a real bit*h to start on cold days. The Cap'n

But it will start (as long as it's not too cold). I'm trying to convince Doug that his no-start condition is NOT electrical, because I don't think it is. Having all of the warm-up stuff disconnected won't prevent it from starting and running, it just makes it harder to start when it's cold out. The basic CIS system itself doesn't require any power at all, and if it's 80dF out, you won't even notice the warm-up stuff doesn't work.

The warm mixture will be set fine once the WUR is warmed up by the engine itself, it just takes longer. The AAR should also close once the engine bay gets hot enough, and will only cause a high warm idle if it doesn't. It won't affect mixture at all. The cold-start valve only works during cranking, and the extra fuel isn't required until it gets very chilly (below about 50dF, from my own experience).

Basic diagnostics: ignore the ignorable when trying to track down a problem. Only pay attention to the ignorable when you exhaust all that's not ignorable. For a no-start, warm-up stuff is ignorable unless it's COLD out. Once Doug has the engine starting and running, THEN he needs to make sure the warm-up stuff is operational. Chasing warm-up system electrical problems when the engine won't even start, however, is only ignoring the real problem.

James - Are you saying that the AIR METER electrical connection does not have to be connected? Not talking about any of the other CIS electricals.

I was thinking it was an electrical situation because I found that my main power relay was bad (obviously).

Doug C

The air meter connection controls the fuel pump relay. If the fuel pump is wired to always be on the with switch, then the air meter switch and the fuel pump relay are superfluous.

Doug,

If you would like, I can come over thursday night and we can sort the wiring out.


Call me if you want to.