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Thread: Thermo Time/Cold Start Issues...tried the FSM tests....help

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    Default Thermo Time/Cold Start Issues...tried the FSM tests....help

    Hey guys....I'm trying to fix what is basically an extended cranking problem on a 280 that's been warmed over with a cam and some head work. My customer wants it to start a bit quicker on initial start up. I figured it was just an issue of the engine building up some compression first with the larger cam but after digging in a bit it looks like the cold start injector isn't working.

    I followed the FSM tests...if I jumper the injector off of the batter directly it cycles and squirts a small amount of fuel...which I assume is ok since the fuel pump isn't running when I jump it. However I ran a meter on the thermo switch and it didn't seem to meet the specs outlined by the FSM. My local Nissan dealer was able to get me another switch and I popped it in there this morning and sure enough the injector still isn't firing.

    I put the ohmeter back on the new sensor and it's still out of spec based on their requirements. With the No 45 pin probed and the switch body I'm only seeing about 55 ohms. They call for 70-86. The water temp should be below the 58* spec as air temp in the shop is about 55* right now and I haven't run the car in days. Is it possible my new sensor is no good? The thermostat housing was ceramic coated however if I run a continuity test between the thermo time sensor body and a chassis ground it's showing continuity so I think the sensor is grounding properly.

    What's going on here??

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    You might be losing fuel pressure when the pump is off. Could be the FPR or the check valve in the fuel pump. The cold start valve is probably fine. You can check it's operation by jumping the connector pins with a nine volt battery.

    That's a fine line between 55 and 58, and that spec is for the thermotime switch. Which could also be bad or have a bad connection. Current for the CSV runs through the thermotime switch.

    I would check fuel pressure first. At 55 degrees the engine should still stat pretty easily. Mine does, since I got an FPR that holds pressure, and I do not have a CSV.

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    Zed....the spec for the Thermo Timer is 70-80 ohms....so my reading of 55 seems to be well out of spec....but like I said that's on a brand new switch.

    As for the fuel pressure dropping off....could be. I just installed a new Nissan fuel pump so I'd assume the check valve is good. The regulator however I didn't know could bleed off. How can I test this?

    Also I stated above the csv works if I jump it directly off of the battery so I'm ruling that out. If I put a fuel injection noid light into the connector for the csv I still get no pulse.

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    I interpreted "sensor" as CSV, not thermotime switch. It's a thermal switch, not so much a sensor. Oops.

    I was just messing with a CVS last night, with an ohm-meter and a heat gun. It went from ~ 64 ohms cold, to open circuit hot. The resistance is from a heating element in the switch, like the same in the AAR. Most AARs measure ~ 60 ohms also. The switch is designed to get hot when the starter circuit is active so that you don't flood a cold engine. There's not much to it, the CSV solenoid does not need a lot of current to move.

    Testing requires a pressure gauge between the rail and the filter. Measure pressure, start the engine, then monitor pressure after shutting the engine off, and right before attempting to start. The regulators do get old and the seats don't seal. I have a few in my garage that regulate fine but don't hold pressure.

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    Gotcha. I'm still thinking something in the CSV circuit however since the harness to the actual valve gets no electrical pulse.

    I just spoke with Mike at Banzai Motorsport and he suggested looking into the CTS as it may not be telling the computer it's cold enough. The actual CTS is new within the last year but maybe it's a wiring issue?

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    The CSV only gets power when the Start circuit is active.

    Measuring fuel pressure is not difficult and you'll save yourself a lot of time by just getting the gauge and doing it. But, on the other hand, looking at all of the stuff that's not the problem is pretty educational.

    If you had a CTS issue it would be manifested after starting also. Good luck.

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    Ok I just spent about 2 hours going through different tests. It looks like I'm getting no power to the cold start circuit from the ignition switch as best as I can tell. I have continuity from the csv to the ignition relay on both sides of the relay. And I have continuity from the csv to the connector going into the fuel system controller. This seems to leave me with the wiring going from the fusible link to the ignition switch.

    The fusible link is good and I seem to have continuity from the fusible link to the ignition relay...so I assume it's bad from wherever the fusible link line branches off into the ignition switch. I can't find continuity from the fusible link into any of the wires going into the ignition switch but according to the FSM there whould be one going in and then when the ignition switch is in the start position it sends power from that input out to the CSV system.

    Does anyone know which wire into the ignition switch should be coming from the fusible link? I'm also not sure how the car would start and run with no power coming in from the fusible link?

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    Looks like the Black with Yellow should be my wire from the Positive Battery Fusible Link eventually ending at the ignition switch...however this isn't showing continuity all the way through.

    I found a wiring diagram for a 75 but the wire colors don't seem to match up. My fuel injection relay has blue wires going into it instead of red like the diagram shows...however it looks like my red wires coming in from the engine bay might switch over to blue in the harness right before it branches out 6" into the fuel injection relay...not sure why. My continuity from the fusible link to the upper part of the relay at the blue (red) wire is good....but on the lower half of the relay the continuity doesn't continue back out of the blue (red) wire. There are two small "nubs" on the bottom of the relay that nothing can connect to and I have continuity there. Does this mean the relay is bad??

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    Ok just an update.....and unfortunately I have 2 seperate threads going on this issue now...other is in the Help Me section.

    I have the csv problem narrowed down to a specific area at this point. The fuel injection system relay is supposed to get 12V from the ignition switch in the Start position on a black/yellow wire at the switch which I have. From there it should travel down to the relay passing through a 4 wire connection on it's way. At this connection the wire color has changed from black/yellow to solid yellow. By the time the wiring hits this point I've lost my 12V signal. If I jumper from the switch down to this point the csv works perfectly.

    Does anyone know where this wire travels and splits off from the ignition switch down to the 4 wire connector? I followed it up under the dash but it goes above the pedal bracketry and behind the speedo and tach where I can't see it anymore or unwrap any more of the harness protection.

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    You seem to be using the forum to get advice on work that you'll be getting paid for and which you should probably be capable of completing, as a professional automotive restorer. You need to at least make it worth people's while to respond. At least do the things that they suggest, even if you don't believe that the advice is helpful. Have you checked fuel pressure yet?

    Some of your comments don't really follow known facts either - "The fuel injection system relay is supposed to get 12V from the ignition switch in the Start position on a black/yellow wire at the switch which I have." What really happens is the fuel injection harness gets power when the key is On and at Start. The CSV works when the key is at Start and the thermotime switch is cold. It might be grounded through the thermotime switch or it might powered through the thermotime switch. It would be a good thing to figure that out through the FSM diagrams. Many of the Zs systems are activated through grounding and have power available all the time.

    If you mentioned the year car you're working with, someone might have some help also. There are several full-color, detailed, wiring diagrams out there, free.

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    Zed...you are correct this is a customer car, however I have a lot of hours into this issue...of which I will not be billing my customer for. I do not claim to be an expert on every car out there....especially when it comes to electrical issues. Being in the restoration and not the repair business per say my expertiese lays more in refinishing however I'm fully capable of performing mechanical work.

    I should have mentioned that the car is a 75 in my first post but I referenced it (not very well) in my #8 post.

    I understand that the injection harness gets power in both the Start and Run positions, however the csv and thermotime both only receive power in the Start position....on the black/yellow ignition switch wire that I referenced. In the run position the harness receives power on the red/white wire. The thermotime and csv should only have power when in the Start position and the csv operates based on the grounding of the thermotime, which is based on if it's heated up or not from extended cranking...in the Start position. It's basically a way to keep from flooding the engine in an extended cranking situation...although it only shuts down the csv and not the actual injectors I think.

    So unless I'm wrong this system does not have power available all the time....since it's a Start only function...running off of the black/yellow wire...which loses power once the key returns to the Run position. This brings me back to my question in my previous post....do you know where the black/yellow wire from the ignition switch travels up to before splitting off to the yellow (what the FSM diagram still shows as black/yellow)? I believe I have a break in this run of wire somewhere causing my lack of power to the thermotime/csv circuit....but as I said I can't follow the wires up under the dash. I was hoping someone would know where they may split off and I may be able to access them from.

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    Found my broken wire. Looks like someone accidently damaged it installing an aftermarket radio. Everything seems to be in working order now.

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