Dwell Stuck at 50% am I correct to suspect the O2 sensor?

[spikeygg]

By hot cams, you mean non-OE cams? Timing could be a factor.

yeah, non-OE cams. I set the timing back when I finished the rebuild a few years ago but it's a good call out. I should verify that the timing is correct. Any idea what it should be for non-OE cams?

[spikeygg]

I find that anything other than an analogue meter is hard to set the mixture with but I'm not that smart. Watching that needle swing makes it easier (for me anyway).

As far as your cold start goes, two or three things;
Check your battery voltage and charge if needed. Sounds like it's cranking slow and your volt gauge looks pretty low. I found with mine that it started a lot easier when the alternator was functioning properly. Cleaning the ground on the frame below the expansion tank could also help as well as the one on the radiator bracket.

Cool, I'll check these spots. Regarding the voltage, I always have the car hooked up to a battery tender so it *should* be charged. I took the battery and alternator out to AutoZone about 6 months ago to have them both tested and confirmed that they were both in good working order.

Also look at the o rings in the primary pressure regulator in the fuel distributer. If they are old just replace them because even the smallest imperfection or damage can cause a hard hot start but if they are really bad it will also affect cold start. Thing is there is no way to really check them without removing them and they get hard and brittle when old. It's a cheap and very easy fix but be sure you know that the plunger is spring loaded when you remove that nut.

I would not worry too much about mixture setting right now. Once you fix your cold start issue and possible other problems such as a vacuum leak, etc. The mixture is usually the last thing you do.

As it turns out the hot start is easier than the cold start in this case. Should I skip the o-rings based on that? I've never opened the fuel distributor before... I'll have to see if I can find a youtube video on that.

[spikeygg]

Hard cold starting usually means a problem with the cold start valve or other associated parts like the TTS or the wiring. If you have the duty cycle set, leave it alone. If you have after-market cams you may need to adjust the base timing. While checking the timing you should check the mechanical and vacuum advance to make sure they are working properly. The dwell or O2 sensor has no effect on cold starts. If the battery or any connections are not good and the voltage drops low enough the ignition ECU won't work so that means no spark and no start.

I can check the timing easy enough but how do I check the mechanical and vacuum advance?

The main thing that controls the motor during warm-up is the CPR. To test if the cold start system is working, do the plug swap. If the cold motor starts easier then figure out why the CSV is not working right.

Maybe I'm missing something but you said previously that the "plug swap" was intended to check hot start issues, not cold start issues:

The "plug Swap" is mainly intended to start the motor if you have a hard hot restart problem, not a cold start problem. If doing the plug swap helps fix the cold start problem that means you have a wiring problem or a bad TTS switch in the cold start valve system. When cold the cold start valve is supposed to be opened during cranking by the Thermo-Time Switch. Doing the plug swap bypasses the TTS and the wiring, running the Cold Start Valve directly. Once the car starts you must quickly put the plugs back or you will flood the motor with excess fuel. The plug to the TTS has a polarity and MUST be installed correctly or you will burn up the TTS. The TTS MUST be grounded, installing it with Teflon tape is a bad idea.

I guess you're suggesting that I can verify that it's not because of the CSV system by doing the "plug swap"? I'm reading through the Cold start issues page on the DeLorean site and it mentions some of this.

It says: "The heater should measure about 50 ohms to ground, and the switch connection should measure a dead short (0 ohms) to ground when cold and open (infinite) to ground when hot. NEVER apply a test voltage to the TTS." Doesn't setting the voltmeter to resistance measurements automatically apply a voltage in order to read resistance? If so, how are you supposed to measure the resistance without applying a test voltage?

[vwdmc16]

yeah, non-OE cams. I set the timing back when I finished the rebuild a few years ago but it's a good call out. I should verify that the timing is correct. Any idea what it should be for non-OE cams?

Did the cams come with a set up card? Only real way to change cam timing is to re drill holes in the cam sprockets.

Did it start fine when you first got it back together after the rebuild?

[Bitsyncmaster]

Crap, I was worried about that. I can measure +Duty and/or -Duty on the scope and I chose +Duty because I wasn't sure if it should be high time or low time. Unfortunately, I removed my WOT switch from my car -- it was broken and causing other issues. Can I just ground the WOT pin to enable the WOT mode? Or maybe I need to short the two pins together? That should be an easy way to check.

Yes you would need to connect that signal to get 60% dwell for checking your scope reading. You get 50% at warm up but that won't show any inversion.

[David T]

Whoever supplied the cams usually gives instructions on how to install them and what to set the base timing to. Refer to M:01:04 for the specs for timing advance. The "plug swap" forces the cold start valve open. Useful to troubleshoot hot and cold start problems. Before testing the TTS, try the plug swap. If that gets the motor to start easily then you can check out the TTS and the wiring. The manual warns against putting 12 volts on the TTS. A resistance meter is only going to apply about 1 1/2 volts, that is safe to do. For a better look at the cold start system refer to D:01:10 and D:04:06

[DMC5180]

Most of The high lift cams have base timing set from 16-18 BTDC. But whom ever you bought them from should give you guidance.

[vwdmc16]

Most of The high lift cams have base timing set from 16-18 BTDC. But whom ever you bought them from should give you guidance.

To be clear are you talking about cam timing or ignition timing? 16-18 Btdc sounds like ignition

[spikeygg]

Did the cams come with a set up card? Only real way to change cam timing is to re drill holes in the cam sprockets.

Did it start fine when you first got it back together after the rebuild?

I don't think I have any card for it. In my possession, the car never ran correctly. When I got it, it was running on 4 cylinders and the WOT switch was broken (always on). I hypothesize that the previous mechanic that put it back together didn't realize the WOT switch problem and backed the fuel mixture screw all the way down. I found a bunch of stuff, went through the car and upgraded a bunch of stuff in the process (like the crappy wiring). It runs much better now but there are some things I need to wrap up like this stupid cold-start problem.

I don't want to change the timing of the cams, I guess I'm wondering what the base timing should be on a car with aftermarket cams -- maybe I need the card.

[spikeygg]

I just did the plug swap and it started right up.

So, I think that means the cold start valve is good, right?

After that I tested the pins of the TTS to engine ground and found that one pin was about 30Ω and the other was 0.2Ω -- both of those values sound right. The electrical clip that clips into the TTS sensor is badly damaged, I wonder if that clip isn't making a good contact to those TTS pins...

What else can I check?