Acantor

The meter was on the 200 setting

Acantor

Is it DC ohms? Or is the ohms over to the side of AC? They both read zero when I touch the leads together, but when it is switched to AC, the sensor reads zero, and when it is on the DC setting, it reads open or infinite.

orig944

Put it on DC/Ohms and 20K setting.

Acantor

Ooohhhh I see. It is reading 2.76k I believe or 2.76 on the 20k ohms setting. I tested the old one and it reads the same. This makes no sense. If the sensor is good, what other things determine the amount of fuel to the cylinders? @T&T Racing @orig944

harveyf

What orig944 said. Some meters need to be on a range setting that is greater than the expected value. It is always safe to start at a higher range and then work your way down, to get better resolution.

Acantor

The sensor is reading what it is supposed to (see previous post)

Acantor

I just measured at the dme and I am reading 2.76k aswell (between pin 19 and 13)

harveyf

Congrats on 200 posts to your thread!

Summarize again, completely, the situation where you were able to start the car and have it idle. And then what you do that immediately causes it to not idle.

Btw, please re-confirm that you are getting a tach bounce.

orig944

Some hard won knowledge about using your DMM, but now we know your problem is not the temperature sensor. You are back to looking for something else, like an intermittent connection, short, or DME. Know anyone with an oscilloscope that could look at both sides of an injector while you are cranking?

+1 on the tach bounce check. Also the injectors are powered through the fuel pump relay, perhaps jumpering that would rule it out as a possible issue.

Acantor

Ok, so I installed the new temp sensor and plugged it in and it was like before. I would start and immediately die to what I can only account as not enough fuel. I unplugged it to see if it would start that way as it did the other time. It took a couple of tries but I eventually got it started, the tach read 1k. I was just going to go ahead and brake in my new cam by keeping idle at 2k rpm. About a minute or so into having the car at 2k rpm I started to see smoke and immediately shut the car off to see what it was. It turned out to be the new exhaust manifold gaskets I believe. I went back to start it (temp sensor still unplugged) and it was not getting any fuel to the cylinders (no pulse) but fuel pressure was still at 36psi. At this point, I knew that something else was wrong and did not want to push my luck trying to get it to start again when it clearly does not want to.

Sometimes, with the sensor plugged in, It would start and hover around 200-350 rpm and kind of chop like a crazy cammed corvette (like someone was giving it a little gas and then almost dying again before it would get another short burst of gas). It would try to clear this up and sometimes it did and took the rpm up to 1200. It then tried to bring the idle back down to regular idle speed but it just died.

In my opinion, another fuel/pulse determining sensor is fighting with the temp. sensor making starting the car "hit or miss" when the temp. sensor is unplugged. When the temp sensor is plugged in, the fuel that it is telling the DME to send to the cylinders is not enough to overcome a false reading from some other fuel injector pulse determining sensor.

Could this be a bad reference sensor. What would I look for for "tach bounce"? since the tach is working, doesn't that mean the sensor is good?

I appreciate the help!

T&T Racing

I believe the reference sensors are OK because your Tach functions so speed sensor is OK. The reference sensor sets TDC for DME. The engine starts so it is OK

IMO, the issue is in the wiring for the fuel injectors from the DME or an internal component/crack solder connection on DME PCB. There is an initial 5 amp draw to open each fuel injector coil on the 12v supply and hold at about 1-2 amps, but it pulses may, many times. The DME grounds a pair of injectors, so is an initial of 10 amp and then holding at 2-4 amps. So this pulsing can generate heat in the DME causing issues.
So the first cheap thing to do is to unwrap the wires you taped together after fixing the splices and expose the red/blue wire and get it clear so you can get a good photo of its total exposure on both sides of the 9 pin connector. That is the one wire I could not totally see in the photos. Describe how it is spliced/not spliced by making a sketch of the red/blue wire including any connection into the 9 pin plug and then post sketch as a photo.

Then this information should be able to decide the next step.

Do you have access to a duplicate DME? Have you opened the existing DME?

Acantor

the red/blue wire is untouched. It goes into the 9 pin connector, and there is another red/blue wire leaving the 9 pin connector but the blue stripe is thinner. The only wires that were cut were the green, yellow/red, and the 10 gage red/black one that went to the 2 pin connector.

As for DMEs, I do not have a duplicate and have not opened the existing one.

harveyf

Someone send this man a spare DME unit to try as a test. If I had one, I would. I did have a car once with a bad DME. They are generally rugged but not impossible for it to fail.

T&T Racing

OK,
I would try to open the connector because there is probably corrosion in male/female contacts for the red/blue wire. I would gently pull the connector apart, do not pull on the wires but wiggle each half of the plug, might need small vise grip type pliers and having a second person release the locking tabs.

Acantor

I will do that and post pictures tomorrow morning because I am now heading into work. Say that there isn't any corrosion, what would I do next? It sounds like there may be a fault with the speed or reference sensors as others have suggested?

I am currently rebuilding my dad's old Fluke 87, so hopefully I will be able to rely on a proven meter moving forward.