ivai

Dealing with a no start issue here.

It doesn't seem like the injectors are firing.. I do in fact have fuel pressure but the new spark plugs don't even smell like gas.

Clarks-garage says that on the injector plugs, one terminal should register 12 VDC and one should register 0 VDC, however mine are registering 12 and 10 VDC.. Anyone have any ideas on this?

I tried a different DME relay, no dice.

skene

Since you're getting 12 and 10v on the injectors, you probably have a short in the injector harness. A short there or in the reference sensor wiring will cause a DME fault and the injectors will not fire. See if you can find a broken wire at one of the injector boots or something like that.

Bri Bro

You will read voltage on both side of the Injector (ignition on) until the DME pulses the lead low, then you will see voltage on one side and a pulsing signal on the other. Are you measuring the voltage while your cranking? I wouldn't expect to see much of a difference in voltage on the pins of the injector unless the DME was pulsing on one side. Then, you will read the average voltage on the DME side and that might be around 10 V, depends on the DMV.

ivai

That was measured when ignition was in the ON position, but I wasn't cranking.

Bri Bro

Measure it cranking, the voltage should pulse if your DVM is fast enough to see it. Also, the injectors click and you can feel them cycle. A two person operation at best. A test light should show the pulses and they are cheap.

ivai

Well, discovered something by accident. Tried the light pulsing technique: unplug injector connector, hook up a lightbulb to it, try starting the car. It started!!!

Well damn. After doing some more research, I found that the you have to have resistors in order to have the stock DME power the injectors. The stock injectors (as measured last night) are 5 ohms, and the Siemens 55# guys that I've got are 3 ohms. Doing that means I need two 1 ohm resistors on the connectors 14 and 15, right? I have two 1.2 ohm 25 watt resistors hooked up now (bought them from Fry's), and now the car will fire while turning over, but still not start.

Try unhooking one of the injectors again, and it starts once again on three cylinders. Plug the injector back in, and it still runs, but more poorly (whereas before with no resistors the car would die once we plugged in the 4th injector).

Any thoughts?

skene

Yup, that'll do it. The larger injectors I got came with resistors to wire into the harness. If you do a quick search I think you'll find what the right type of resistors for it are...I can't remember of the top of my head.

ivai

Yup, I already did a search last night.. I found that using two 25 watt 1-1.5 ohm resistors would be sufficient. The resistors I bought at Fry's were not specifically "ballast" resistors, I had found some cases where people didn't need these.

PCinDC

Jeff,
Responded to your PM, here's the math behind this.
Pins 14 and 15 on your DME Harness are each wired to two injectors, in parallel.
Each stock injector pair at 5 ohms per injector presents a 2.5 ohm impedance to the DME due to the parallel wiring.
The 3 ohm injectors present a 1.5ohm impedance to the DME, therefore to equalize this, you must wire a single 1 ohm resistor into pins 14 and 15. It is definitely worth noting that the injectors will fire regardless of the impedance here. Since the impedance presented with 4 3-ohm injectors is slightly less, more current will be transferred over this circuit, and as a result, the DME tends to heat up from the added current. By adding the 1 ohm resistors inline, this is transferred into waste heat at the resistor instead of the DME.

I may have missed this above, but have you used a multimeter to measure the actual impedance value across this circuit? It seems counterintuitive to me that unplugging an injector would cause the car to start.

cruise98

What is your fuel pressure setting? I have read that some will diagnose a bad FPR if you can disconnect one injector and get the car to start. Just a thought.

Do what Paul said and put a fuel pressure gauge on it and adjust it to what the mad chip scientist designed his maps for.

ivai

Paul, thanks for the responses.

I have two 1.2 ohm 25 watt resistors wired inline for pins 14 and 15. I have not checked the actual impedance values across the circuit. I agree that this would be a good test to perform.

Keith, I have a 3 BAR fuel pressure regulator.. The fuel pressure was tested at 40 PSI..

ivai

Just checked for overall continuity on the circuit.. I have it.

Tested from the diagnostic plug to DME plug ports 14 or 15, I'm getting 3.8 ohms on either one with all four injectors plugged in. If I unhook either one of the injectors from a pair, that goes up to 5 ohms.

One other thing about the car starting with only 3 injectors plugged in: From clarks-garage...
"When the fuel pressure runs too high, the fuel injectors draw too much current causing the injector drivers in the DME computer to shut down. Disconnect on fuel injector connector and attempt to crank the engine. If the engine starts, where it would not start with all injector leads connected, the fuel pressure regulator is bad and should be replaced. Disconnecting one fuel injector plug reduces the injector driver current sufficiently to get the injector drivers to fire"

I think I either have too much fuel pressure or not enough resistance. Any other suggestions would be helpful though.

ivai

Another update, the car does in fact run with 4 injectors in. It runs poorly, but it runs. I unplug one injector, and it runs much better, but you can still tell that the car is in "limp mode" (3 cylinders).

To correct my values in my last post.. I'm getting 3.0 ohms across the circuit when I have a pair of injectors hooked up, and 4.1 ohms with one out of the pair of injectors hooked up.

I re-tested fuel pressure, right at 42psi (3 BAR).

Now verifying that the MAF is wired/working correctly.

ivai

MAF is wired correctly.. timing is correct.. I doublechecked continuity through the injectors circuitry.. tried a different DME..

Argh, this is so frustrating. What am I missing?

Bri Bro

You are running aftermarket chips with the MAF so do you have the DME set to the size of the injectors. And, the DME will drive he injectors without the resistors, the resistors give it a little margin if you run the injectors at a large duty cycles for long periods of time.