Need help narrowing down the starting problem...

TheCooler · 07-12-2006, 08:05 AM

Heres a list of all things I have working

-Fuel pump works and theres pressure in the rail
-DME relay works
-Spark plugs are firing right

Heres what doesnt work...
-Tach is moving a little bit under 100 rpms but doesnt show real engine speed. It just wiggles a little when I crank the car...I adjusted my reference sensor with a .8mm washer as clarks garage states. I noticed if i disconnect the ref sensor the tach doesnt move at all or if I pull the ref sensor totally out and leave it connected it still gives no reading on the tach (no movement).

I took a resistance reading from pins 25 and 26 I believe and it came to be 990 ohms. Where can i get a oscilliscope from so I can test the ref sensor.

Also when i first grounded to the engine I grounded to a difference point by accident (not near the bellhousing). I started the car and it ran fine. I went back to and noticed my mistake and moved the ground to the proper spot. When I took the nut off the nut and stud was hot...

I hope this did not blow the DME. I took the DME out and resoldered all the connections in it. It looked to have some dryed orange/yellow junk on the top and bottom of the board where the DME plugs in on the resistors? and at some other points on the board. I am assuming this is corrosion or is it a blown out board?

The car will not start now. It has been getting progessively worse. It would first run for a while then stall. Then run for a 30 seconds then stall. Then almost start. Now it wont start at all. Very weird.

Any suggestions on what to do next?

livewirevoodoo · livewirevoodoo's Garage

Cooler... I have an oscilliscope at work I can borrow if needed. No idea how to use it or how to interpret the output, but I'm located in New Haven and would be more than happy to provide any help I can. Let me know.

TheCooler · 07-12-2006, 08:34 AM

pm sent ..thanks

Razorback1980 · Razorback1980's Garage

Sounds more like a grounding problem rather than a reference sensor. When you move the ground back to the wrong location, does it run again?

TheCooler · 07-12-2006, 10:49 AM

It was running fine with the ground on the correct location...but it has gotten progressively worse

Razorback1980 · Razorback1980's Garage

I would check grounds using an ohm meter. If you get any reading other than 0, I would start cleaning grounds starting with the battery cable and moving on to each ground on the car and then coat them with dielectric grease. Ground wires shouldn't be hot for any reason I can think of other than it's not making good contact or heat from the engine. Usually when a connection is warm, it's not making good contact. Fix that before you move on to other things. Pay close attention to the one on the firewall and engine. Develop a checklist (SoCal has posted several here...steal one) and go through the steps. You'll find it. Bad ground will short a DME I'm told, so be sure and fix it.

TheCooler · 07-12-2006, 11:16 AM

I tested my grounds. I get 0ohm readings.

TheCooler · 07-12-2006, 12:26 PM

Injectors dont seem to be firing ....are injectors controlled by the dme?

Razorback1980 · Razorback1980's Garage

Yes, injectors are controlled by DME. Do you have voltage there? Should be 12V on one wire and almost that on the other. You may consider building a jumper around the DME relay or better yet, if you keep a new one around, then install a new DME relay and see if that solves the problem. Check Clarks garage on building a jumper if you do not have a spare DME relay. If you don't have a spare, then I would suggest ordering one. They are relatively inexpensive and do go out from time to time.

TheCooler · 07-12-2006, 02:06 PM

I have like 3 spares. Ive tried them all and i tired bridging the pin 30 with pin 87b. The pump runs fine. I replaced the fuel pressure regulator with a spare also.

Razorback1980 · Razorback1980's Garage

Did you have voltage on the two wires?

TheCooler · 07-13-2006, 09:41 AM

Ok just check the injectors again. One pin has lke 11.5volts and the other has like 12v.

TheCooler · 07-13-2006, 09:43 AM

Im really starting to suspect the reference sensor. I cut open the wiring harness to check out the wires and they seem a little old but still intact...One wire wraps around the other 2 wires and is bare ..this is normal correct?

After messing with the wires the Tach showed an actual rpm reading for a second...then went back to not working again.

Razorback1980 · Razorback1980's Garage

It could be that as the tach should work correctly, but the puzzling part is why are the injectors not working. The DME relay should cycle those without the reference sensor and I am "thinking" (scary I know) that you shouldn't have spark if the reference sensor is not working. Anybody else have any thoughts on this?

TheCooler · 07-13-2006, 10:08 AM

Im thinking possibly the hall sensor controlls spark....

Brando · Brando's Garage

Hall sensor just tells the DME where the rotor is. The DME also controls spark. On later models, it advances/retards on the fly as it detects knock (knock sensor). Start searching around how to test your DME.

TheCooler · 07-13-2006, 10:16 AM

My tach still doesnt work though ...is that because of the ref sensor?

Razorback1980 · Razorback1980's Garage

I think that is usually the case. You may have two problems but the DME and DME relay control the injectors...at least that's my understanding and if they are not clicking, that is one problem but may not be all. Did you have a chance to check voltage there?

If the tach worked well while you were working with the reference sensor wires, one would think the ohms on the reference sensor would not be right. Were the ohms for the reference sensor in spec? I would also inspect the reference sensor wires carefully and make sure they are not broken or making poor contact somewhere. I was helping another guy here (Cava7) when his reference sensor was the problem but he didn't have any spark. After the reference sensor was cleaned the spark returned and everything functioned normally. This may be a second problem.

TheCooler · 07-13-2006, 10:42 AM

The ohms on the ref sensor was in spec.

The casing on the ref sensor is starting to come off where the connector is and exposing the ground wrap....Is this possibly the problem?

Razorback1980 · Razorback1980's Garage

Not sure...but I wouldn't think unless the ground is broken or corroded in some way. Can anyone else answer that question? I know in computer networks we wrap wires to improve the wire so to speak, but I'm not sure about this one. You may try to put some shrink wrap on there though. Of course when I was helping Cava7, his reference sensor was in spec also, but because it was dirty and not sensing the flywheel correctly, it would keep the engine from sparking but you would think if the wiring was bad in some way, the ohms would show that. Have you checked the ohms on the reference sensor wires to make sure there is no electrical degradation in them? Long shot, but it might be something to try.