Elusive starting issues

[Viprklr]

Finally got some quality time in on my dad's 87 GN. The car tends to not want to start after it's been warmed up. Here's what I found.

ECM 1227148
Prom ID ACXA

Has Ultrachip V. CTW87.50 (set on stock setting)

Fuel pressure set at 45psi (verified with 2 gauges)

Has an issue with cold start. Doesn't want to stay running without a little help from the go-fast pedal.

All 6 injectors read 12.1-12.2 cold.

Replaced coils and wires.

Tried to adjust TPS and IAC but apparently didn't take. Maybe due to the following:
We had 2 different Snap-On scanners hooked up to verify these results. Both showed the same crazy stuff.
Whenever the fan comes on several of the sensors start reading crazy numbers and jump around. For example, CTS goes from 199F to 30F, TPS goes from .54 to 4.30, MAT goes from 52F to -13F, RPM's goes from 1000 to 4890. They all jump around.
During this time the engine doesn't exhibit anything as being wrong.

We toned out all 3 or 4 grounds on the ECM D connector. For grins we ran a separate ground from the battery to both the chassis and engine. No change in displayed craziness.

With the TPS set at .44 the IAC was at 82 steps. RPM's were at 1000. When I set the TPS and minimum air I had .50v and 500 rpm. As soon as the IAC got reconnected the idle went to 1000 rpm, TPS went to .56 and the IAC steps wouldn't drop below 52.

We were unable to duplicate the hot start issue this time. It did act a little differently though. It had trouble starting but did start whereas before it was acting completely dead.

A couple of other points:
The fuel pump is priming every time.
Injector voltage seems a bit low at 9v.
MAT was at 52F. I would think that should read higher due to heat soak in it's mounting location. The garage was ~50F.

Disconnecting the battery HAS gotten the car to start during the no-start condition in the past.

I think that's everything.
Does this look familiar to anyone? Suggestions? Help?

 

[Viprklr]

No ideas?

 

[turbojd]

Did you check the ignition module and coilpack? Could check the crank sensor and see if it's loose, check the top of cam sensor. How are the condition of your fuel injectors? Check spark plugs for fuel.

 

[darkred87T]

It sounds like some kind of ground problem going on there with what you described about the fans comming on. I'm sure you checked all the grounds going to the back of the block? There are several of them and they should be tied in either to a bell housing bolt or rear intake bolt on the right side of the engine. One of them is a ground for the fan.


If that's not the problem, maybe you should try the "spring cleaning" on Turbo Regal Web Site.

 

[TurboBuRick]

Those kind of problems can drive you crazy. Much more easy to find if it would just crap out all together. Need to find out if it's spark or fuel causing the issue. That would give some direction to go in.

Pick up a in-line ignition tester and throw it on one of the spark plugs. That will give you something to look at as far as spark goes. If you find spark drop out to be the cause, replace crank sensor.

Good luck!

Rick

 

[Viprklr]

Have not checked the cam sensor yet.
We have replaced the coilpacks.
Ignition module is fine.
We checked the grounds in the "D" connector harness at the back of the ECM on several of the "screwy" sensors and had continuity.
Used a jumper cable to create new grounds between the battery and block/chassis with no apparent difference.
The injectors "aftermarket" all cold ohmed out at 12.1 - 12.2 and all click when running. There is only 9v across the drivers though. Is this low?

 

[bison]

When you get crazy numbers like that the ecm is usually the problem. Id switch it out with a known good one. You need to verify the minimum air rate. Reset the IAC and make sure its set. The car should idle without the IAC open or it will stall on decel and when there is a quick drop in rpm. Id get a new Turbo Tweak chip in there too. Cold start will be improved.

 

[darkred87T]

To reiterate my previous post...

Whenever the fan comes on several of the sensors start reading crazy numbers and jump around.

Did you check the ground wires that are terminated at the back right side of the engine block? One of them is for the cooling fan. If something (like the fan) isn't properly grounded, it may find ground elsewhere which could really screw things up, no?

 

[Viprklr]

Turns out the problem ended up being a bad battery. Who would've figured.