(see last post for most recent troubleshooting efforts)

Ok, I have a 97 Z28 A4 with 51,000 miles on it, see sig for minor mods.

I've replaced the plugs, wires, coil (twice) and replaced the ICM last night. The car is getting more and more difficult to start. It cranks fine, it predetonates and stumbles and coughs, but never really catches. Getting it home took an extra ten minutes today, just to get it started.

Funny thing is, people say that a bad Opti will misfire, stumble, etc..and I have NONE of that when it does run. Once it's running it doesn't die, throw any codes, or run poorly at all. In fact, it runs awesome! I have the MSD bypassed, so it's not the MSD or the wiring to the coil. The fuel pumps both are running fine, and I know it's getting plenty of fuel.

If it's an intermittent connection problem, (Opti to ICM, or the coil wire) wouldn't it run funny? Or wouldn't I get codes if the Opti was dying? BTW, after replacing the ICM last night me voltage on the dash went up about a volt or two.

I'm about to give up on this car, I've had it about three months now and it's only run well for about 3 weeks of that time.

Can somebody tell me what to do next? I'm going to drop a match in the gas tank if I can't get this fixed.

Thanks guys,
Chris

 

I would make sure you are getting spark to the plugs and check your fuel pressure. I would also clean your IAC and see if that helps.

 

first question i have is:
whats the other fuel pump for?

when your car is cranking but not starting, I would check out your Crank Position Sensor to see if its pulsing properly. then check the optispark for a distributor reference. without the crank sensor pulsing, your PCM will have no idea that you are trying to crank up your car so it will do nothing but chill

someone correct me if Im wrong.

 

are you getting spark when ur turning over your car and wont start?

if you have a scanner. crank the car and observe the RPM on the scanner. see if it registers rpms.

 

Ok, the second fuel pump (inline) was put in because I run a 150 wet shot, and didn't have time to replace the stocker. The fuel filter is new too. When it does finally start I smell lots of raw gas, so I'd be surprised if it didn't have enough pressure.

I don't have a scanner, just a cheapie OBDII code reporter tool that plugs into the diagnostic port. How do I check for Crank Posiiton Sensor signal to the PCM without one, or should I just be taking it to the (gack!) dealer?

I cleaned the TB out a couple months ago and ran a bunch of Seafoam through it, didn't seem to make much difference, but for what it's worth it's probably pretty clean. Besides, if it were the IAC, it would start but idle poorly. I have the opposite problem.

I was thinking of plugging an old spark plug into the coil wire tonight and cranking it, to see if I'm getting spark at least out of the coil. If not then the guess would be that the coil isn't getting the signal from the Opti for some reason, and the Opti to ICM wiring is suspect?

Is there a test or light or something I can do with a multimeter to test the Opti output to the ICM?

 

By the way, I'm somewhat heartened that nobody has yelled, "REPLACE THE OPTI!!!" yet.

/crosses fingers

 

yea just post back what kinda spark you are getting from the coil and then check the spark coming from the spark plug wires ( at least 4)

if the spark from the coil is bad, check the signal to the coil harness. if the signal is good, your coil is bad. but post back the spark tests first.

 

You've got a fuel problem. What do you think happens when the second pump tries to pull more fuel than the first pump can provide. It's called CAVITATION. Try this the next time you have a long cranking problem, squirt fuel in the TB and try starting it.

Having 2 pumps is not the way to go.

 

It ran perfectly fine with two pumps for almost a month until this goofy problem, if there was a fuel draw issue it would have had problems instantly. Besides, our fuel pumps are pusher pumps, so the odds of sucking the stocker dry are slim....and I know several other users on this board and others have the same setup without a problem. If it isn't getting enough fuel, how come it runs hard to redline then?

 

Me thinks slopoke hit the nail on the head. Disconnect your inline pump and see if the stock fuel pump is operating, but here is the kicker, if you have a bad high res signal your pcm will not ground your fuel pump circuit. What exactly is your fuel pressure, because LT1's require 45 to start and 42 to idle. You can check your low and high res crank signals coming from your optijunk with a logic probe.

 

Well, you're gonna love this:

I tested the spark, good all over the place. I ran Shoebox's Opti and ICM diagnostics on a meter, tested perfectly in spec.

Car wasn't starting though, but when it would cough, sputter and choke, fuel vapor came wafting out the intake. I tested the car without the inline in, stocker was humming away fine (still wouldn't start, the inline is just a big plug in the line if there is no power to it.)

Oddly enough, it would start easier and more often with the intake elbow/MAF sensor disconnected. My 5.0 wouldn't even start with the MAF disconnected, let alone idle nicely. Funny.

I would have been surprised if it was a fuel problem anyway, any motor with fuel starvation issues wouldn't pull hard to redline without pinging like mad, if it would pull at all.

I went back to the basics and checked out the indash fuse block, and found the "IP DIMMER" fuse blown!! Replaced it, car started right up, over and over. I feel the need to install a punching bag in my garage now.

I can't imagine for an instant why or how this had the effect it did, as the dimmer fuse/circuit shouldn't have a bloody thing to do with the ignition system, but apparently it does. I was unable to measure the effect at the coil or ICM though.

Anyway, problem solved. I only wasted $140 on a coil and ICM, and am just thankful it wasn't a bunch more. Thanks to all who posted advice too!

Cheers,
Chris

 

just curious if it was hard to start all of the time or just after it sat for a little while?

 

Very interesting fix. i will make a note on theat one!

BTW nothing wrong with two fuel pumps. I have been running mine with two fuel pumps for 5 years no problem.

You can deffinatly tell when you start to loose the stock pump when you have a secondary pump. it makes a horrible noise...then again it gets you home driving and NOT on a tow truck

Go ahead ask me how I know

 

It didn't matter if it was hot, cold, been sitting or anything, 98% of the time it would be very very hard to start, the other two percent of the time it would crank for about two-three seconds and start smoothly.

Yeah, that was one of the goofiest fixes I've done, but I wanted to buck the trend around here of the actual fix or resolution NOT getting posted back into the thread.

Thanks again guys.

 

That is wierd or a coencidence. If starts acting up again check the fuel regulator....that was my thought as I read thru the thread.