Please help me diagnose my no start issue. 5.2 F355

I performed my engine out major service over Xmas break, did not have the issue prior.

The car ran and drove after the service.

About a week after the service I parked the car in the driveway to reinstall the ECU cover. When I was finished the car would not start, it cranked fine but no start. My CEL was on due to my bypass valve, I noticed it was not illuminated. I decided to take a shot in the dark and disconnected the wiring harness from the ECU (after switching off the battery). When I turned the key to the ON position the CEL lit up after maybe 8 seconds and I heard the fuel pump at that time. I turned the key and it fired up.

This happened maybe 6 or 7 times since and the fix has always been the same. Today it happened twice, the second time I was unable to get the car started (no CEL either). Luckily I was in my neighborhood and after a quick tow and push from a friend the F355 is safely back in it's garge stall.

I will add that my interior dome light is constantly on whenever the battery is switched ON. I noticed this after reinstalling the drivetrain but figured it was because my engine cover was not installed. Even after reinstalling the deck lid the light remains ON. This may prove to be connected to my issue, not sure.

Another thing to note, my alarm LED is always lit solidly when driving. In the first few drives after the service the light would not be lit, sometimes I would not need to use the button on the fob to allow the engine to crank. Recently it has been operating as normal, LED constantly lit while engine is running.

I will go out and check the fuses next but wanted to get this issue under everyone's eyes for consideration ASAP.


Feel free to throwyamy ideas out, I welcome an easy fix even if it's at the expense of my mechanical credibility.

 

You mean when the car no starts you disconnect the motronic ECU, plug it back in and the car will fire up normally?

I fly into Tuscon to race at Indie in 2 weeks. See how far you get and maybe I'll have some time to look at it if it is still acting up.

 

Correct, now it doesn't seem to have any effect though.

Inde is a wonderful facility, you will love that track. I'll be at the dunes 2/20-23 so depending on when you arrive/depart I'll probably miss you.


Rob

 

Sounds like some sort of wiring connection problem, but guess you know that.
This may seem a silly point, but I've known others who have complained about this thinking it just operated on the door opening. re the interior light, you've tried the switch on the mid panel haven't you?

 

Too bad I'll miss you. Anyway, start with basics. Spark or fuel. Either put fuel pressure gauge on it or try some starter fluid in the intake and see if the car starts.

 

When the problem first appeared I depressed the valve on top of the filter and it barely dribbled. Guessing spark was non-existent as well considering the CEL was gone.


Yes, moving the switch on the interior light has no effect.


Thanks guys, keep the suggestions coming.

 

There's two plugs by the main ECM behind the passengers seat. They can be mixed up and mine were. The few times I drove it everything seemed ok. When I replaced the transmission at fast cars and they put the car on the sd they found the problem. These two plugs were reversed. They were the only two plugs I did not color code because I thought it was obvious at the time next time I will know better.

 

The permanent red light is more than likely not related. This is usually due to the on board battery within the alarm horn malfunctioning. If you do a search you will find that answer.

 

So your car ran (apparently) OK with these connectors reversed? What symptoms were you experiencing?

Still perplexed that unplugging the ECU fixed my issue the first few times.....

 

Rob,

The female ECU plug pins spread and leave visible light gaps so that when the male ECU pins slide in they are loosey goosey. Check for that with a magnifying glass. You may be shocked and how many open pins you have. Bend the female pins in the plug to get good connections. If that appears to be your problem then it is time to repin the plug. You either go it alone and source your own parts or buy SRI's Gold connector kit.

 

I guess that would fit with my timeline. No issues prior to me removing the connector, now I'm having trouble.

Tweaking the pins for an interference fit crossed my mind but I was worried about damaging the expensive ECU.

 

That is why you tweek the plug pins not the ECU male pins. You can replace the plug pins not the ECU pins.

 

Classic problem pin
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Sorry not back for a few days. Yes that's the weird part it seemed perfect. I did not think that was possible I wish I could remember what they told me was reversed. In my mind it should not have worked and Fast Cars said they did not think it should run either. They only caught it because the sd computer was not talking to the whole system. They check the wiring internally and one of the main techs had the idea that the plugs might be reversed. They checked that and everything was fine. I wish I could be more helpful but when I asked which plugs they said there is only 2 that could be reversed and they are behind the passengers seat.

 

Maybe follow FBB advice first I would hate for my solution to cause any more grief. And I had no symptoms except for my alarm light started staying on as well, but I replaced the alarm horn and that fixed it.

 

Have you double check your grounds?

A few years back I had a non start issue, and it turned out I had forgot to reattached the ground from the subframe to the gearbox.

 

Ernie, I will double check. Weird thing is that it was running great, would die, not start, CEL went out, disconnect/reconnect ECU, CEL back on, car starts runs fine, repeat. Now disconnecting/reconnecting ECU has no effect.

 

I'm no expert. I don't play one on TV. I didn't stay at a Holiday Inn Express. So keep that in mind when I say.....

Your immobilizer is dead.

 

On a 5.2 motronic you can immediately rule that out if the engine cranks. immobilizer in function will not allow engine to crank. I have not heard of an immobilizer that will let a car crank but prevent starting but that does not make it true. I could be wrong. The red ligth is only related to the alarm horn. You can remove it from the system and the immobilzer works the same way except no noise and the red dash light is always on. Red light always on is dead battery in the alarm noisemaker box. There is a fix for that or buy the corvette one.

 

Engine cranks after pressing button on fob. No fuel pressure at the schrader valve on the filter.

 

Then I would check the fuses for the fuel pumps.

 

Make 100% sure the wiring loom that passes through the firewall has the grommet installed correctly. I have seen services done where the grommet was not secured correctly, and the wiring harness gets cut by the metal. Also check to be sure that when withdrawing the loom from over the gas tank, that no wires were damaged. Lots of issues like the one your describing have been caused by this.

 

Absolutely...some of the issues are not immediate. I have seen it take months for problems to manifest.

 

Not true, on the 355, the engine will crank but not start if the fob is not pressed (immobilizer dis armed)

 

If you press the Fob to unlock the car, it will also disable the immobilizer. You have 120 seconds to start the car or it rearms