Greetings Corvette forum my names Gunner and ive recently picked up a 1998 c5 a4 for a steal! About 2 months ago I drove 6 hours to grab a c5 that "needed a bcm" and bought it for $1500, yes you read that right. Interior was missing everything but the seats and dash and only had 68,521 on the odometer. Previous owner was unable to figure out the LMC5 install and was the reason for the "bad bcm" comment and the sale. In the first month ive replaced quite a bit: New fuel pumps L&R, new crossover hose, full -6an fuel lines from rail to tanks, shifter cable, most of the interior, wiper motor, LMC5, vats bypass, Oil sensor, crank sensor, catch can and intake manifold gaskets. For the last month and a half the car has been a great weekend driver with the occasional "pull key wait 10 seconds" I assume its from the 7 year old battery (since changed). Recently the car has become a gremlin! My issue first stated with a very odd start, car cranks and sputters like its got no fuel pressure but eventually starts up. She will then surge and die for about a min having to restart the car 2-3 times before she smooths out. After that it will run and drive 100% with 0 codes. Fuel pressure at the rail is 60psi and will hold for a very long time. Recently I finally got my first code, high map sensor voltage. Removed and replaced with OE, checked harness behind heads (seen on here that the metal injector harness clip can dig into a cut wires) and it looks great no corrosion or busted wires. After hooking up the battery I noticed a new message "Service Column Lock" and hooked my scanner up to see what was going on and once again no codes in powertrain or BCM. Battery read 11.3 and Ive seen on here It NEEDs 12+ or the bcm gets an attitude. Charged the battery on a trickle charge all night, read 12.6 after it sat for a few min off the charger. After hooking up the battery car wont stay running. She will crank like normal but sounds like it has no fuel, chugs very hard 200-500rpm for about 5 seconds then dies. Car has 3/4 tank of GOOD gas, 12+ volts on batt, 12v on pump then 0v when she dies. I removed my resistor and went back to the OEM vats/key system with my OEM key (my spares are the wrong vats type, non issue with the resistor installed. ). Now the car wont crank with or without vats. I can hear my relays clicking in the bcm fuse area and using a relay tester they show good but again no codes. When trying to crank all my gauges drop to nothing like Im getting ready to pull the key and come alive once I stop trying to crank. I double checked EVERTHING I touched in the engine bay and in the cab to verify and I see nothing wrong.

This car has a issue with the actual gear shift (not the cable that's new) the shifter has always gotten stuck at 75% into park and caused the cable to break at the trans. The shifter shows the red indicator about 75% in the "P" but the key can be removed from the ignition so ive tolerated it. Yes im stupid but ive been removing the gearshift and actuating the cable by hand and have been driving fine like that. I haven't purchased a new gear shift because this purchase also included most of a manual swap, these issues have discouraged me from the swap as id like to make sure the car is 100% before I take on that massive task. I also really hate wasting time/money swapping parts when I dont know if its gonna fix the issue.

If anyone has any ideas or suggestions please let me know, Id also be happy to provide voltages and ground references in the car to aid in diag. This might of been a long and confusing read (im sorry) but id be happy to clarify if asked!

 

Most likely your Park/Neutral safety switch is not allowing the car to crank over, the start voltage originates at the Ignition switch, makes it's way to the Park/Neutral switch and then on to the TDR. Is your TDR clicking on when you turn the key to the start position of the Ignition switch?

 

Yes I can hear it click each time I try and crank the car.

 

The next step is to insure you have 12v on the violet wire of the TDR, this is the wire that connects to the starter solenoid. There should be 12v on that wire when you hold the key in the start position.

 

Purple! Violet is for resistors

 

Just because you can charge a 7 year old battery to 12.66 volts doesn’t mean it’s good…I wouldn’t even bother to load test…just replace it !!…and you shouldn’t be testing anything below 12.45.

 

BTW if you had a P0108 “high voltage” it’s usually not a MAP sensor issue but a wiring one…did you check the MAP sensor wiring before changing it ??…trouble codes are not part numbers….what does your MAP sensor (BARO) read key on engine off ??…should be 101 kPa at sea level or 14.7 psi or 29.9 inches Hg…a skewed MAP will cause the engine not to run…saw this a few months ago on here or the C6 Forum.

 

Work go in the way and pushed my diag back. However checking my voltage at my tdr relay and they are all good, all engine and bcm cover fuses are good with no black marks/corrosion. ALL relays have been tested externally and showed good, replaced em to be 100%. Ordered a new shifter and a new interlock shift cable as both where questionable. After replacing them the car would crank again but give the same fuel issue. I removed my ignition switch tore it down and cleaned the life out of it, almost every terminal and contact was black with corrosion on it and was cleaned with some fine grit sandpaper. Map sensor reads correctly (4.91v 14.7psi) with Key On Engine Off and wires where checked BEFORE I replaced it as ive seen some less than desirable butt connectors on this car already. Battery was also replaced after the attempted charge, red top is in the car and reads a healthy 12.3/12.4 earlier today I decided to check over everything again but this time with a second set of eyes and hands. Had my lady key on the car and crank and fuel pressure its now a concern. 58psi on key on BUT once the car cranks and runs for 2 seconds the pressure drops to around 20psi and the car stalls out (couldn't see this before as the car would die before I got out of it to check pressures) . As i stated before almost every part of the fuel system has been replaced leading up to the motor, I now suspect my pump or filter to be clogged or bad. When the fuel pump relay is removed and a jumper wire installed the pump only stays on for about 15 seconds when I key on the car, it builds up to about 55-60psi then goes quiet and kicks back on every few seconds with a pulse keeping pressure the same. When removing my fuel feed line from the rail and putting it in a bucket and using my scanner to turn the pump on the fuel comes out at varying speeds, sometimes it its a constant flow and other times it sprays out. This has further convinced me of a pump/filter issue. Before draining 3/4 of a tank of gas is their anything else I should check before removing the pump and replacing it again?

 

So right now you have a crank no start ??...if pressure drops after 2 seconds while cranking this may be a lack of a crank sensor input...do you see any RPM or a crank sensor "counts" or "RPM" data PID on your scan tool ??...also do you have a "fuel enable" data PID and if so I would look at those during cranking....with terminals 30 and 87 jumped at the fuel pump relay with the key ON the pump should run continuously...I would do a voltage drop test on the fuel pump wiring to rule out and high resistance on the positive or negative side of the pump circuit....video below...you can voltage drop even if the pump runs for a few seconds and as long as there is current flow.

 

You mentioned replacing fuel lines from rail to tank, did you also replace fuel filter at that time? I would check your fuel filter before draing and pulling fuel pump.

 

Upon posing this I was at a no crank no start. After replacing the shifter and intermediate cable I was able to crank again. The car cranks and starts beefily before it dies out. Currently im figuring out a fuel pressure issue, car has and holds pressure but looses it after cranking and running for 2-3 seconds. Scanner shows rpm as does my dash. If I cycle the key 5 or more times I can get the car started and run with my foot on the gas at 2k ish rpm for maybe 5ish seconds then it just drops to 700rpm and dies out, pressing the gas pedal has no effect once the rpm drops. My scanner has no indication that fuel shouldn't be flowing ive got 3 sections that talk about a lockout/shutoff "engine protection", "Fuel cutout" and "Security lockout/immo" which are all false, the security lockout will be true for the first few seconds of turning the key to run then goes to false and will stay like that till I cycle the key to off then back on. After watching the linked video I went outside and tested the pump, on both positive and negative I had no higher that 0.220 drop on either side. During the test it did the same thing its been doing, pump will run till pressure is reached then get quiet and only come on every few seconds voltage stays the same 12.5/12.4

 

Yes it was changed, not oem though its just a rock auto one.