New Twin Turbo, Starting Issues, Help!!

[EM.TT]

Just bought a 91 TT and I'm having trouble getting it started. It has been sitting for a while but when I crank it over it will start and run rough for about a 2 or 3 seconds, then die. I don't have much of maintenance record for it, and only know that it was running fine, overheated, an then it sat for about a month. Almost all the warning lights on the dash come on, so I ran the diagnostics test on the ecu several times and got the 5 short, then 5 long blinks, so apparently the ecu thinks everything is good. It has a new wiring harness on the engine, new plugs, good oil, coolant is full, good battery, and I just tested the injectors and got one bad one. Any advice on where to start or what approach I should take on this mess?? Any help would be great! Thanks

[BigTDogg (MA)]

Welcome!

When you say it overheated, how hot and for how long? Your first step should be saving for new injectors. Your second step should be to do a compression check. Overheating can blow a head gasket, among other damages. Check your oil, if it appears milky, you have coolant in your oil, and a big problem on your hands.

[EM.TT]

Im not totally sure, it happened with the previous owner. But they made it sound like it wasn't for very long. I checked the oil, its full and is the right color and consistency, and smells like it should so hopefully not cracked heads? And coolant looks as it should as well. And with the injectors, I Ohm tested them all several times and got from 12.3 to 12.5 on 5 of them (these also have a purplish top so I'm assuming they were replaced somewhat recently), and then one thats all old and brown didn't even give me a reading so its pretty obvious that one isn't working! Should i replace them all anyways? And i'll do a compression test asap.

[BigTDogg (MA)]

They should all be the same color. Purple tops are 555cc/min, and IIRC, brown tops are the OEM TT 370cc/min.

The oil and coolant conditions are good signs. Usually a dead injector would give a code on the ECU for injector circuit, and the car would keep running and just idle rough.

[EM.TT]

Ok, thanks for the info! Do I need to put my plenum back on to do a compression test? That might be a dumb question lol.

[BigTDogg (MA)]

Ok, thanks for the info! Do I need to put my plenum back on to do a compression test? That might be a dumb question lol.

I don't see why you would. Except for the TPS to turn the engine over. I've never tried it.

[marty1mc]

It'll work. You only need the starter to function to test compression. The only thing I would be careful with is dirt. There is a ton of it around the plenum and you don't want to suck any into the motor. Tape off the plenum and vacuum all of the loose dirt off the top of the motor before you do it.

[EM.TT]

Ok so just did a compression test with the plenum out and the results are not good!

1-110
3-90
5-90

2-30
4-15
6-50

Im hoping that for some reason you cant test the compression with the plenum off, but either way these numbers all over the place. So this, to me, says engine pull, teardown, and rebuild. Or is it not worth it to pull the motor and just do it in the car??

[marty1mc]

Do a wet test and squirt a little oil in each cylinder. If it's rings, the compression will jump.

[robomatic12]

Also it may just be blown headgaskets/cracked heads from the overheat. That can cause compression loss, perhaps try a leak down test?