1998 C70 misfire

[anthony23]

Hello, I'm pretty sure I have bought the C70 from Hell. I am attempting to fix this car so she can shine in her glory, but it's really starting to get hard to keep going. I bought this car last January and sadly have only been really driving it since October. She had 130,000 miles, auto, coupe, 2.3hpt, bought knowing it had an oil leak of some kind and some issues. So with that I am asking for some help in which direction I should be looking next to fix my misfire issue. I currently have the codes p0300, p0302 and p0305. The following is the expensive list of EVERYTHING I have replaced in the last year.

New head/head gasket (old one was warped into the shape of a banana)
New Timing belt and water pump
New pcv system (bought from ipd)
New import direct cap/rotor
New import direct wires
New Champion double plt plugs ( I just ordered Bosch copper plus plugs, they will be in tomorrow)
New coil pack
New fuel pump
New fuel filter
Injectors Ohm cold 16.4-16.6 and warm 15.5
I have a new/used set of injectors and fuel rail but they are not yet installed
Tightened down the camshaft position sensor reluctor which was found to be loose yesterday

We took some live data on Sunday and when the cel flashes and "misfires" (I have yet to actually feel the car misfire) the fuel trim drops down to nothing and flat lines for a good 45 secs to a min. However, when this happens the car appears to run fine, no loss in rpm, speed, nothing. Now Sunday night leaving my mother in laws house the car struggled to start. This is a first. I turned the key and the starter turned over but the engine would not catch. Finally I got it to catch and it would die. Tried again, it caught and then I gave the car gas and she stayed running. Went to dinner, started fine when I left. Now coming home I was on the interstate I felt her buck pretty hard, rpms and speed were dropping and when I gave her gas I got nothing. Pulled over and the car instantly died. I attempted to start it again and it absolutely refused. Towed her home and Monday Fiance went out and turned the key and she started right up. Heard a scrapping sound and that's when he found that the reluctor was loose and there was a crack in the hose that comes off the very top of the turbo approx 3/4inch dia hose and goes under the intake manifold into the darkness. Reluctor was tightened and hose piece was replaced, car was driven, mile down the road "misfired" still.

I honestly am at a loss with this car and I feel like were never going to find the actual problem here. I've asked 3 different mechanics ( I deliver parts so have plenty of access to different ones) and they all give me different answers and then of course tell me to bring them the car. Problem is I don't have money to pay a mechanic anymore. My fiance and I are pretty good at fixing cars as well but this car is too much of a puzzle. She's fun as all hell to drive and I love boost and she does too but apparently just cruising down the road is too much to ask.

[JDS60R]

Your already looking at fuel trims so you are on your way.

Start with the right plugs ( you are getting them today) and then inspect the cam sensor for damage from being loose. If it nicked the winding replace it.

While you have the plugs out get a compression reading and report back with the numbers.
If you have good compression and we know we are sparking correctly ( remember these cars are known to have firing issues when the original Bougicord wires are not used which doesn't make logical sense but does seem to be an issue) then we will look at fuel/air having a short and log term trim below 5% is our goal so if its not we can look at the MAF and injectors.

[anthony23]

OK, I'll be changing plugs, but as far as a compression test goes we had one done by our local euro specialist and he didn't give me exact numbers but did say that all was well and that compression numbers were excellent. Now when you mentioned fuel trim staying up at 5% that makes me wonder because the fuel trim varies between -5.5 and up to +8% it never really seems to stay steady how significant is this?

[JDS60R]

+/- 5% is fine. Short term will bounce around. Remember you are adding them. So a long term at +5 and a short term at -5 is actually 0 at that moment.

You should do a compression test now. The only compression test that counts is the one when the problem exists. Having it done previously provides no diagnostic value. As a mechanic I can not say it can't be compression as I tested it 3 months ago. We have to do it now, as the possibility exists because of a burnt valve or a stuck ring. A vacuum check would help as well. If low compression or weak or shaky vacuum is found now make sure to do a leakdown test as well.

If you are unable to do these diagnostic tests then go to a pro. Local auto parts rent these testers for free( deposit returned when undamaged tester is returned).

If you want to find the problem you have to do the tests. Otherwise you are just guessing and that gets expensive.