dboersma69

Hello everyone.. I just purchased a 1987 IROC-z 5.7 with 20K on it. It does have the typical brief blue smoke on start up from it's age and I plan on getting it fixed over the winter. My problem just started last week. At cold start it will start with barely a crank, but it seems to have a misfire at take off and sometime seems like a backfire. It also seems to have lost power. When I first brought it home this spring, I had to watch myself on the pedal because it would want to just rip the tires loose. Now even if I floor it, it won't even come close. Not that I rag on the car... I'm just trying to explain the power loss. I have changed the cap, rotor, plugs (bosch+4), wires(stock GM), and the coil. I had the injector service done and fuel filter as well. The injector service seemed to have helped at highway speeds but the power is just not there and it seems to be bogged down at takeoff. Now I'm a tpi novice and this is my first TPI. I've read through most of the threads and there seems to be similar problems but nothing exactly like mine.

All the plugs were very clean except the #8 which was slightly fouled... but the plugs were original and the new plugs are coming out clean after about 500 miles. The obd comes up with no codes. Car idles at 600 rpm smooth. On take off feels like it is chugging to get going. Runs great at highway speeds. Gets about 19-20 mph on the highway. Compression is fantastic and no problems in a leakdown. I see no arching in pitch black garage. I do here a gurgling sound from the tank (almost like boiling) after a 30 minute drive and lots of air preasure when I loosen the gas cap. There seems to be no vacuum leaks.

Any Ideas? I was going to take it into a local shop that specializes in TPI and late model corvettes to have them take a look but I though I might just check out all the owners out there first.

Viprklr

iTrader: (5)

Check your fuel pressure. Should be about 43psi with vacuum unhooked. Should also hold and not fall off quickly.
Ohm your injectors. Should be around 14ohms on all 8.
Set your TPS. The procedure can be found at the homepage under tech articles.
I would also toss those Bosch plugs. AC is the most popular. NGK and Autolites also work better than Bosch.

dboersma69

I wanted to let everyone know what the problem was... It seems the computer was bad and thought the engine temp was at 240 degrees all the time... this of course made the computer think it was running to lean and richened the mixture. That is the cause for the missing - too much fuel.

navyCM

iTrader: (3)

how did you figure that out...

dboersma69

I borrowed a snap on OBDI diagnotics from a friend and was paging through the computer readings on screen. 240 degrees jumped right out since the car had only been running for five minutes. Just to verify the temp, I used and infrared temp gun to check the surface temp all over the engine and came up with nothing over 170 degrees. I checked all the grounds and they were fine. I tested the temp sensor and it was fine. So I replaced the computer. The first one was from NAPA and fixed the problem for a few days... then I read somewhere that GM had issues with the solder connections in these ECU's and to only buy a GM reman ECU. I ended up getting one from the dealer and it cost me $100 more, but the problem has not returned since. The factory ECM was fine as well.