85 Monte Carlo SS build

[JPack]

Is the dfi back on the car?

[firebird_1995]

So here's the rundown going back to the very first startup.....
My original intentions were to start the engine up with stock injectors and without the supercharger to break the engine in before pouring the coal to it. That didn't happen. So when I got it ready I fired it up with 60# injectors and the supercharger attached and found it would start and immediately die. It took a lot of troubleshooting to finally find out the msd opti was the culprit. What was happening was as soon as the key was released, the system voltage would spike due to the starter being dropped from the load. Evidently msd optis don't bode well with voltage spikes and it caused the accel dfi to lose a crank signal and stop firing. I've since learned that the accel dfi uses a 12v signal on the low resolution side of the optical sensor where the factory pcm uses 5v. I was told this is normal and "nobody else has had a problem like that". I think that's why most guys running accel dfi have problems with msd optis but I can't prove it. Anyways I changed the opti out with a known good gm unit and it fired up and ran, but it now would backfire through the exhaust. So the troubleshooting began again. I thought maybe my known good opti was bad so i replaced it, no luck. Then i removed the supercharger and 60# injectors in lieu of stock equipment, then swapped icm/coil, spark plugs, wires, various sensors, readjusted valves, checked fuel pressure, tried numerous tunes and eventually removed the dfi and installed a stock pcm. At this point the engine had about 10 minutes of run time and about 500 startups on it and the oil had been changed 3 times due to fuel contamination. Plugs had to be cleaned every 20 starts or so because they were fuel fouled. This lead to the compression test. The only compression tester I had was an old Napa balkamp tester. It had a flexible hose but you have to hold it in the spark plug hole. Hard to do while cranking. So I went to O'Reillys and borrowed theirs. When I ran the compression test I found ~75# on all cylinders. Added oil to the cylinder and the pressure would rise to around 125. While troubleshooting the issue where it would start then stall, every time the key was turned those big injectors were dumping fuel in and washed out the rings. So I rering it. Still backfires. I grab the O'Reillys tester and its back to 75# pounds. At this point I can't believe that ALL cylinders were at 75# both times. I have my wife come out and help me as I put the Napa tester in and it reads 125-135. I mix and match gauges and hoses and come to the conclusion that the O'Reillys tester has a leak in the hose. Now, I can't deny that fuel was finding its way past the rings the first time, so it probably needed new rings anyways, but I almost junked the whole project because I thought the new rings didn't take. So now that I knew the compression wasn't an issue, and the backfire persisted, I tried a few more last ditch effort things, readjusted valves, changed tunes, nothing. So this morning I decide to try a few suggestions. Popo suggested trying a hotter heat range plug and featherburner suggested a fuel drier and fresh gas. I had been swapping betweeen autolite 103's and a previously used set of ac delco tr44s. I bought a set of autolite 106's, a new coil, a bottle of heet, and 5 gallons of 87. I changed the plugs and coil, added the heet and fuel. Guess what, no backfire. I swapped the new coil out with my old one just to see if that was the culprit but there was still no backfire. So my thought are, while the autolite 103's were definitely too cold, the ac delco tr44s should not have been and I tried both. The entire fuel system was new from the tank to the injectors. During troubleshooting with the 60# injectors, I had put 5 gallons of 93 octane fuel in on three separate occasions. It is very humid here and the temperature spikes from hot to cold all the time so i guess it could have happened like that or maybe i got a bad batch the first time. So I don't know when or how I got water in the fuel, but I'm leaning towards that being the culprit of all this heartache.


The end!

[firebird_1995]

Is the dfi back on the car?

Yes. I'm using a tune George Landis wrote for a few boosted lt1 cars hes done in the past.

[firebird_1995]

I will be there the 14th and are shooting for TNT night Wednesday the 17th if you want to come out, in whatever vehicle. Gonna try to get the Nova down in the 12.70's.

That sounds good man, can't remember if you did the spring in the elbow yet or not??

I have a section i cut out of an aluminum 90 that keeps it from collapsing.

I'm hoping I'll be working closer to home by then. I've been saying I'm going to meet you guys out there but it just hasn't happened yet.

[JCzNova]

I have a section i cut out of an aluminum 90 that keeps it from collapsing.

I'm hoping I'll be working closer to home by then. I've been saying I'm going to meet you guys out there but it just hasn't happened yet.

It's awesome that something is finally going right for you on this swap. Hope you can make it out, as this is the last time I will be in town, and the last testing I will have prior to the Shootout.

[firebird_1995]

Thanks! I needed to catch a break.
Well I'm always looking for reasons to get out of work, I hate driving 4.5-5 hours a day and we need to tnt my dads car anyway. Sounds like a plan!

[popo8]

So happy things are coming round for u... Def do t wanna jinx u...so pleaseeeee keep us posted!

Co-Owner/Admin @ LTXtech.com

[firebird_1995]

I just can't believe it would be something so simple like plugs or fuel. Maybe it was a combination of both. Either way, that problem is solved. But........ I think I may have a potentially fatal design flaw with this setup.
With the throttle body moved from the front of the intake to the inlet of the blower, I've extended the distance under vacuum from a little to a lot. While this by itself isn't an issue, should a coupling blow off under boost the engine would be free to suck in all the air it wishes to consume. My concern is, if this were to happen the map sensor SHOULD sense the drop in pressure and adjust the AFR accordingly and keep the engine from going lean but with no throttle blades to shut the air off, the engine would runaway. I guess that's what rev limiters are for but depending on when and where it happens that could be bad. Next design, the throttle body is going back to stock location.

[MeanTA]

Glad to hear the dfi was not Tue issue. and car working out for you!

[firebird_1995]

Glad to hear the dfi was not Tue issue. and car working out for you!

Thanks. I wouldn't have told you if the dfi was at fault anyways :p


^ this guy offered to help pay for any repair needed to the dfi, even though he never ran it. :thumbup: