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Anyone have a .bin file for a 1990 TPI L98? Covette roller motor with aluminum heads...
I recently transplanted a 90' TPI long block in my 91" Blazer, and I'm running the Blazer factory TBI along with the factory ECM on this engine.
I'm having some weird throttle transition issues on light to moderate accel. Some hesitation, a stumble now and then and every once in a while a pop thru the intake.
No codes, fuel pressure has been adjusted throughout the spectrum and it either gives me a good idle and shitty wot or vise versa.
Base timing for the roller is 6* vs the TBI flat tappet base timing of 0* with esc disconnected. I am running a makeshift EGR system off of one of my exhaust manifolds as the Vette motor did not have a EGR provision in the heads like the cast iron heads do. Seems to work ok.
I ran a quick log the other day and my BLM was fat around 117 @ idle and went lean up to 147 on acceleration. Not sure if I'm getting too much egr at part throttle or if my ignition curve is wack. I'm pretty sure the fact that the roller cam has a different profile than my factory flat tappet had, that my ignition map is gonna need to be addressed at some point.
Looking for someone that can look over a log file and help me out with a possible tune correction. I can get a burner and the memcal base from Moates for a burnable chip for my ECU. I can log data and interpret it, problem is I'm not to keen on where to make the adjustments in the ECU file structure though.
If so, how did you get the EGR to bolt onto it? I hand-made an adapter for mine. The gasket surface, exhaust passages, and bolt pattern are different than the TBI-style EGR valve.
I see an exhaust-gas tube from the #2 exhaust manifold port, going up in front of the valve cover. I don't see how it connects to the EGR valve, though.
You will need to ditch those 55 lb/hr units unless you run around 30 psi fuel pressure. 55 lb/hr is a 305 injector. It is bogging and popping because it is starving for fuel. You could plumb an external regulator with a vacuum refernce to lower the idle fuel pressure.
Camshaft does not make that much difference to the timing curve, but the head design makes a big difference. Base timing will need to be around 10-12° BTDC with those heads.
So I used the GM Performance Dual Plane intake. The intake has a provision for a "Hot" choke pull off or what they call
a thermal bi-metal spring choke. I plumbed the exhaust line into the little square choke port. This port is tied into the EGR exhaust port on the internal EGR runners built into the manifold. Exhaust goes into the choke port and supplies exhaust to the EGR port, because they are both linked internally, I now have EGR gas at the EGR valve. You can get a fireplace gas supply line (stainless steel) at Lowes. I used a 24" line and it worked perfect. I also had to make a special adapter plate to go on the adapter to adapt the EGR further. It still binds up on the IAC connector. Freakin mess really. It does work, if that's any consolation.
On another note, I know I'm gonna catch hell from the " TBI is soooooo easy to tune" crowd but I have decided to cave man this motor and go with an Accel HEI dist along with a Edelbrock AVS2 650 with vacuum secondaries. I've had electrical issues with this TBI from day one. Rando stalls, erratic idles, no A/C idle up, never a code to work with. Sometimes it runs great, sometimes I'm left trying to limp it home. I've had the dash apart looking for chaffed wiring, even replaced the ECM. I'm tired of f*ckin with it to be honest.
I've done enough research and have enough experience to know a properly tuned carb along with a properly curved dist using wideband will perform just as well as any rudimentary fuel injection system.
1. Yes, that's the same manifold I'm using. Came on most of the "ZZ" series performance crate engines, and was also sold as a separate piece.
2. Getting the EGR valve away from the IAC takes an adapter from Edelbrock, or similar. (There is--or was--an off-brand version of this.) Relocates the EGR farther to the rear, mostly out of the way of the IAC. https://www.summitracing.com/parts/edl-1476
3. But that adapter is still not correct for the EGR on a TBI. That's why I had to make an adapter plate to go onto the Eddy-style adapter.
I bet your adapter is similar.
4. Cramming a carb on this engine is a mistake. Stop looking for "codes", start looking for sensor and output data on the computer's data stream. Verify fuel pressure, then connect a real scan tool. Find out what the ECM is trying to tell you.
5. Random stalling can be the magnet assembly built-into the distributor mainshaft. They're infamous for cracking, leading to poor/weak signal to the ignition module.
Note crack just below Copyright symbol. Extends through rivet all the way to the outside of the magnet.
01-26-2022, 01:51 PM
