This is not related to our cars, but since so little posting goes on here, I thought you might entertain a question I'm having trouble with. Mods, Please delete if this is frowned upon or not permitted.
Vehicle: 89 Silverado
Engine: 5.0L / 305 (formerly 5.7L 350)
Fuel pump: Stock
ECM: Stock, still programmed for 5.7
TBI: Stock from 5.7
Issue: After I replaced the engine with a used long block a couple of years ago, reusing all accessories including the TBI, it has never run perfectly. Super reliable, smooth idle but bogs at certain RPMs.
I've slowly done things to try and improve it. New plugs, wires, knock sensors, 02 sensors, EGR, trying variation on the timing, rebuilding the TBI and regulator.
In recent reading, I'm realizing the stock '350' injectors are likely 51lb/hr and the 305 injectors are likely 45lb/hr. My assumption is the ECM still 'thinks' I have a 350, causing too much fuel delivery and perhaps that's my problem.
I've ordered a pair of remanufactured TBI injectors rated @ 45lb/hr for a 1989 305 truck. The parts arrived yesterday.
Before I install them, I wanted some input. I have no logs, no AFR data and no way to gather it, so I'm shooting in the dark somewhat.
those old vehicle ECM's still run on the basic principles the newer ones do.
i'm sure it runs on alpha-n or speed density.
at idle, low throttle, and cruise, it has probably learned the trims for what will make in run halfway decent. at higher rpms or heavy throttle i would imagine it would revert to whatever open-loop power-enrich mode those computers used back then. so, just dump the preprogrammed amount of feul.
i think LTFT principles were similar under WOT back then. adds positive feul, but does not subtract at WOT.
i dunno, i say try the injector swap and see how it does. reset the computer and swap the TBI injectors.
make sure all your sensors are up to par, as well. those older ECM's that don't rely on MAF sensors are very reliant on the TPS, MAP, and ECT sensors to run right.
The real enemy of truth is not ignorance, doubt, or even disbelief. It is false knowledge.
Cookmeup - Swapping ECM would probably be more expensive. I only paid $46 total for replacement injectors. I'd also be worried about other things like RE ratio and shift points. At least right now, I have the factory ECM paired with the original chassis.
Humble - I was able to pick the engine I swapped in out of a wrecked '90 Silverado with TBI, and they pulled it for me and delivered it. Only after I had it almost ready to drop in, did notice it was stamped as a 305, but I was too far along.
NotHubert - All good points. I've checked the TPS before and have some faith in the rest of the sensors.
>> i dunno, i say try the injector swap and see how it does. reset the computer and swap the TBI injectors.
That's my gameplan tomorrow. Wish me luck. Any idea of the 'relearn' time on something this old?
So, he'd have to swap them anyway, i would imagine.
The ECM for that year model c1500 should also be the same for each engine.
Not sure there are still places that will make a custom PROM for you, but you may want to go that route. Or find a PROM from a silverado in the yard with the 5.0 engine/same ECM... provided it isn't fried.
The AutoGuide.com network consists of the largest network of enthusiast-owned enthusiast-operated automotive communities.
AutoGuide.com provides the latest car reviews, auto show coverage, new car prices, and automotive news. The AutoGuide network operates more than 100 automotive forums where our users consult peers for shopping information and advice, and share opinions as a community.