Help me out please! I just swapped in a 350HO and kept the TBI system (upgraded to 670 Holley, custom chip too). It all runs pretty well considering I did it myself, but, I don't have a high idle at start-up, so the engine runs kinda crappy and loads up/runs rich until it goes about a mile or so. I've changed out the coolant temp sensor and the air charge temp sensor in the air cleaner housing, but still no joy. Any one else had this problem? Anyone know what causes or controls the high idle circuit? This is new territory to me.
Also, is the 305 MAP sensor good enough for this engine or do I need to find one for a 350 and, if so, what year/make/model of car or truck would be best?



:hail:

 

Mike,

A MAP is a MAP is a MAP. There is no difference.

As for the idle RPM, the stock setup uses inputs from the CTS, IAT, and TPS to control the IAC, and thus, idle RPM. Since you have a custom PROM, I'd suspect there may have been an oversight in the cold start routine. Do you have a stock EPROM you can install to test that theory?

 

Vader,
Thanks. I'll contact the guy who did the prom and ask about the start-up routine. I still have the stock PROM and have tried it once with no noticeable difference. However, I had a bad MAP at the time, so that may have affected it.
Interesting about all MAPs being the same. I thought they might be different because I was in a salvage yard last week and was checking out the MAPs on a few different GM cars/trucks and noticed that although they look the same on the outside and the connectors looked similar, in fact, the connectors were not the same and not interchangeable. That got me to thinking, why would they all be different and not interchangeable for no reason? Why would they have different part numbers embossed on them and why can't you just go into the store and get any old MAP sensor? It seemed to me that there might be a difference. I'm old and perhaps have too much time on my hands...

Mike

 

Hawaii? Cold??? Where are you, anyway... above Kilauea? by the observatory on Haleakala?

If it runs really rich, then there's definitely some sort of cold start mode going on. Sounds like maybe it just needs some more idle RPM in the programming.

 

RB,
Well, cold is a rather relative thing. When its cold in Ohio, you just turn up the thermostat. Here, when it's 55 degrees at night outside, it's pretty much 55 degrees inside as well. All heat here is solar powered and pretty much limited to the daytime hours. But I suspect there's no pity to be had given that I live on a tropical island in the middle of the Pacific.
As for the high idle thing, my programmer is telling me TBIs are a handful to program in the start-up routine. I don't know what to believe. I do wish GMPP would come up with a chip for the 350HOs for those of us who like to use EFI rather than carburetors. There must be some OEM chip out there somewhere that comes close.

Mike

 

Well, gasoline and air work pretty much the same at any given temp, no matter how well- or ill-prepared the humans are, or how appealing to humans the surroundings are... When I lived in Southern California, right on the coast (very similar to Hawaii except about 5-8° cooler, and far enough north to have noticeable seasons), it was about the same way; no insulation in houses, heating systems that barely worked, etc.

Anyway, enough yanking on you. Call whoever did your chip, and tell them exactly what it's doing, it should be pretty easy for them to take care of. Every motor is more or less a "handful" to do the cold-start routine, TBI probably is worse than port injection though since it shares the disadvantages of a carb (wet flow) in that regard, that also make carbs notoriously hard to get perfect.

GM is never going to come out with a chip like that. Every motor is different, once it's been "modified"; there's no way to manufacture a one-size-fits-all for totally custom applications.

 

As for the MAP sensors, there were connector changes corporate wide across the years. The early '80s types were larger and more cumbersome. The WeatherPak early versions were slightly smaller and used a relatively standard pin spacing for all connectors, with different keyings for specific applications. The later WeathPaks were even more trim, made for smaller wire, and had a tighter pin concentration with similar keying arrangements. You may also have been comparing a BARO sensor to a MAP sensor. While they are essentially the same in function, the output ranges at a given pressure are substantially different, and the connectors were probably intentionally changed to prevent inadvertent mis-application.

 

Vader,
Thanks for explaining it a little better. I didn't know both Baro sensors and MAP sensors were used. They all look the same on the outside. So anyway, I'll rest easier knowing at least one piece of the engine-computer relationship is fine as it is.

later,
Mike

 

RB,
Whatever, Hawaii is definitely nicer in the winter than Ohio. I've got plenty of blankets, but I threw all my snow shovels away when we left Maryland.
The last correspondence I had with the programmer he suggested getting a laptop and a connector and downloading the readings from the engine as I drive along. I can probably borrow a computer, but where do I get a connector and what software do I need to take the readings and store them?
You're right, GM is unlikely as snow in Waikiki to make a PROM for the 350HO, but it's a good pipe-dream. They spend a lot of time in the owner's manual describing how the mechanical advance should be set and what vacuum can to use on the distributor, so with all that engineering talent, it shouldn't be a problem to put together some kind of PROM that provides what I need.

later,
Mike