What a way to start things off, the folks over at Colorado K5 suggested that I make a trip over here. And since a lot of them admit that y’all are the experts on TBI modifications, here I am. My problems started when I replaced the stock TBI on my stock ’88 K5 Blazer that has a 350/700R4 with a 670 CFM Holley replacement TBI. Everything went on like it is supposed to and after playing around with it some I have a couple of problems that won’t go away even after changing out a bad O2 sensor and a vacuum line to the MAP sensor. Here are the ALDL readings at idle in neutral:

Stinking rich idle.

Popping in exhaust during initial warm up (cold-start) along with light black smoke (mixture waaaay to rich).

Hesitation when throttle is quickly opened. (either in neutral or gear)


Win ALDL data:

IAC readings: 40 no change at idle.
O2 readings: 0.03 to 0.60v bouncing all over the place.
RPM: surging from 700 to 800.
TPS: steady at .50v
Temp: 185 degrees

Flag data:

Idle/cool (at 185 degrees?)
DRP occurred
Closed loop mode
Rich flag
BLM enable

BUT when I put it into gear, big difference! The 02 droppes and stays steady, rpm's steady and the IAC startes doing its thing! I know Holley replacement TBIs have a reputation for running rich at idle but I think mine is too rich, especially during the cold-start cycle. This dang thing is driving me crazy, does anybody have any ideas? TIA

 

What are your other mods. If you have the stock intake you are going to have tranistion problems with incoming air. Also, what injectors are you using. If you motor is stock i would use the stock injectors with the Holley unit. When you change injectors you really need to burn a new chip for them to work right.

 

Right now everything is stock except for the exhaust which consists of the stock manifolds and Y pipe, this feeds into a 3" in & out hi-flo cat then into a 3" in and twin 2 1/4" outlet turbo style muffler with the pipes exiting under the rear bumper.

The injectors are the ones that came with the Holley.

BTW, I read all of the posts concerning the lack of added hp that the Holley TBI makes, and my 'ol 350 must be different or the factory TBI was worthless because the butt dyno registered a major improvement, except for these last two headaches.

 

I think you need to put the stock inejctors back on. Use the unit but switch out the pods. See what that does for your rich condition at idle. Have your tried to lower the fuel pressure a bit?

 

According to this post:

https://www.thirdgen.org/techbb2/sho...ghlight=Holley


...The newest models of the Holley replacent TBI's have different injectors than the older ones had. They went to a Delphi injector ...

...The GM injector pod will not fit the Holley TBI housing, and all Holley injectors are proprietary...

...The 502-6 (GM stock replacement Holley TBI) has 65pph injectors, and a adjustable pressure regulator up to 21psi.


I've backed out the pressure regulator down to about 5 psi and it made no difference. I've been trying to iron this out for a couple of weeks now.

 

Yea I was afraid of that. Well the injectors you are using are still to much for your mods. A custom tune will be the only way to remedy your situation.

 

Arggggggggggg, I was afraid of that, and I don't think there is anybody in this area (sw va) that does it. Is that also causing the very rich cold-start cycle?

 

Yup most likely.

You could data log and send your stuff to a reputable burner. They should be able to dial it in since you are basically stock.

 

Have you tried contacting Holley to see what they have to say?

Steve

 

I've called Holley about a dozen times and finally caught thier resident TBI "expert". He suggested that I back off the fuel pressure until it got better...ha! I did find out that the built in regulator will decrease the fuel pressure down to about 5 psi though. I called him back (a longer wait than usual) and he's stumped. He said that that unit is a direct replacement and that it should work with no problems and that eveything is designed to be the same as the stock unit, so the only thing that should need adjustment is the TPS setting.

Since I'm stumped and grasping at any ideas, could the EGR possibally cause this or maybe the MAP sensor? Please remember this is my first venture in tuning any FI motor. I grew up wrenching on those land yachts of the late 60's and 70's.

 

the base pulse width in eprom made need to be adjusted. the ecu think the small injectors are in place when in fact they are not. how is fuel mileage with this unit. i bet not too good. dropping fuel pressure should help a lot but 5-6 lbs seems very low. GM is desiged to work at 12 lbs for older TBI. holley is calibrated at higher pressures with smaller injectors. apples/oranges. tuning is your answer.

 

Thanks Ronny, after thinking about the pulse width, that sounds like the problem. :hail: The mileage is about the same as with the old TBI, which is about 10mpg. My problem now is to find somebody that can burn a chip. I'm not sure if it's against the rules to ask, but does anybody know of a reputable burner?

 

past week or so a list was started with comments. see this forum..