Need some help with 88 TBI Chevy truck

[TurboBuickSix]

I swapped an 85 305 from a monte into my 88 k-5 Blaser.It previously had the 5.7 liter TBI.I used the 305 because it was all I had at the time and healthy.I kept all of the electronics and put the 88 tbi intake on the 85 heads.The EGR don't work because the ports are different between the 2 sets of heads.Well the problem is terrible part throttle knock due to the egr not working so I really need a guy that is capable of burning me a chip for this truck.The knock and off idle stumble is really bad, but when it is cold (closed loop?) it runs strong and responsive and no knock but as soon as it warms up(open loop) knock city and feels real lazy and underpowered.Can someone,maybe some who has done this swap before,guide me to a chip burner/maker before I loose a piston in this thing.thanks

 

[myclone]

FWIW... The 305 and 350 have diff injectors (350s are bigger) and the PROM is diff between the two. You might throw a GM prom that is for your year truck but for a 305. You can get em from the dealer for ~$25 (maybe less... cant recall right off).

This may help your part throttle knock some as Im sure the timing/fueling curve calibrations are diff for the smaller engine. Prolly wont cure it completely but may help keep you from holing a piston or hammering the rod bearings out of it. For a little over 20 bucks it might be worth it

BTW. Warmed up is closed loop and a cold engine is the opposite.

 

[REEDOG]

Try these guys, lot's of experience with TBI. http://www.turbocity.com/TBIPowerMain.htm

 

[myclone]

Ummm.... The chips are physically the same but the cal is diff for all three engines. The TBs themselves are physically the the same but the the 350 uses a slightly larger injector according to some research Ive done and the ppl Ive talked to on gmfullsize.com (not 100% sure that addy is right).

IMO you could swap chips and/or TBs between all three engines and get the engine to run.

Then again whadda I know.

 

[TurboBuickSix]

I forgot to mention,if I got WOT with it there is no knock at all,this is strictly a part throttle thing.Very low rpm,right when it would expect egr to be present.
I am pretty sure a chip would fix it but was'nt sure about the injector size being the same or not.If it is the same then it wold just be a regular chip cal but I was thinking it may be different and would the need to get a chip for the 350 inj on the 305.It makes sense that it would be the same injector because the displacements are not that far apart IMO.So I should be able to just get a high performance chip for a 88 305 TBI and be good hopefully.Please correct me if I'm wrong on anything here.Thanks for the tips.

I'm going to borrow my buddies turbolink and see what that tells me about the knock sensor and timing etc etc.

 

[myclone]

At WOT you go into PE mode which is way richer than at cruise due to the ecm going to a diff fuel/spark table(s). Thats why the detonation goes away at anything other than light throttle.

You could try retarding base timing a few degrees (which didnt work for me when I was trying to get around a blocked EGR back in the day).

Lower the coolant temp with a 180 deg t stat (prolly slightly kill off some MPG too as your now running in a lower temp fueling table).

About the only way to get rid of the detonation is to drown the detonation with fuel (cools combustion chamber), retard timing (which in my experience killed power because it had to be retarded so far), cool the combustion chamber from the outside with the coolant with a lower t stat, or have a custom chip burned. Last but not least is to get some EGR into the comb chamber which isnt an option for you right now.

FWIW dept..

4.3 uses 45lb/hr injectors
5.0 uses 50lb/hr injectors
5.7 uses 61lb/hr injectors

5.0, 5.7, and full sized PUs 4.3s use the extact same throttle body housing. The s truck throttle bodies are rotated 180 deg (on the two Ive tinkered with) from the full sized so the fuel line fittings actually face the front of the truck. Full sized TBs face the fire wall.

2.8v6 trucks use the smallest of all the V engine TBIs, and 454s use the largest.

There are usually several diff proms that were released from the factory for a given year truck in just ONE engine size due to updates, bug fixes, etc during the model year. You will find if you look at the bin files for the 4.3, 305, and 350 they do indeed differ in the timing tables and fueling tables among others.

 

[TurboBuickSix]

Seems like the easiest way out here is the custom chip which I don't mind,I just need a source.I wonder why the extra 350 injector size compared to the one the 305 calls for won't help supply enough extra fuel to kill the detonation? It does not seem to run rich but I am gonna call my buddy up today and see if we can record some turbolink files to get a better idea if it is lean or timing or both.Someone also suggested that until I get a chip to put a resistor in place of the cooling sensor to make the ecm think it is cold and stay in "closed " loop? Or is this bad?

(thanks,and I promise I won't mix those loops up again )

 

[WFO]

Originally posted by sunnygn
350's,305's,and 4.3's are all the same injector,chip,throttle body,and ecm.

very interesting.i'm reseaching doing a gm tbi swap onto my carbed dodge ramcharger and i've been getting the same conflicting reports.i'd like to just find a 454 setup and be done with it as i know it's the biggest.

anyone know who can burn a custom chip for tbi?i wonder if steve yaklin could burn me an open loop "tbi maxeffort".that would kick ass.

good thread fellas.

later,sean

 

[myclone]

There is quite a bit of info to be found by using the search function on the gm ecm mailing list link below and I had a BUNCH of TBI stuff/info saved in my favorites folder but my aol crashed a week ago and I lost all of them (gotta love having to reload aol )

http://www.diy-efi.org/gmecm/

Heres a little more info on TBI injectors from gm ecm.org.

http://www.diy-efi.org/gmecm/component_info/tbi_injectors.html

If you look around on these sites and their related links then it may help clear up some of the confusion on the TBI applications.

HTH