I have an 86 suburban that I converted to TPI back in 02, mainly because of the crappy idle, and performance of the Computer controlled Q-Jet. The engine was, at the time of the swap, a fresh GM Goodwrench Replacement, with 462624 heads. the swap was successful, I did notice better power, as well as better mileage, but the idle was a small improvement, but still "shakey" or vibrating like it still had a bad carb. So, I was thinking that the reason, may have been the camshaft, being that it was originally a carbed engine. I checked for vacuum leaks....I plugged of all vacuum accessories(A/C, brake booster) at the manifold source. the only things I left were the PCV, EGR,MAP, and FPR...........Just the bare necessities. No leaks. Still a shakey idle. So, this last Feb., I swapped the cam out for a comp cams 12-388-4, at the suggestion of a Tech at Street and Performance. I also swapped the 624 heads, for a set of New 193 heads, as well as a full Ignition tune up, using all AC Delco Parts. Timing set at 6* Not looking to race anyone, but, to be honest, I dont think that there was much of a performance increase, as far as the seat of the pants dyno is concerned, but I was disapointed that the Idle was the same as before, even with new Bosch3 injectors. Again, I checked for vacuum leaks....nothing. So now, I am thinking that I need a tune. I knew I needed one from the get go, but the cost of the tune was prohibitive, as well as now, and the idle is really the only thing that has really been eating at me. the snap on scanner says 128 for the block learn( I`ll have to borrow the scanner again, but I remember that as far as data)and no trouble codes. I have sent private messages (on FSC, but they are here too) to the 2 people, whom I consider to be the TPI truck swap Guru`s, but I have not received any replies.....not as much as a "Buzz Off" or "NO" or "I don`t have time", or "dont want to help you". I would love to find somebody with the Truck TPI swap, with that smooth "Cadillac" type idle, whom has had the tune done, and find out if I can get info from them , to have a duplicate Prom burned....I know it wont be free, But I figure, that there have been enough of these swaps, to have these tunes available, without having to spend $500 at a dyno, just to have the dyno guy send the chip clear across the country for the burn....if I could take a TBI Prom, and put it in my TPI ecm, I would do it. TBI trucks Idle, and run Awsom, I know. I am a 3a tow truck operator, and Have seen plenty of them. Any help would be greatly appreciated! Thanks! Jim

Well really theres no reason why your current set up cant run as smooth as anything just needs a little work. For starters i think a good tune of the chip would be a good plase to start. I know its not really cheap or convieniant but with an incorrect tune it will never run right. This is especially true if you swapped on a later MAP style TPI system there alittle picky. The other thing you might want to include is what kind of parts are you useing? Meaning did you borrow this TPI set up off a 86 305 T/A or what year/car? The thing is there were differences between some 305 and 350 parts. Things like the prom, fuel injectors, knock sensor ect. Say for example you were running a 305 chip on a 350 then it wont run to good or say you have the 350 chip but the 305 injectors again = runs poorly. So i think the primay objectives here are to ensure that the fundamentles ofr your swap are sound by ensureing you have a good tune thats correct for your application and all the right equipment installed. Then we can really get right down into the troubleshooting at the component level.

Thanks for the reply , thunder.
All of the parts are from a 91 z28, 350, as well as all new sensors(ac delco), the injectors are new BoschIII 22 lb hr(yellow) i am looking for a cheap scanner to datalog, as i no longer have access to the snap on scanner that i was using previously. I may just have to bite the bullit, and the APU1 from moats.

Alright well while your working out the dataloging issue which i think would be a big help there are other things you may want to check out. Maby if you have an inductive timing light your can test all the plug wires to see if there all fireing or if you have ones that are dead or intermitten. Maby a vacuum and fuel pressure test would be a good idea. Although like I said earlier and im sure you already know MAP style TPI systems arnt very forgiving to changes and concidering virtually everything but the block has changed ide guess it would run a good deal better in terms of performance and smoothness with a good tune.

I have noticed that the timing moves around at idle...confirmed with timing light. Any thoughts?

probly did this but u disconnected the timing wire right? passenger side wheel well area

actually, my tpi is in a suburban, but yes i do disconnect the spout connector when setting the timing. the timing moves around when its connected, and at idle. Engine runs smooth in the higher rpms.

okay, so, I started the beast last night after letting her sit for a fe days, and she was running a bit rough , as usual. I decided to crawl underneath and look up to get a look at the spark plugs.....there was no outer arcing, but the porcelin looked like it was glowing blue, as if i was seeing what was going on in the spark plugs. I don think im supposed to see that, right? They are new delco plugs, but there is a possibility that i messed them up when i did the cam and head swap. any Thoughts?

Same problem here, low vacuum, shaky/stumbly idle. Been through ignition and fuel with no luck. Car drives down the road perfect but idles like crap, car is loaded up and getting in and out of gear is brutal. Let me know if you find something. I have been chasing this for years. I do my own chip/emulating for the computer, I can not tune the problem out. I feel your pain...

If your timing mark is moving more then Id say 2degs, then I was always told that was a sign of a weak/bad timing chain.

This will not solve all your problems. But a good tune needs to be based off a great/working motor with fresh tune.

You for sure do need a custom tune. Nothing is the same as its designed for.