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Engine SwapEverything about swapping an engine into your Third Gen.....be it V6, V8, LTX/LSX, crate engine, etc. Pictures, questions, answers, and work logs.
I have a 1990 firebird transam with a 305 with multiport fuel injection. I put the multiport fuel injection on a 383 stroker { a older block 4 bolt main, I had the manifold center bolt holes milled so it would be excepted}
The car ran ok initially with a cheap prom off the internet but timing was almost 30 advanced.
The engine ran lean for a while on the cheap 350 prom and now with everything else I added it wont idle and backfires on occasion. It is fouling plugs fast now while I'm trying different stuff. I cant get more than 7pds of vacuum and cant find any leaks.
I will list what else I did in the swap.
Professional build sheets below.
Added Parts:
B&K 58mm Throttle body
24 pound Excel injectors
Dougs shorty headers
Maf sensor
new IAC which helped tremendously with the Idle but did not last
new distributor
custom prom
changed computer to see if it was the culprit
This is my first post and I cant express how frustrating this has been, I cant begin to tell you what I've checked and rechecked three to four times.
I'm very very close to tossing a ton of money down the drain and going old school carburetor and manifold. (Ill leave that for another post because I have questions for that as well.
Ive read many posts and answers and I thank anyone who responds in advance.
The car ran ok initially with a cheap prom off the internet but timing was almost 30 advanced.
:shrug: If it ran OK, what's the problem?
You say "multiport"; I'm guessing this is TPI then?
Let's start with the simple stuff. What's the fuel pressure WHILE IT'S IN THE ACT OF SCREWING UP? That is, while you're diving down the street, and it does whatever it does. NOT while it's sitting in the driveway idling with the hood up; we need to know what it is WHILE IT'S IN THE ACT OF SCREWING UP. Tape your FP gauge to the windshield and have your assistant record observations at moments that it runs good / bad.
I can think of few worse series of cams you could have put in there. That's likely to be one of The Problems, if not The Major Problem. Might want to try something more specifically designed to the requirements of TPI (if indeed that's what you mean by "multiport"). I'd suggest one more about like this https://www.summitracing.com/parts/cca-08-501-8 or this https://www.summitracing.com/parts/cca-08-302-8. If it's an older block you might want to have them grind it on a "retrofit" roller core. You'll need link-bar lifters and a cam button to go with it.
A 90 model shouldn't have had a MAF sensor to begin with. It might be interesting to know how that came about.
Your tune is probably wrong for your combination, also that cam is very not what the TPI wants.
Exactly. Not sure what "cheap chip off the internet" means, but yeah the tune is likely all wrong and that cam is probably not suitable for a street car let alone for EFI.
That series of cams is designed for poseurs who want to wow all the 8-yr-olds at "square inches of krome" contests in grocery store parking lots on Friday evenings. Which is not to say that that's not a "valid" objective; after all, if that's how somebody wants to use their car, it's not hurting anybody else so why should I have a problem with it; only, it's NOT consistent with making the car produce the most power, be the most fun to drive, and all that. And worse FOR YOU, TPI requires cams to specifically support the "tuned" aspect of its runners; a cam that "lopes" equally specifically DEFEATS that feature. Get it OUT OF THERE, put a TPI cam in, and get a decent tune. There are people on this site that can help with that.
I'd be more worried right now about the backfiring and the fact that it's a Comp cam...........you better pull valve covers and crank it over to see how many lobes are flat.
Sorry for the delay got covid again. Ill tell you this first the original 305 80 thousand miles started having problems like back firing and under load it had no power. I took it to a shop they put a couple of injectors in it with no luck. being that it was a old tpi system it was full of vacuum leaks and since it was my plan all along to put a new engine in it I figured now was the time. I had some one put the engine in for me because I had no time to do it. They gave it to me and it wouldn't idle I took it home put a new IAC in it and it ran good for about a month, although every once in a while it would back fire out of the blue. I got a new computer, distributor, new professional chip, even another IAC. Im ready for a new manifold and carburetor. Which brings me to my next question if I cant figure this out. What all do I need to buy. Suggestions?
Still the same recommendation. Nothing that's been posted since then has altered it in the slightest.
There are other vendors that can supply cams in this general range. But one way or another, you need to get that POS "Thumpr" out of there, and put in a cam that is SPECIFICALLY SPECIFIED as being compatible with TPI, such as these are. Between those 2 the 302 grind is probably the better for your situation.
I'd also like to hear more about this MAF sensor that was put in. A photo would help.
I bought the engine complete from a long time builder it was available he had a good reputation, he was used to building 1/4 mile 1000plus hp. I was in a hurry mistake one the car is actually my son's 17 and I didn't want to wait all summer to finish it. To top it off I have Zero experience with TPI, my last car I sold 6 years ago was a 68 Road Runner 440 I actually enjoyed working on it.
You say "multiport"; I'm guessing this is TPI then?
Let's start with the simple stuff. What's the fuel pressure WHILE IT'S IN THE ACT OF SCREWING UP? That is, while you're diving down the street, and it does whatever it does. NOT while it's sitting in the driveway idling with the hood up; we need to know what it is WHILE IT'S IN THE ACT OF SCREWING UP. Tape your FP gauge to the windshield and have your assistant record observations at moments that it runs good / bad.
I can think of few worse series of cams you could have put in there. That's likely to be one of The Problems, if not The Major Problem. Might want to try something more specifically designed to the requirements of TPI (if indeed that's what you mean by "multiport"). I'd suggest one more about like this https://www.summitracing.com/parts/cca-08-501-8 or this https://www.summitracing.com/parts/cca-08-302-8. If it's an older block you might want to have them grind it on a "retrofit" roller core. You'll need link-bar lifters and a cam button to go with it.
A 90 model shouldn't have had a MAF sensor to begin with. It might be interesting to know how that came about.
After reading all the replies and the fact that even though I know what your saying is right if I change the cam it wont explain why the 305 in the end had the same problem. I have lot's of new parts forsale the TPI is not all that important to me it's all coming off and a carb and manifold is going in. Any Suggestions?
A tuned port even with a correct tune falls flat on its face at around 4800 rpm, if you want fuel injection and it to actually compliment the engine you should really look into buying a standalone efi system like a holley sniper rather than trying to piece together a severely outdated system for the same money. Ultimately it’s your car and it’s up to you what you want to do, fitech does sell the modernized ECU for it but it really just makes more sense to go holley efi at that point if you’re worried about power.
