I just completed my 2.8 to 3.4 pushrod engine swap and have started to break-in the engine. I must say I do notice the extra power it has.
Now I need a little help with this issue. When I quickly accelerate in 3rd, 4th and 5th gear, I get a momentary rattling sound from the engine. If I accelerate slowly, I get no noise at all. Does anyone have an Idea what this is? In this engine swap, I reused all parts from the 2.8. Help!

Hmmm, could you be a bit more specific about the "rattle".

You mentioned that it only happens momentarily when getting heavily into the accelerator but not during a milder acceleration. This sure sounds like burst knock to me (rapid increases in cylinder airmass, ECM hasn't pulled out enough timing - result is knock until revs increase or ECM compensates).

What tuning has been done?

Cheers

Sounds like knock (preignition) to me too. You may be running lean

which injectors did you use?

egr stck open?

quote Originally posted by TiredGXP: Hmmm, could you be a bit more specific about the "rattle". You mentioned that it only happens momentarily when getting heavily into the accelerator but not during a milder acceleration. This sure sounds like burst knock to me (rapid increases in cylinder airmass, ECM hasn't pulled out enough timing - result is knock until revs increase or ECM compensates). What tuning has been done? Cheers

It is more like pinging or knocking, like you guesssed. If it is my ECM, what can I do? I just had it timed by a mechanic, however he is not a Fiero specialist.

quote Originally posted by svocal: I used the original 2.8 injectors.

Some people have used the 2.8L injectors (15 pounds), but the standard size for a 3.4L engine is 17 pounds, which is what I run with my own 3.4L engine swap.

quote It is more like pinging or knocking, like you guesssed. If it is my ECM, what can I do? I just had it timed by a mechanic, however he is not a Fiero specialist.

This might be your problem. There is a special procedure to set the timing in our cars. It requires that the "A" and "B" terminals of the ALDL be shorted together. You then take timing readings from the number 1 and number 4 cylinders. The average of these readings is your actual timing.

quote Originally posted by project34: Some people have used the 2.8L injectors (15 pounds), but the standard size for a 3.4L engine is 17 pounds, which is what I run with my own 3.4L engine swap.

Thanks project34....you've been a great help so far in my 3.4 swap.
Since I ordered the 3.4longblock from the engine builder, and it did not come with 3.4 injectors...where do i get the injectors from? Do I go to a local auto parts store and say I need the injectors from the 93-95 camaro 3.4? Is there a specific injector?

You will also need to have the ECM reprogrammed for the 17Lb injectors, or it will run rich (maybe not at WOT, but all other times), thats assuming you used the Fiero ECM right?

You say you just had it timed, try pulling a degree or two of timing and then see what happens. Id almost bet that fixes it. That or fill the tank with premium, which will help delay the explosion of the cyl charge. (actually it just makes it harder to ignite)

Most people dont need to use the 17lb injectors, so Id bet its just the timing is set a little too aggressively, the guage on the harmonic balancer isnt neccessarially the most accurate thing, or the mechanic could have been thinking he would do you a favor and give you a couple more degrees timing. Thats assuming all else is well with the engine (IE no vac leaks or SES light)

quote Originally posted by svocal: Since I ordered the 3.4longblock from the engine builder, and it did not come with 3.4 injectors...where do i get the injectors from? Do I go to a local auto parts store and say I need the injectors from the 93-95 camaro 3.4?

That is one option. Another is to do as I did and get aftermarket, Accel brand, 17-pound injectors from Summit Racing Equipment ( http://www.summitracing.com ), ordering part number ACC-105617. The "17" at the end of the part number refers to 17 pounds. The "6" in the part number designates one set of 6 injectors.

Even with the 17's it will run lean at the higher RPM's and load.

My 85 stock prom was lean at the upper end and had to tune it a little or I had a fair amount of Knock.

You might notice it's does not knock or does it very little when you first start and the engine is cool. That is because the ecm keeps it richer until it warms up. Once your up to temp it will knock plenty if you apply much load.

quote Originally posted by svocal: If i'm running lean, what is the corrective action?

If the car is running perfectly and you still have fueel pinging.
bigger injectors. Better fuel pump. adjustable fuel pressure regulator.

A 20 year old fiero fuel pump can have problems to flow enough for a 3.4.

[This message has been edited by timgray (edited 05-04-2008).]

You DO NOT need bigger injectors to stop the pinging. My 3.4 swap ran FINE for thousands of miles with the 2.8 injectors. The first thing that i'd try is make sure the timing is set correctly, and get a tank of higher octane gas. cheeeeezz ...............

Thanks for all the feedback.
At least now I know where to start. I had a new fuel pump installed during the swap.
I started using 91 octane and did notice a drop in the pinging/knocking nosie.
I''l have the timing rechecked and adjusted as suggested. I hope that will take care of the problem.
If that doesnt fix the problem, I'll then look into changing the injectors.
I dont know too much about the ECM, so if i have to modify/change the ECM...how/where do i go?

If re-setting the timing does not cure the problem, there is something else wrong with the existing engine set-up. I'd also be tempted to check all the exhaust pieces to make sure they are secure. Adding extra parts is just a bunch of hooey that will waste your money - been there, done that - but the injectors are about $200 from Summit, so be my guest. If you wanna mess with the ECU, I'd suggest doing the ECU upgrade that Darth Fiero posted; he can care of re-programming your chip.

https://www.fiero.nl/forum/Forum2/HTML/079574.html

[This message has been edited by PaulJK (edited 05-05-2008).]

Okay....
I had the timimg pulled back a bit...and sure enough it got rid of the noise.
However..I now can now notice a slight decrease power when I accelerate. Is that a trade-off for the knocking noise?
Can this still be fixed?

It can be fixed, just have to find someone who knows what to modify in your timing table and burn a new chip for you. (Requires logging data, preferably on a dyno, modifying timing, burning a chip, or using a pc to emulate the chip, running another dyno... until you get to the point where timing is set for max power without knock.)

A better solution may be to move to the 7730 ECM with a kock sensor - have you checked out the thread on that? I think that Darth Fiero has a couple of tunes for that ECM that he can burn into a chip for you.

Tuning is so much easier with OBDII systems where you can just reflash the ECM through the diagnostic port.

Cheers

Thxs for the suggestion. I'll give Darth Fiero a try.

svocal, we haven't seen from you a follow-up post to this thread in over a month. That would seem to beg the question, "How is your 3.4L engine swap project going?"

I've got the same problem you describe, except I just replaced my '88 2.8 with an '87 2.8.

I noticed that under steady (not hard) acceleration, I get a knock between 2500-300rpm, but only in gear. If I punch it, I can't hear the knock until the rpm's are slowing - at around 2500-3000 (I have an auto trans, so the rpm's don't just suddenly drop off like a stick).

I'm going to try some high-test fuel tomorrow to see what happens. I know that when I was checking/resetting the timing, I over-did it a little and could hear the knock in neutral, but backed it from 11-12 to 9-10 and it would only do it in gear.

I also notice that when cold, the rpm's stay at 2,000, but when warm, it goes up and down between 1000-1200 every few seconds. Maybe I need to check into a clogged EGR.

Jeez, I hope that is the problem. I just got this engine in there and the guy I got it from said it was just rebuilt! I do have a brand new 3.4 waiting, just in case, but I'd rather save that for another car.

Thanks for posting this thread!

[This message has been edited by Saxman (edited 07-19-2008).]

Sorry it took so long to get back to forum.
Thanks to everyone in the forum for giving me suggestions, tips and extensive knowledge on my 3.4l conversion.
I couldn't have done it without you guys.

My diablo replica now has that punch i was looking for. Its a far cry from a V8, but im happy and pleased with it.
I can punch it and burn the tires at the stoplights when necessary. I not a speed freak, but I do enjoy the considerable punch.
The total cost came out to be about $4000. Not to bad. Once again...thxs to everyone for all your help.