austinc3

Greetings!

I recently installed a 700R4 transmission along with the entire TBI injection system into my 1976 Stingray. It is supposed to be a relatively easy swap, but I can't figure out why it is not running properly.

I am running ECM 1227747 with an ANLW prom from a 5.7L Chevy Truck.

It's sadly not making as much power as when the card was on there.

It also experiences random surging and backfires through the intake under heavy load. At idle it runs way too rich, I can smell it and it throws ECU code 45 (rich). And it is making a really funny sound at idle.. I have never heard anything like this come out of a GM TBI.. (see attached video)


I noticed that at idle the timing jumps around 5-10 degrees. If I remove the connector near the distributor to set the base timing it stays at 0 degrees steady so it's not a loose timing chain.

Idle vacuum jumps around too, but it stays around 15 in generally. Is that too little for a GM TBI? I am not sure if the previous owner installed an aftermarket camshaft, but the vacuum measured around 15 in/hg while I had the carb installed too so the low vacuum is probably not due to the swap.


I have replaced the cap, rotor, and wires. I swapped out the MAP and IAC sensors which did not help. The temperature sensor looks good in WinALDL so I have not replaced it. The TPS seems ok in WinALDL too, it measures at little over 4V at WOT. I have a brand new bosch fuel pump in the stock tank and measured the fuel pessure at 12.5 PSI.

Any ideas?

-Eddie

oldalaskaman

vacuum leak, o2 senser

diehrd

It sounds like Willie Wonka's car ..

Mark Riles

Have you posted this same question on a forum for GM TBI trucks? We can trouble shoot it but I suspect a forum that specializes in GM TBI injection would be the best place to get some opinions.

terry82

did the ecm and the tb come together or did you put them together .the injectors may not be right for your motor. if the tb came from a big block you have big injectors. the cam may not work with injection.

hugie82

When you unplug the advance the timing SHOULD NOT read "0" it should be @8-10 . That could be the problem right their. If you still have a heavy rich condition I would check your fuel pressure. TBI runs lower pressures than the TPI systems.

lionelhutz

How does the BLM, rpm, TPS, MAP sensor and O2 sensor data look at idle?

If I'm not mistaken, the initial advance is set to 0* in the prom but there is a 9.8* bias factor in the tune. This bias factor is subtracted from all ECM timing calculations. For example, if the timing should be 28* it takes 9.8* off and sets the timing to 18.8*. So, you have to set the timing 10* advance to compensate. Easy to compare the WinALDL expected timing with the real timing using a set-back light while the ECM timing wire is connected.

As others have posted, do the injectors match the tune?

I'd also suggest you get rid of the riser ring and use a breather that doesn't have such a drop base on it. Then, you can grind off that ridge around the TBI barrels to smooth the flow even more and open it up a bit.

The injectors do tick and it's easily noticeable at idle. Maybe you mean the engine sound but that could just be tuning.

lionelhutz

Might as well add a few other things.

Where is the O2 sensor? I hope you've got a heated O2 if you're running it in the collector of headers.

Are you getting set-up to do tuning? I doubt you'll ever get it running right without doing that, especially with more cam than stock. At one time, I was running a very similar setup with a Crane 268 cam and it worked well but it needed tuning.

austinc3

Hello,

Thanks for all the responses! Upon reflection Mark Riles is probably correct, I should have posted this in a TBI forum.

The O2 sensor is working, I can see it crossing back and forth in WinALDL. It is a three wire one, but I have not hooked up the heater, it seems to work fine though.

I messed around with the timing and that did not change anything it still has the funny sound and backfires when I jam on the gas from idle. :-(

The injectors are the orange/black type from a 5.7L chevy pickup, I swapped them out for a different (also orange/black) set and that did not help. I assume those are the correct injectors, or should at least be close.

I am wondering if that strange popping sound at idle is because the valve lash is too tight. When I got the car it has major valve-train noise because two of the rocker arms were extremely loose. Now I am wondering if when I did the valve job I accidentally made them too tight. I am going to try adjusting the valves again tonight and see what happens.

Mark Riles

Have you checked for a vacuum leak up to this point? Popping can sometimes mean it's experiencing a lean condition. Exhaust temperatures might also be considerably hotter too if that is the case. Vacuum leaks can be in hard to detect places like intake gaskets that do not seal properly around the runners or the front and rear intake seals. Spraying something like carb or brake cleaner around the base and front and rear of the intake would help you detect a leak.