I am sure that I just overlooked this in the forum and that someone has already talked about it. I just converted my 91 trans am from a 305 TPI to a 350 TPI. The engine block was a 68 block with flat top pistons and a mild RV cam, the heads are l98 heads. I bought the engine from a shop that said the engine was rebuilt. I had the prom re wrote from tpi motorsports to eliminate the airpump, and EGR along with the 350 tune. I installed LT1 injectors and a 52MM throttlebody. New plugs, Wires, Cap, and rotor. The Knock sensor, O2 sensor, and map sensor is new. I have a new summit harmonic balancer, and new headers with the air delete with an eld 3" exhaust. The flywheel is from a 1982 camaro that had a 350 in it.

The engine starts great however there is a vibration all the way through the rpm range and on acceleration the engine stumbles and cuts out. It is really lacking in power too. It feels like a 6 cyl on acceleration. I reset the timing and it is at 8 degrees right now. I have a idle at 6-800 rpms. I have checked for vacuum leaks and haven't found any yet. All the vacuum lines are new.

Help I am getting frustrated.

 

'82 Camaros didn't come with 350's. So, if the flexplate came off of a 350, it didn't originate in an '82 Camaro.

Make sure you have all of the spark plug wires going to the proper cylinder. It's easy to mix some of them (like 5 & 7).

Then, make sure you're getting good spark to each cylinder. That may involve doing a resistance check of your spark plug wires, unplugging one wire at a time, pulling plugs to check for one that isn't firing, etc. I know you said that stuff is all new, but that doesn't mean one isn't bad.

Did you keep your 305 PROM? Doesn't sound like it, but just making sure.

 

The engine number that was on the 82 said 5.7 on it so I know that the flexplate was from a 350, The prom was rewritten for the 350 tune, egr delete, and smog pump delete, None of the wires are crossed. I will have to recheck the injectors and plugs.

 

Im confused. As Five 7 said there was no 5.7 offered in 82. I have seen special edition 350 TAs but I believe that wasnt till 84. What engine number are you talking about? Is it from the emissions label? Are you saying that you looked up the engine code? Im thinking youve got the wrong flexplate. That would explain the vibration, not the cut out. Check fuel pressure, should be 35 at idle, jump to 40 on accel. Check spark at each plug. Check for spark drop out. Ign mod/pick up coil failures are common. Perform a power drop test. Pull one plug wire at a time and note RPM drop. They should all be even. Look for one or more cyl that shows no response.

 

the engine that was in the 82 had been replaced long before I got it because the block number read that it was from a 85 truck. Yes I looked up the code. I know it was a 5.7. You can't put a 305 flexplate on a 5.7. The crank flange diameter is different, or at least the stock 91 305 flexplate wouldn't fit the hub on the 350.

I will check the plugs again and will check the fuel pressure. That is some good info on the pressure. Thanks

 

It's not 305 vs. 350, it's 2-piece rear main seal vs. one piece rear main seal that changes the crank flange for the flywheel mounting.

 

try swapping ecms prom ? test the advance?

 

ok so I checked spark and all are good and firing. So I did a temp check on the headers. number 1 cyl is running at 600* 2 is380* 3 is 380* 4 is 380 5 is 360* 6 is 550* 7-8 is 365* So what do you all think

 

looks like cylinders # 1 & 6 are running lean with those temp differences.

 

Sounds like a couple dead injectors

 

I would agree with the lean condition but I was thinking a couple of lazy lifters or weak valve springs. I hear a tapping on those 2 cylinders.

 

High temps definitely point to bad injectors. About the noise, have you done a compression test? Cranking compression and then running compression. Cranking will show any glaring issues and running can point out valve train troubles. Also easy to pull a valve cover and look for problems. Use a dial indicator to check valve lift. Verify that cam lobes arent flat. Check lifters.

 

Well I finally got a chance to work on the car again tonight. This is a first in about a week. I started looking around and found bare wire on cyl 1&3 injector wires and they were laying on the intake. That could be some of the prob. I checked all the injectors and Ohm'd them all out while hot.

1. 15.1 2. 14.9
3. 15 4. 14.8
5. 15 6. 15.1
7. 14.9 8. 15

I haven't gotten a chance to do a compression check yet but already the car is running alot smoother with the wires fixed. The next question is the reading on the injectors is this normal.

 

Injector impedances are all pretty close and range around 15 ohms. Thats okay. Puzzling though. Your exhaust temp test showed trouble on 1 & 6, not 1 & 3. You say its smooth now. Or just not as rough.

 

It is just not as rough. I did notice that I am getting alot of crankcase breather vapors, This could indicate bad rings, or a hole in a piston or it could just be that the block is a high nickel content block and is taking some time to break in. However I took it out for a short spin, about 10 miles and when I got back I noticed that my exhaust started smoking. I am thinking that I need to pull the engine back out and tear it down to invigate.

 

That may well be where you end up. Before you pull the motor though, perform a compression test on all eight. Then, follow with a leak down test. That will tell you if your ring seal is good. Also, when doing the compression test, lay out your spark plugs and compare them for color.

The varying cylinder temps point to an imbalance in combustion temps. Now that the motor's been run a bit, the imbalance should show up on the plugs. Look for some that are especially dark or light. Maybe some that look a little too clean and new. Reading and decifering spark plugs can reveal alot.

I assume that you have good oil pressure. You havent mentioned it so I guess you havent noticed a problem there. A motor thats been sitting needs good pressure to pump up the lifters.

 

I have an injector,#7 that has no Ohm reading, will this injector still work at higher rpm's, but, at idle cause the engine to stumble and make the idle inconsistent?

 

yeah the oil pressure is good. I did figure why the engine is stumbling. I set the timing at 6 as per the haynes manual, but I have a '68 350 in this car with 10:1 compression and a mild cam. I stepped the timing up to 13 and the stumbling stopped. I am 98% sure that the vibration is coming from the flexplate.

A dead injector usually remains dead.

 

I did a fuel pressure check and the needle fell pretty fast. I believe the dead injector was leaking too. I think that maybe its the reason why it still ran on all eight cylinders. Have you heard of this happining before?

 

Have you done a temp test on the cylinders? That will tell you if the #7 is getting fuel at all. Also do to the age of your car look for cracked caseing on the injector wiring harness. It could be shorting out giving you a dead injector. However if the injector is not firing at all it will give a vibration, or a skip. I have never had a injector read 0 but if it does just get a new set of injectors. If your pressure is dropping very fast you could have a falty pump or a bad regulator. I have had both do that to me. Start with one problem at a time and look at the simplest fixes first.