I've having a no start issue that is sporadic, sometimes the engine will start and run just fine and other times it won't start at all, just turns over. It did this same thing with the stock L-98 but when I pulled the engine to be rebuilt I replaced almost everything in the ignition system hoping to eliminate this issue. But of course it didn't.

It seems to only do it when the engine is warm, is this a timing problem?
When its cold it fires right up, every time. But occasionally when the engine is warm it decides to sputter then do nothing. I've replaced the coil with a MSD unit, new distributor, new wires, new plugs. Also installed a new Walbro fuel pump and sending unit. I'm at my wits end with this thing, just spent Ten grand on parts getting the car built and now I'm having this stupid issue. Other than this one problem the motor runs great, pulls hard and everything. T-5 shifts great, suspension is tight, etc..

Now the car surges a little at idle, not sure if its because of the cam and stock tune but I thought about messing with the TPS sensor to see if I could get it to idle a little better. It's an LT4 Hot cam btw...


Any ideas on what to look for or check? I'm stumped on this car...

 

Are there any codes coming up?

 

Only for the O2 sensor, it's not plugged up right now since these headers don't have a O2 sensor bung in them. Taking the car to the exhaust shop to have one welded on along with the Magnaflow cat back installed.

I'm thinking the timing may be the culprit. Need to buy a timing light and check it, basically I stabbed the distributor to fire it up and have never moved it so the timing may be way off. Once the car cools off for twenty minutes or so it fires right up and runs great. Could the IAT sensor tell the computer the intake air temp is too high and cause it not to fire? These TPI motors are new to me as all I've dealt with is LS1's. So I'm learning. Thanks for the help

 

No
Checked for injector pulse ( electrics prob )
How old are the injectors? may be breaking down when hot
Checked hot and cold resistance of injectors? Are the plugs wet or not with fuel when no start ( fuel prob )

You invested all that $$ in a new engine but want to risk it by not setting the timing correctly?

 

I checked the timing today with a light and it was almost spot on. Haven't driven the car on the road, just been running it a little trying to get the bugs out. Good point though.

I did notice I had the number five and seven fuel injector connectors crossed which caused my misfire. I swapped them back and now it runs great, starts up first try every time even when hot. So I think I've fixed the hot start issue.

I took some time today to double check every connection, bolt and wire to make sure I didn't miss anything. Took it to the exhaust shop and got my magnaflow catback installed then went for a long drive. The car runs great, pulls great and idles perfectly. I'm very happy with it... just need a tune and everything will be good to go.

 

Shouldn't have done anything, TPI is batch fire so all the injectors fire at the same time.

 

Yeah, that really makes no sense at all. But, good luck. You will likely end up wanting new injectors. Personally, I would never risk a new motor on old injectors. I at least have injectors cleaned, tested and flow matched any time I replace an engine. Learned that lesson the hard way.

 

Batch firing injectors make no sense at all, but if that is true then whatever it was fixed itself. The car runs great now. And I see no point in swapping for new injectors whenever the old one's are in great condition. Mine were cleaned, tested and inspected btw. Everything on this motor is new.

 

Maybe the the plugs were not making a good connection on the injectors
and now you have it after swapping the connectors over ?

 

Great, nothing like a fine running motor.

 

Honestly I think that's all it was. The car runs great now, better than it ever has. Can't wait to get it tuned and just enjoy driving it this summer. Feels like a beast power wise so it should be fun once its broken in.

 

I remember many years ago in GM school when I first learned about batch fire injector control. I had always though that port injection must have each injector fire separately. But no, they fire all at once, every turn of the crank. Remember that the crank makes two turns for each firing of the cylinders(4 stroke). So the injectors all fire twice for each firing of the cylinders, or two injector pulses for each intake stroke of each cylinder. Sounds goofy but it actually works very well and by 3,000 rpm, the air and fuel movement is almost constant anyway. So for making power, it's really not much different than sequential, where each injector does fire individually. Sequential can be a bit more efficient.

 

That's interesting, never knew that. Thanks for the information on batch fire injectors. Learn something new every day!