lt1 starts and dies right away, runs ok after it starts

[Craig 94 TA GT]

Steve (Z ya later) and I have interchanged a '93 ICM with a '94, but that was a '94 ICM on a '93 Z28. It worked fine. I know that they are different and I think '93s read the tach from the ICM rather than the PCM (not positive on this), so I'm not sure if you can go the other way around. You might want to check around to see if you can swap it temporarily with one of your '93 ICMs. However, it would be unusual if it was the ICM though because my experience with an ICM going out was either constant misfire or a no-start condition.

[Injuneer]

If it starts better with the throttle on the floor, it may be flooding iwth excess fuel. Holding the pedal on the floor puts the PCM into "clear flood" mode, where it cuts back on the normally rich cold-start A/F ratio. That could be the sign of leaking injectors (would show up be seeing how fast the fuel pressure bleeds down on shutoff), or a coolant temp sensor showing a very low temperature.

[Trans Am]

today i replaced the intake air temperature sensor and its still the same . seems to hold fuel pressure ok , even after a long time its still high , not tested with a gage though.
Could the coolant temperature sender for the ecu be bad and cause this?

It runs really bad , shaking , then all of a sudden runs smooth after a little while . if i hold the accelerator and let it rev a little at startup it usually is fine .
I noticed the tachometer needle move , like jump a little when i turn the key to run without starting the engine

Have not tried swapping the ICM s because i tried that , a 94 95 icm and 93 t/a, it didnt start

[Injuneer]

If it starts better with the throttle on the floor, it may be flooding iwth excess fuel. Holding the pedal on the floor puts the PCM into "clear flood" mode, where it cuts back on the normally rich cold-start A/F ratio. That could be the sign of leaking injectors (would show up be seeing how fast the fuel pressure bleeds down on shutoff), or a coolant temp sensor showing a very low temperature.

today i replaced the intake air temperature sensor and its still the same . seems to hold fuel pressure ok , even after a long time its still high , not tested with a gage though.

Could the coolant temperature sender for the ecu be bad and cause this?

Why would you replace the IAT sensor? Doesn't make any sense at all.

How do you determine the fuel pressure is holding "ok" without using a pressure gauge?

With regard to the coolant temp sensor, did you even read the info I spent time posting to try and help you...... I don't think so. Appears I am just wasting my time, so I'll back off and let others help you.

[Trans Am]

Why would you replace the IAT sensor? Doesn't make any sense at all.

How do you determine the fuel pressure is holding "ok" without using a pressure gauge?

With regard to the coolant temp sensor, did you even read the info I spent time posting to try and help you...... I don't think so. Appears I am just wasting my time, so I'll back off and let others help you.

i had temepreature sensor stuck in my mind lol , and had a spare IAT sensor and replaced that to see what happens. i know there are a couple of coolant temperature sensors on these cars, not sure which one sends signal to the pcm, i know IAT sends a temperature reding to the pcm so i replaced that to rule it out.

This is not a mainstream car here that i can take to any garage , and many gauges like fuel pressure gauge dont fit , no way to scan this and its a 95 so its ann obd 1 with obd 2 connector which makes thinks more difficult, so i have to work with what i have. sometimes its easier and cheaper to replace some parts than take it to a specialized garage. there is one in town here but has no scanner , wants me to leave the car there and he takes it to some other place 30 miles away to get it scanned , and it took him 3 days to replace an opti which i can do in an hour ( done it a few times on the 93 t/a )

I had fuel pressure problems with the t/a and the formula holds pressure in the fuel rail , when i press fuel sprays out , not squirts like the t/a when the fuel pump is bad. and i know the lt1 do not need very high fuel pressure to work , so i decided its ok and moved on looking for something else.

Fred, the info you posted on the forum has helped me many times , and i am grateful someone who knows what they are talking about takes time to help solve problems, thank you , but you dont have to treat others like they are idiots, yes you know more about these cars . i have an ideea too and want to learn more to understand them better not someone to tell me what to replace and how. I m sorry you think i just ask and disregard what you reply when you try to help me, i was looking for a coolant temperature sensor now, or the resistance it has when at say 20 degrees celsius, am going to put a resistor in its place if i cand find one ( takes about a week to get parts here usually if they are not in stock)
If still the same problem , i ll probably take the opti apart and clean it or replace it with the spare one i bought a while ago.
I m not asking for step by step guides to fix my car, i just want to understand better how the lt1 works.

what would a bad IAT cause? I ve learned bad coolant temperature will put the engine in a rich start mode like when its really cold outside .
What would a bad TPS cause? or a bad IAC? bad MAP ?

Bad opti ? could that cause that ? the 8 slots in the opti that are used to determine the position of the cylinders , could that be bad? if so what would make it run ok all of a sudden after a little while?
i think the other part of the opti pick up part is ok since the car doesnt miss at all and runs strong , idles normal after a little while after startup.

a little frustrating to have to work on it without proper tools, i m trying to eliminate possible causes .

[formula_gramps]

No offense T/A but your diagnostic approach to this point is sounding equivalent to listing out all the possible problems of an LT1 and putting them on a dart board. Yeah.....eventually you might hit upon the problem but there's a better chance that you won't.

In fact, randomly swaping out parts is a good way to accidentally introduce a second problem into the mix. The object here is to try and narrow down the number of possible problems by eliminating bunches of them at a time. I'm sure you know that one strategically executed test can often knock a half dozen "possibilities" off of your list.

Right now, it doesn't sound like you've narrowed it down to either fuel or ignition related. That's been the starting point for automotive diagnostics for about 100 years now.

I'm not sure your test for fuel pressure means much of anything, since you have described the problem as being intermittent. If I had the same problem with my 94 Formula I'd be thinking about inconsistent fuel pressure/volume which could be as simple as a fuel filter loaded with crud or a pump on its way out.

Mainstream or not, there has to be some way to get a F/P gauge on that car if for nothing else, so you can rule out a couple of obvious possibilities.

You are right about something though: Fred does know a hell of a lot about these cars, and it seems like he was just trying to help. I see no evidence in his post that he was trying to treat anyone like "an idiot".

[Trans Am]

the car runs perfect, strong, not missing at all , that makes me think theres no fuel issues. just starts and dies, or starts and runs rough for a little while , then its like it realizes what is wrong and uses something else to run, like switching from maf to speed density.

I m trying to figure out what makes it run ok all of a sudden after a little while after startup.

i think bad fuel pump or fuel pump going bad would make it run lean under wot, or miss. even if i turn the key to on a few times before i start the engine it still starts and dies.

i m not asking for instructions what to do, i ll figure that out according to what i have to work with here, and theres no need for anyone to tell me off and ask why would i do that .
might be cheaper to just replace everything than take it to a garage and get them sort it out.
Just want to learn how it works, what would make it run ok after like 10 seconds after startup.

[Craig 94 TA GT]

You have not ruled out fuel in my opinion because the leaking injectors possibility was not addressed. In theory, if the injectors are leaking and you have a flooded condition, causing it to run terrible for a bit. A fuel pressure checker kit is cheap and can be purchased at a lot of places http://store.summitracing.com/partde...?part=HYP-4004

A bad IAT will not cause your problems. I have run without an IAT a few times, and the SES light doesn't even come on sometimes, when it's not installed. It ran without issue.

Also, the first "scan tool" I bought was one shipped from Europe. It hooked up my laptop to the OBD1 port. I think it was less than $40. Diagnostic tools will save most of the guessing game.

[FroSSty]

This is sounding more and more like leaky injector(s). I had a similar problem in my Jimmy. It would start hard and the idle was terrible until I got on the road. then it ran pretty good. It turned out to be a leaky fuel pressure regulator which is inside the intake.

[Trans Am]

ok, i had some time to work on the formula, checked for fuel pressure in the fuel rail, but there was nothing, i m not sure it should hold pressure after a week?

turned key to run a few times and waited a couple of minutes, since the resistance values of the iat and ect are the same i connected the spare iat to the ect connector and it started up ok , let it run for like 10 minutes, turned it off, started it up again after 5 minutes, all ok, even if i didnt hold the key to start for as long as i should have it still fired up, so i guess its the ect like Fred said first .

Thanks for the replies

[Trans Am]

ok, its not the engine coolant temperature sensor, i replaced it , looks like it was ok , still not the same readings as the new one but not far
i m not sure now where to go next ...still no scanner to check for fault codes , or for sensor readings
Car still runs strong , no missing , but running very rough and shaking bad until it suddenly runs smooth again

[Injuneer]

If you don't have a scanner, how did you determine that the ECT sensor was "still not the same readings as the new one but not far"?

[Trans Am]

If you don't have a scanner, how did you determine that the ECT sensor was "still not the same readings as the new one but not far"?

i used a multimeter and the info here (thanks rob)
http://shbox.com/1/4th_gen_tech2.html#ect

They should have been closer i think , but the difference was about 1000 ohms, both at ambient temperature.

i ll try to find a fuel pressure gage next and start over testing properly, might take a while to find one though.

I have a ractronix fuel pump fot the lt1 with the upgraded wiring harness, i might fit that as its probably better to have a walbro there if i am going to use nitrous .
this is annoying as i was going to fit the zex dry kit i have, and ngk tr 55 spark plugs, i even got a spare set of fuel lines so i dont have to cut the ones on the car ( for the in line booster pump )
i wont use that until the car is runnin ok

[Injuneer]

Its possible to install an inline booster kit without cutting or altering the stock fuel lines in any way. I did it with my NOS dry kit. The instructions are in the NOS online install instructions for the 5176 kit.

[Trans Am]

ok , i just installed a racetronix-walbro fuel pump, not the gss 340 but the earlier lt1 specific pump. starting problem still there.
i will lift the fuel rails and check if the injectors are leaking next... any ideeas?