I'm sure there is a forum post on this somewhere.... but I can't find it so here we go. If this has already been discussed elsewhere, please direct me there. Thank you.


My 1989 Firebird with a 5.0 TPI has a hard starting condition during the summertime after sitting overnight and once the engine is completely cooled down. In the morning, the car will crank and crank, cough, and after letting the fuel pump reprime, it will come to life.


However, during the winter with ambient temperatures in the 40-to-50-degree range, the car will crank momentarily and come to life mostly like any other older vehicle would on the first try. In other words, the car starts "normally" during the winter.


I've tested fuel pressure and although it shows good pressure after priming one time, it does bleed off over the course of a couple hours. Is that an indication of a bad check valve/fuel pressure regulator? OR is that normal for it to bleed off that quickly? I'm sure the answer is simple and is completely flying over my head, but any help explaining why the car is experiencing these weird starting issues would be fantastic! Could it be because of air density changes in lower ambient temperatures? That is my hypothesis. But I have absolutely no clue.

 

Others might have more direct troubleshooting with a case like this but

When it's warm again and only crank, check fuel pressure, spark and injector pulse. If one if those is missing then you have a path to start at.
check the resistance of the coolant temperature sensor and compare it to a CTS chart. Coud be faulty and the ecm thinks it's a different temp, causing fueling to be incorrect.

 

Bleeding off after a couple hours is ok. I get suspicious when it bleeds down in a couple minutes. aliceempire's diagnostic ideas seem like a good place to start. Another easy check is to ohm the injectors cold, and hot just to see if you've got any obvious failures there (although I would expect you to have the opposite symptoms, it's a half hour job that is readily accessible).

Have you closely examined the major electrical ground points? Weak grounds can cause bad issues when the weather warms up.

 

Thank you aliceempire and Komet. Super great ideas a couple of which I hadn't particularly thought of. Checking the Coolant Temp Sensor is something I've thought of but never decided to do in part because it was replaced not more than two years ago. But I've already ran into issues with new parts going dead quickly so that is something I will look into. The car itself runs beautifully otherwise so I don't think it would be an injector issue but you never know. I'll definitely dive into a couple of these troubleshooting steps and report back what I find. Thank you!!

 

My L98 has done the same thing for years. The Corvette guys call this "extended crank" and I've not seen a fix for it. On my car I replaced the injectors, FPR, a couple fuel pumps, no help. After it sets for a couple weeks, or on a real cold morning it starts right up. Starts and runs fine when warm, 23 mpg on mostly highway driving. I just gave up.

 

1989 so no Cold start injector, right?


Try change the coolant temp sensor, especially if its original...........it could just be telling the ecm all kinds of weird temps giving the car too much fuel when it needs less, or too little when it needs more. it could be out of range but the ecm sees it as working properly... happened to an old camry I had and my S-10.



Its pretty cheap and easy to get to.