Question : Engine now won't start after sitting for two hours

[tom.whitez34]

Hi, I thank you in advance for any suggestions and help on my problem. Had re-conditioned (from local Napa Parts store) fuel injectors installed about a year and half ago. Not sure if they are the problem. The engine has always fired up right away and still does when totally cold (sitting overnight). But when the engine was still warm (parked for less than an hour) it would definitely take longer to fire up (about four seconds of cranking). But now, it still starts instantly first thing in the morning and re-starts right away when I just go into a store for about half an hour. But here's the problem that just started two days ago. If I leave it and try starting it after two hours or so, it just cranks and won't fire up. Doesn't even grab a little, just cranks. It used to be just hard-to-start after sitting for 2 hours but it would start, now it just keeps cranking. These are the only clues I have offer... a smell of gas in enclosed garage after cranking and not starting (not a super strong gas smell but definitely a gas smell because the doors are closed). I can also smell gas out of both tail pipes (actually smells like raw gas). No gas puddle underneath car or near the plenum that I can visually see. Took off plastic cover at the front of the plenum and the front three injectors and the surrounding area looks dry. Put my nose really close around the plenum area and can NOT smell gas here though. Battery is fine (strong cranking power). Full tank of gas. Thought it might be a fuse or the fuel pump relay or fuel pump but the warm no-start happened two days ago. Scenario was... it wouldn't start after sitting for over two hours; so I let it sit overnight; it fired up right away the next morning; went out to the grocery store; started up again no problem after 1/2 an hour; came home and parked it; came out to try to start it about 2 1/2 hours later and warm no-start happened again (just cranks). Has anyone come across this problem before. I thank you again for all your suggestions and help on this, thanks, Tom.

[brian89gp]

If you smell gas then it might be worth checking spark. Check the ICM and crank sensor, heat soak has been known to cause those to malfunction.

It is possible that the injectors leak down at which point the the engine floods and requires sitting overnight to evaporate/drain off, but its odd it would do it after two hours but not half an hour. What year car? The 91-93 ECM has a flood clearing function that if you WOT while cranking it disables the fuel injectors in order to clear the flood. If it is indeed flooding this test would confirm it....used it many times when finding the right settings for 36# injectors.....

Also check fuel pressure at the rail in the morning, after 0.5 hours being shut off, and after 2.0 hours being shut off.

[tom.whitez34]

Thanks for the input Brian. Here's an update as to what happened this morning. Car sat all night. It started immediately on first try this morning. I didn't let it warm up for that long (4-5 mins) (thermostat did not even kick in yet) and shut it off. It started again right away. Let it run for a few more minutes, then turned it off. When I tried to start it again, it wouldn't start, just kept turning over, just like the warm no-start situation yesterday but now it has the no-start without sitting for over 2 hours. Tried the WOT on gas pedal while cranking but no change. I don't smell any gas this time. Stumped... I'll check a few things more and post again, thanks.

[tom.whitez34]

Update: Fixed! A week or so after the intermittent starting and not starting issues stated above, the engine wouldn't start at all, just strong cranking. Did smell fuel again. After reading really helpful posts from this site (thanks!), narrowed it down. Because I could smell fuel, CPS was ruled out. Chances of all three coils failing at the same time are slim. Checked for spark again on the front bank and found none this time (I had spark when the problem was intermittent a week ago). It turns out it was a dying (but not dead) Ignition Control Module and now confirmed it's a dead ICM. Installed a new ICM and fired up right away. Thanks for all the great documented info on this site! It definitely helped to narrow down and finally find the problem. Obviously, being the "great-reliable" Z34 engine, I will be back again when the next problem arises. Merry Christmas!