Please Help me Understand [Archive] - GrandAmGT.com Forum

PDA

View Full Version : Please Help me Understand


packman
08-10-2011, 01:34 PM
Very first post on here.
I have an 02 Grand am gt (140,000 miles). On hot days (95 degrees or hotter) after getting the car to normal running temp. and turning it off. 5 min later it won't start. It will crank strongly tho. After some time it will cool down and start up. I'm getting no codes at all. When it does not start I am still getting fuel delivered but no spark at all. Has new plugs and wires Battery and alternater. I have read that the car will still start with the camshaft sensor disconected however mine will not. Could my crank sensor be going out making the car rely on the cam sensor? could someone please tell me how the crankshaft sensor and the camshaft sensor and the ignition control module all work together because I believe somewhere in these three parts lays my problem and they are a little expensive to be replacing to see if that was the problem. Just to add when the car is up to running temp on those hot days I am getting a flutter on the rpms when sitting at red lights but doesn't ever stall but once I start going there might be a little sluggishness but not really noticable when the rpms are up past 1500. I'm trying to fix this problem before my car will no longer start at all. Any help to gain knowledge and fix the problem would greatly help. Thanks Steve

AaronGTR
08-10-2011, 03:18 PM
Are you absolutely sure you are getting fuel? Because they had a problem with the fuel pump/sending unit in the tank up through '02 where it wouldn't restart when hot. You'd have to let them cool off before they'd start again. I went through two of those pumps myself before I got a revised unit. It would crank and crank but no fuel and no start.


As for the sensors, there are three of them that are required to operate the fuel injection and ignition timing. If there is a problem with any of them, the engine may continue to run, but it might not restart. Depends on the sensor and conditions. The big question is, is there a service engine light on and did you have the computer read for codes? And did you do it before trying to unplug the cam sensor? Knowing those trouble codes will go a long way toward telling you where the problem might be. That should always be your first step.

Anyway, the three sensors are the 24x crank sensor (behind the crank pulley), the7x crank sensor (on the back of the engine block), and the cam position sensor. A problem with any of those three will set a trouble code in the computer, and usually make the engine run in a default mode (aka "limp" mode).

All the signals go through the ignition control module (ICM) under the coils. The 24x crank sensor is used only for spark timing under 1600rpm. It has higher resolution so the timing control is better at low engine speeds. Above 1600 rpm, or if the 24x signal is lost, the computer uses only the 7x and cam sensor signals for timing. The ICM converts these to a 3x signal that goes to the computer. It starts out with a base timing of 10 degrees and a calculated injector timing pulse based on the last known. It looks for synchronization of the cam and 7x crank sensor to determine the position of the piston and intake valve in cylinder #1. It uses that to initiate sequential fuel injection timing, and also for spark timing control. If it loses either of those two sensors, the computer can't tell what position the crank shaft is in, and there by the piston or valve positions. So basically you have no timing control and it will run off the base 10 degrees, and no injector timing control. It's a V6 engine, so you have a 1 in 6 chance that the injector timing will be correct and it will start. If it's not in sync, the injectors won't be firing at the correct time and it won't start.

packman
08-10-2011, 04:27 PM
Wow thank you so much for the insight. I did have the fuel pump done last year by a very good family machanic. I actually had him try to look at the problem but he couldn't get it not to start until I went to go pick the car back up then he couldn't get it to start. He put a fuel gauge on it and the preasure was good but still no start. He checked spark and no spark. No service engine light no codes. If the crank sensor goes bad or going bad and the computer is relying on the 7x and the cam sensor for positioning would the car still start? It almost seems like when the car is hot the heat may be getting to the crank sensor allowing the car to keep running but unable to start while the engine is still at its peak running temp. until it cools down then the magnet it functional again. If this sounds like a possible senerio please let me know.