hard starting 5.7 2003 crusader mpi

Engine starts fine when cold but a few minutes after shutdown will not start unless given about 1/4 throttle if engine is hot or cold. Replaced pressure regulated and had injectors tested for leaks but no leaks. Have seen threads with same issues but not any solutions. Engine runs fine but occasionally do have slight fuel smell.

maybe your temp sensor(s) are out of tolerance....some would say 'inaccurate'....try a scanner or get the service manual and use a digital meter (resistance measurements).

Thanks for the suggestion makomark. Just pulled the boat for the season yesterday but will check temp sensors in the spring.

lwr said:

Thanks for the suggestion makomark. Just pulled the boat for the season yesterday but will check temp sensors in the spring.

Click to expand...

Still having problem starting engine after running even for very short time and still cold. Will only start if given a little throttle. Had reputable mechanic check with scan tool and he found no problems or codes. Starts right up initially when cold but require throttle after run even for short period. Also have fuel smell occasionally after running at low speed for awhile .

If it will not start unless you crack the throttle is sounds like the IAC valve (idle air control) is not adjusting. Question is has the valve failed or is it not being told correctly what to do. If the scan shows "no problems" it is likely the valve. If you have another engine it is an easy swap of the valve to see if the problem moves. If you don't, then you will need an MEFI-4 diagnostic manual (you can find on the internet...see my past posts) to gain an understanding of the system and devise some tests to try and nail the problem without the use of a scanner. If the IAC is working it is constantly adjusting the idle speed to hold 650, no matter if the engine is cold or hot. Does it do that? Can you partially cover the throttle body hole and will it adjust to hold idle speed?

As I recall the manual also explains how to take the valve apart and inspect and service without damaging it. Good to read.

Here is a sample:
Idle Air Control (IAC) Valve
The purpose of the IAC valve assembly (Figures 3-7 and 3-8) is to control engine idle speed, while preventing stalls due to changes in engine load.
The IAC valve, mounted to the throttle body, controls bypass air around the throttle plates (Figure 3-7). By moving a conical valve known as a pintle, IN, towards the seat (to decrease air flow); or OUT, away from the seat (to increase air flow), a controlled amount of air moves around the throttle plates. If RPM is too low, more air is bypassed around the throttle plates to increase it. If RPM is too high, less air is bypassed around the throttle plates to decrease it.
The ECM moves the IAC valve in small steps. These can be monitored by scan tool test equipment, which plugs into the Data Link Connector (DLC).
During idle, the proper position of the IAC valve is calculated by the ECM, based on battery voltage, coolant temperature and engine RPM. If the RPM drops below specification and the throttle plates are closed, the ECM senses a near stall condition and calculates a new valve position to prevent stalling.

Engine idle speed is a function of total air flow into the engine based on IAC valve pintle position plus throttle plates opening.


•

“Controlled” idle speed is programmed into the ECM, which determines the correct IAC valve pintle position to maintain the desired idle speed for all engine operating conditions and loads.



As good as the manual is, it will usually give you 2 or 3 other possible causes for any problem so don't get too fixed on the first logical idea.

Sorry, my "sample" did not come though as clear as expected. Better get a manual!