IAH Question

[Deeslfxr]

At what time during operation of truck does the IAH operate? Does it assist with cold start? Is it just for emissions purposes? Is it feasible/practical to rewire it to assist in cold start if it doesn't already? The truck in question is a '99 F-450 6spd with 220k on the clock. Any input will be appreciated! Thanx in advance!

[Southpaw]

It is only for reducing the amount of white smoke at idle. It has nothing to do with assisting in cold starts.

There are a few perameters to be met before it activates. Truck in Park, parking brake applied, ambient temp below a certain point(don't know what temp). There is 1 or 2 more I beleive, but thats all I can think of right now.

What issues are you having?

Sounds like you may be having problems with your Glow Plug system matbe.

[Deeslfxr]

Yea, I think my problem is pass. side UVC harness or glow plugs. I just replaced left four g/p along with installing harness wedge one month ago when left side unplugged itself. Also replaced IAH coil, found it broke when I removed intake tube to do right side g/p and harness wedge, except I never got that far. The guys needed the truck back so I buttoned it up and sent it out. It still starts hard when it gets cold out. I had to start it Wed. afternoon, approx. 15*F out, and when it finally started it shook and shuddered like half the motor was missing. I had my test light hooked to output of g/p relay to verify connection and while it was sitting there idling I checked to see if it was requesting the IAH or not, and it never did, even after the engine went into hi-idle. After it sat and idled for 10 min. or so I went out to move it and it was running fine. I figure it's time to finish the job and do the right side g/p and wedge. I was just curious as to the IAH's actual purpose and if it would better serve as an assist to cold start. I guess I was suprised a little when it still was not requested when the truck went into hi-idle. Thanx for the response Southpaw.

[Southpaw]

What were testing? the signal from the PCM side of the AIH realy? That is strange that it did not request it.

You said you checked the power output side of the GPR too, but never said if it was fine. I guess it was right?

[Deeslfxr]

Originally Posted by Southpaw

What were testing? the signal from the PCM side of the AIH realy? That is strange that it did not request it.

You said you checked the power output side of the GPR too, but never said if it was fine. I guess it was right?

Yes G/P relay was fine. I have not yet checked voltage drop across the relay or amp draw, just verified presence of voltage. I had battery voltage at both sides of the IAH relay (small pins) and it is my understanding the PCM switches the ground side of the IAH relay so either the PCM is not requesting it or the wire is open somewhere. I have not checked operation with my scantool yet so I'm not sure which is the case.

[Southpaw]

I would make sure you're getting around 11 volts on the output side of the GPR. It still sounds to me like the GPR. It is about the easiest thing to check too.