Engine/Transmission (1998.5 - 2002) Grid Heater Testing Procedure?

[klaybus]

OK..... Had a loose grid heater wire about 1 month ago. Tightened them up & all was well. Earlier in the week I was having a small hard start problem when truck was COLD. (start & die. Crank 5-6 sec & would start & run)

I thought perhaps a small air leak in fuel system so I filled the truck up & started truck cold again... Seemed to be better but still had a slight hiccup upon a COLD start. VERY small hiccup, but a hiccup none the less. I haven't started the truck for 36 hours or so & left the trucks block heater plugged in & came home tonite & truck fired right up, IMMEDIATELY! NO HICCUP what so ever... The vlltage guage drops when I'm waiting for the wait to start go off but what I'm thinking is I might only have one grid heater working.

Does anyone have the testing procedure for the grid heaters. Nothing in the service manual. It refers to the powertrain diagnostics manual.



Thanks,

Clay

 

[klaybus]

bump to top.

 

[DavidC]

Ok, I will try this,Ohmmeter required. I just read across mine and from each terminal on right side(from relays) battery to ground I read. 4 Ohms. that is for the intake grid. Still looking to ohm fuel heater although its power is fuse 7 (40 amp) at PDC. Probably going to have to pull Fuel heater relay in PDC to get a resistance reading on that one. I'll be back. I did not want you to think no one hears you.



Dave

 

[DavidC]

Well, apparently the fuel heater has a built in thermistor type system and since my system is warm I have an open across the element. The fuel heater is energized from the Ignition switch with no apparent control other than the ignition being enabled. The fuel heater has internal control to close when cold enough. This being the case you could just have a bad relay. 85 to 86 is the coil and ohms at 76 on the relay.



Dave

 

[SS]

You could test the relays to see if they are even providing voltage to the heaters.



I just removed both relays from the fender well and cleaned all of the connections - it's not a bad job, just takes a little patience. Not sure mine needed it, but good preventative maintenance anyway.



Steve

 

[klaybus]

This morning I checked both relay outputs & had 12V at the grid heaters. I cycled them twice to verify voltage & they both were getting 12V. I replaced my leaking fuel filter canister today while changing the oil so we'll see if it was a small air leak in the fuel system tomorrow.



Clay

 

[DavidC]

Did both grids ohm out ok?. Just for future people that come across this thread later. Just an FYI. , It is good to know you have voltage at the heaters but that in it self does not verify operation. If the circuit is not complete (open heating element(s), bad ground etc. ) you can have voltage with no current flow. Another check would be with a clamp DC amp meter around the grid power wire to verify current flow. These grid heaters can pull upwards of 95 amps DC. Do not use the little 10 amp section most meters have on them. As for the fuel heater it has a variable temp controller that regulates the resistance of that heater that starts around the fuel being 45 degrees or less. The resistance varies from 0 to 1000 ohms depending on temperature. The fuel heater relay is energized from the ignition switch during the start/run cycle. This means the relay is energizedall the time that the key is on. If the fuel heater is calling for heat (45 and below) it will warm the fuel. If the internal sensor should become defective while the key is on the fuel heater will eventually become toast (warm fuzzy feeling huh). I want to thank Clay for bringing this subject up as I have learned alot with component locations and operation. At least when and if I have a problem I will be more familiar with its operation.



Dave

 

[klaybus]

Too warm outside to try to get readings by myself. By the time I would get from the cab to the meter they would be shutting off. I'll have to get some help or wait until it gets colder outside.



Clay

 

[DavidC]

Clay,

I have a way around that if you want to try it. Each grid heater relay has a coil of its own. One coil is a yellow/black the other Orange/black. These come from the ECM. Remove these wires from the relays and isolate them. Using a jumper wire (with alligator clips preferred) connect one end to one of the relay coils that you removed the ECM wire from (making sure it does not contact any grounded metal part of the relay) and the other end to a 12vdc source (Batt. etc. ) a 5 amp fuse link spliced into this jumper would be nice just in case it would contact ground at some point. this way you could test the individual grids. I would not leave it jumpered for to long tho. Just enough to verify it is working. Then test the other. These wire colors are for a 99 vehicle. If you feel skiddish about this do not do it.



Dave

 

[klaybus]

Clay,

I have a way around that if you want to try it. Each grid heater relay has a coil of its own. One coil is a yellow/black the other Orange/black. These come from the ECM. Remove these wires from the relays and isolate them. Using a jumper wire (with alligator clips preferred) connect one end to one of the relay coils that you removed the ECM wire from (making sure it does not contact any grounded metal part of the relay) and the other end to a 12vdc source (Batt. etc. ) a 5 amp fuse link spliced into this jumper would be nice just in case it would contact ground at some point. this way you could test the individual grids. I would not leave it jumpered for to long tho. Just enough to verify it is working. Then test the other. These wire colors are for a 99 vehicle. If you feel skiddish about this do not do it.



Dave

Dave,

Essentially I'm just un-hooking the ECM wire that triggers the relay to power the grid heaters individually? This would allow me to check the Amperage draw to verify that the individual grids are working -vs- just checking 12V being present? Is this correct?



Thanks,

Clay



PS... . Truck started fine this morning

 

[DavidC]

Yes, It checks everything except the wire and signal from the ECM, you are essentially bypassing that part.



Dave

 

[DavidC]

Any update?.



Dave

 

[klaybus]

Weathers been lousy so I've been hiding indoors. Truck started fine this morning so I'm thinking small air leak fixed with new FF housing. Will test later in the week if the weather improves.



Clay

 

[DavidC]

2:10PM, 60 degrees and sunny. You can rib me this summer when it is 115 and sunny while your at 80 :-laf .



Dave

 

[klaybus]

41*, overcast with light rain . Just checked the weather in Palm Desert & it's 71* & sunny! :{ I gotta get outta here! In about 5-6 months we'll see some of that 70* weather if we survive the winter & spring soakin of Seattle!



Clay

 

[radar doctor]

Good Article For Refference... . thanks For Sharing Tech Info... doc

 

[klaybus]

Still stumbling & dying on DEAD COLD start

Dave,

38* today & truck stumbled again! Frick! Going to have the wife help me tomorrow do your test procedure. Hopefully I can get some closure to this problem... .



Clay

 

[DavidC]

Another thing to consider is the crank position sensor. It usually sets a code tho and the CEL. It will cause a stumble tho. The IAT sensor determines when and how long the grid heaters operate. The fuel heater as stated before is internally controlled. Have you scanned for any codes?. There is no real test that I know of with an intermittent cps, when Mine was acting up it would only seem to do it at on ramps with an up hill grade. When I removed it the sensor was a little scuffed up on the end.



Dave

 

[klaybus]

Codes....

No I haven't. I've done the CPS before & last time that went I got the CEL. I'll run over to my brothers house & use his Smarty & verify I'm code free...



Clay

 

[klaybus]

Did a little metering tonite

OK..... It's friggin cold in the Seattle area so I did some metering tonite. Here are my results.



Batts with truck off read 150 A DC

Batts at idle read 190 A DC @ batts with no grid heaters cycling

Batts at idle read 155 - 165 A DC @ batts with grid heaters on

At each grid heater individually I read 140-150 A DC with truck running



Dave,

Was I reading the meter correctly? You had mentioned about 95 A DC but I read considerably higher. I did not unhook the PCM triggering them I just grounded the meter & took the readings from the grid heater post & also from the battery. From these results it tells me they are working correctly. What do you think?



Clay