a3dcadman

iTrader: (1)

Ive been in the process of installing, setting up, tweaking and troubleshooting my newly rebuilt engine. One of the problems I had was with the engine getting very hot, at least it seemed that way. My aftermarket gauge was reading 250F+ and the stock gauge was not working as it needed a new sending unit. After doing everything possible to the cooling system and still dealing with a 250F reading, Rynberg suggested that maybe there was a gauge error. Thats what it turned out to be.

The gauge had worked just fine just before pulling the engine and I typically ran at about 190F. So, I bought another gauge with its included sending unit. Installed it and ran the engine. The new gauge is reading up the scale and goes all the way to 250F maximum reading. The stock gauge which Ive fixed is reading center scale.

What would cause this behavior in the temp gauge and could it affect my other electrical components water temp sensor, air temp sensor, fuel temp sensor etc. I am 99.9% sure that Ive assembled everything right, adjusted all idle control elements right, and replaced with new, all components related to idle control, but I still have the erratic idling, surging and rich running problems.

chuck

Mazda99Nikon

What is the standard limits for voltage and amperage coming off the battery and alternator? So many people seem to report these sort of problems. I can recall a thread I read recently where someone simply cleaned the terminals of his battery and dispensed with all his freaky idle problems.

See Berker's post: https://www.rx7club.com/showthread.p...cal+load+stall

DaleClark

iTrader: (55)

OK, let me sort out a few things here. If you start the car in the driveway and let it idle, the temps will creep up until the gauge pegs out? Do the fans kick on, etc?

I'm wondering if you have some fundamental timing problem, like plug wires swapped or something - that'll definitely cause poor running and potential overheating.

What kind of gauge are you running? Where is it tapped into on the cooling system?

The stock sender for the gauge on the dash is it's own system. The wire from the stock sender goes straight to the dash - it doesn't interface with any other system.

Dale

a3dcadman

iTrader: (1)

The engine gets to about 190F while idling and the fans dont come on. I can engage the fans with a switch I have installed which is connnected to the loose female spade terminal behind the ecu and high speed by pushing AC button. The engine has been burped and is using no coolant and is not over-heating.

The gauge upon start up almost immediately starts to register temperature and gets to 250F before the stock gauge shows any temp reading at all. The sending unit is on the front face of the thermostat housing on the small circular flat face next to the low coolant sensor. The gauge used to stay at the cool end of the scale until the thermostat started to open and then would come up to operating temp relatively quickly.

Gauge is an Autometer 3337.

When I am at cruising speed on the highway, the car seems to perform fine with the exception of zero boost which I am still troubleshooting. Idle seems to stabilize under load, placing tranny in reverse or drive. My first priority is to isolate and rectify my idle surging and rich running issues. I had to take out 38% of fuel at idle so car would idle and not pop, sputter, and backfire. This is one of the reasons I was thinking that the sensors are reading off scale just like the temp sending unit.

chuck

scotty305

iTrader: (2)

1.) First I'd verify that your Autometer gauge is working properly. Have you tested the autometer in a controlled environment? If you dunk your sensor in a pot of boiling water, and your gauge should read ~212F, right?


2a.) Next, check that you're seeing similar results in your car. When cold, my car's coolant is about 60-80F, depending on ambient temp. I'm not familiar with that autometer gauge, what is the lowest temp it will display? From a cold start, it should take at least 3 minutes of idling for the car to warm up to 140-160F.


2b.) I've built a digital temperature display to replace our innacurate stock temp gauge, and can send you more info about the coolant sensor on the rear iron than you would want to know. You could measure the OEM sensor's resistance with a multimeter and get a pretty good idea of how hot your engine is. If you send me a PM with your email address, I'll send you some resistance vs. temperature tables.


3.) How many wires are running between the Autometer sensor and the gauge? It's possible that your Autometer sensor is relying on the engine for grounding. Seeing how you've recently R&R'd the engine, it's possible that your engine grounding points aren't making a good electrical connection.



-s-

a3dcadman

iTrader: (1)

Scotty,
I am going to take the gauge I replaced and do a bench test with it and the sending unit today to see what temps are registered. When I first figured that my temp gauge was giving the wrong temperature, I used a kitchen thermometer in my coolant to determine that my coolant temp was 60-70F under what the gauge was showing. Gauge registers 100F - 250F.

pm'd you for temp vs resistance data.

The gauge has one wire that goes to the sending unit, one wire that powers the light bulb, a12v power connection and a ground. I have the gauge grounded to a connection under the dash. The sending unit is relying on the thermo housing for its ground.

If the grounding to the engine is not adequate then could the other sensors be affected as well causing the erratic idling characteristics Im seeing? Is the aftermarket temp sending unit is a thermistor type sensor where temperature affects the resistance and therefore the reading and are the oem water temp sensor and intake air temp sensor of the same variety? If so, then would the resistance data sent to the ecu be wrong and therefore cause the ecu to compensate by adding more fuel when its not needed?

Thanks,
chuck

scotty305

iTrader: (2)

Emailed you the data.


Since your Autometer gauge is relying on the engine grounding, I'd say you've got a problem with your engine ground. Hold one side of a wire on the thermostat housing, and the other side to the negative battery terminal; if your Autometer gauge shows a different temperature with the extra ground wire, then that's a pretty sure sign that your engine ground isn't working properly.

If your engine isn't properly grounded, it's very likely that could be causing your idle problems. The ECU would be doing weird things with the ISC valve if the coolant temp sensor is sending it the wrong signals.

-s-