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Topic: Gremlins (Read 2075 times) previous topic - next topic

Gremlins

okay guys, here's one for you.. ive got 30 yrs exp with cars and its got me confused!!! my guages dont read properly and car idles slightly rough... but when i turn on the headlights guages read closer to proper and car runs alot better!!! ive replaced all cables...check alt output....even added 2 more grounds.. its not digital dash..im wondering if ecm is ping out??? car is a 88 5.0 xr7 fully loaded.:mad:

Gremlins

Reply #1 –
Is your radio original or aftermarket? Any other mods?
CoogarXR : 1985 Cougar XR-7

Gremlins

Reply #2 –
i see where your going it does have a sony cd player, but shouldnt affect way car runs maybe guages but wouldnt wiring need to shorted somehow...

Gremlins

Reply #5 –
Well the gauges are fairly simple!!! Is the CVT ok??? I call it the constant voltage regulator. It can be found on the back of the cluster as FOE pointed out. With a proper ground and a good IVR that should solve the cluster issue. But wait you said the car runs better with the head lights on?? I had an issue with this some time back with a PONTIAC!!! What happened in this case was the ALT was sending out NOISE. When i turned on some loads the car stopped missing. So i would check for NOISE on the electrical side of the charging system. This can be dun with a SCOPE. Stranger things have happened. If the ALT is putting out noise it will some times make the ECM GO NUTS!!!. I know this is a long shot but disconnect the alt from the car and drive it with the BATTERY. If you loose the symptoms you found your issue. When ECM'S found there way in to CARS YEARS BACK NOISE was an issue. And alternators were designed with less NOISE to not foul up the ecm by producing NOISE. That is where i would start. Along with voltage drop readings and also drops across the battery and ground sides of the charging and battery systems. Also check for stray EFI from the ignition system sometimes it can effect the ECM as well. Just a long shot!! Good Luck!!
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

Gremlins

Reply #6 –
thnx guys i will check those this weekend....also have another dumb question....whats the diff between the gt40 heads and the gt40p heads...pick apart near me has tons of exploders with the gt40p heads and they are cheap!!!! 35.00 each head...plus the intakes are like 80.00...

Gremlins

Reply #7 –
trinom the guages read higher with lights on ...

Gremlins

Reply #8 –
GT40 heads are on 96 and early 97 Explorer, they feature internal EGR as does the Explorer intake for the same, also the valves are bigger than stock HO heads as are the ports . After that the GT40p heads have a unique spark plug angle that requires special headers and the exhaust valve is smaller (same size as E7TE heads), they have a different chamber shape, and the intake that matches them requires heavier modification to be adapted to our cars due to a number of small differences.

Personally, I like the earlier heads better, although some argue that the p heads make up for the smaller exhaust valve with their better chamber.  Either way, you'll want an HO cam and you'll want to use an early intake with the early heads, and the late intake with the P heads.

Gremlins

Reply #9 –
Quote from: 88Merc50;420079
trinom the guages read higher with lights on ...
That's weird. Dead IVR causes, that gauges read higher.

Tom, it can't be called constant voltage regulator, just because it's function. It is self heated bimetal switch, which oscillates with some frequency. It turns on and off the voltage to the gauges. 5V means, that it is 5/14 of the periode on and the rest off. It's very inacurate and I don't have a clue, why they decided to use this piece of  instead of semiconductor voltage regulator.