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12 - The Battery has been disconnected Within the Last 50 Key Starts.

14 - Map Sensor Circuit - Map Sensor voltage is low or high. - If Map Voltage = Map Vacuum but Map Vacuum is low (below 15"HG @ idle) you will need to determine why engine vacuum is low.
Do not forget that you have other components that are connected to engine vacuum that may have internal leaks such as the Brake Booster, Cruise Servo, Climate Control...
If you cannot locate the cause of the low vacuum you will need to run a Compression Test and a Cylinder Leakdown Test to be sure the issue is not internal engine related.
A compression test shows the engines ability to Build pressure.
A Cylinder Leakdown Test shows the engines ability to Hold pressure.
Both have to be done to ensure a complete and accurate diagnosis.
SPECS-Engine Compression.jpg



22 - Coolant Temp Sensor Voltage High or Low - This code is set from you checking/setting ignition timing and having the CTS disconnected with the engine running.

41/47 - Alternator Field Circuit Not Switching Properly/Charging Voltage Low
(6) 88-89 Charging Diagnostics 4.jpg (6) 88-89 Charging Diagnostics 5.jpg

54 - Fuel Sync Signal Missing/Erratic
Be sure the HEP connectors are clean/secure, the wiring for the HEP is not bent/damaged and that the Shutter Wheel in the distributor is not loose and there is no excessive lateral play in the distributor shaft.
 

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Discussion Starter #22
Holy cow the last few weeks have been a mess...went to vegas the week right before this Corona crap hit, came back and got promoted only to have everyone sent to work from home and then spent the last week and a half trying to figure out how to manage 10 guys out of my garage office. ugh but back to car stuff......

So I went through all the vacuum lines and was able to get the MAP fault to go away, every thing is pretty steady now at 17" (when the engine isnt' backfiring like an SOB. I'm down to the alternator fault 41 and the HEP 54 (which I still don't understand) The alternator is legitimately an alternator/circuit problem not an issue with the controller reading it. I can't get the car to read higher than 12.2 on my meter when running. Unhooked the main alternator wire and it reads 33vdc on the alternator stud??? WTF... Bench tested the old one that I took off and I can't get it to put out any voltage. So I believe the new alternator I got is junk.

As far as the HEP I really have no idea. Its a brand new sensor, that fixed the initial no start issue. NOS OEM. I've checked all connections, O-scoped all the signals which read fine and tested all the wiring back to the controller with no issues found. Dizzy shaft doesn't seem to have play.

I'll be honest, the second I can get this thing running on it's own without backfiring and falling on it's face it's getting sent down the road. it's almost summer and this thing is in the garage where my corvette should be. I just want this thing running and out of my life. And if it's not running good come next month, it's still getting sent down the road. I just don't have the time anymore.
 

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Discussion Starter #23
OH! another important detail I noticed. So this car is completely running like crap, backfiring like crazy and the RPMs are bouncing like a kid who had too much sugar. But when I hold the brake pedal down and put it in gear....smooth...the RPM needle is steady as a rock and it doesn't backfire! start moving (I took it up and down the driveway) and it's back to it's normal self, backfiring like automatic gun fire and will barely stay running.

not sure if that helps as a symptom
 

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A faulty brake booster will create issues, disconnect and plug the vacuum line from the booster and see if it makes a difference.

Is the backfire coming from the intake or the exhaust?

The alternator issue, does this vehicle have a Nippendenso Alternator with a tin cover on the back side?
If so, your issue is probably worn brushes, common problem.

Disregard the Code 54 until the charging issue is resolved.
 

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Discussion Starter #25
Man you really had the lightbulb going off in my head when I read that brake booster comment. I ran right out to the garage. The problem is this car doesn’t have a big vacuum brake booster it has that fancy TEEVEES brake system and I don’t see a vacuum line going to it anywhere nor is one shown on the vacuum diagram.
270154


as far as the alternator goes it’s an AC Delco style and it’s freshly factory rebuilt so I can’t imagine the brushes are worn.
270155
 

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The smooths out/stops backfiring when the brake is applied and the car is in gear has me baffled.
The unit is self contained, the only thing that comes to mind is an electrical issue (short?) the ABS circuit that is no longer shorted when the brake is applied.

Since you are having other electrical issues (Not charging, Code 54) lets focus on the not charging issue first as it may be related to the other issues you are having.

Sending diagnostics through PM.
 

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The smooths out/stops backfiring when the brake is applied and the car is in gear has me baffled.
The unit is self contained, the only thing that comes to mind is an electrical issue (short?) the ABS circuit that is no longer shorted when the brake is applied.

Since you are having other electrical issues (Not charging, Code 54) lets focus on the not charging issue first as it may be related to the other issues you are having.

Sending diagnostics through PM.
IIRC, the fuses for the Teves ABS unit are a bank of three fuses on the right side frame rail. You could maybe try pulling the fuses and see if this changes how the car runs. I agree with NAJ, this is very unusual. These cars are notorious for having the Teves brake problems. Lets hope after you get this engine driveability issue sorted out, that you actually have brakes so you can drive the car. The tell tale sign is a rock hard brake pedal. Feels exactly like no brakes. The Teves fuseholders are famous for burning up from bad connections on these cars. They will actually melt the fuseholder from all the heat generated by the bad connection.
 

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Discussion Starter #28
Well.... I think you solved another issue I was having without me asking....

I had to rebuild the entire brake system on this car. New calipers, rotors, ABS sensors, I bent all new hard lines and replaced literally everything downstream of the master cylinder. All new. I had bled the damn thing about 4 times now. The other day when my buddy was over to help me the main reason was to bleed brakes. (I figured if I'm gonna sell it running like shit at least I could say it stops good) well after 3 hrs of pheumatic, vacuum and the old school press press crack the bleeder methods, the brakes were still barely there. Service manual was clear as mud for bleeding them and it wasn't going anywhere so I gave up.

after reading your last post here at 10:30 PM I jumped out of bed and ran out to the garage. Broke that old brittle fuse holder cover getting it off, but there was one fuse missing towards the back. I replaced it. (looks liek the middle one meted at some point and they put an inline on in. well now when I key on I can actually hear that brake system fire up, and when I put it in gear and drive it back and forth I can actually hold it with the brakes. Still running like death but it wasn't back firing at least tonight, just wouldn't run without my foot on the gas. I'll try backing it out tomorrow and see how it feels.

thanks for the brake fix at least, hopefully.
 
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