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1985 Laser XE
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Discussion Starter #1
Hey guys, had a number of seals and gaskets, as well as the clutch replaced in my '85 Laser, and since then, it's been idling weird (revving to 2300 by itself while traveling around 40mph with the clutch pushed in, or let out. It feels very much like the cruise is set when it does it. If I brake to slow the car, engine speed slows at about the same rate as wheel speed, finally settling to normal idle speed when the wheels come to a complete stop. This, to me, points to the communication between the transmission speed sensor, the logic module, and the IAS. It's a debate in my own mind whether the speed sensor was messed with during the transmission work and is now 'confused', or if the logic module & IAS didn't appreciate the loss of battery power and can't figure out what to do when the car is moving. This isn't a constant thing....it does it once or twice during a drive, and then won't do it the rest of the trip. It didn't do it at all on my 19 mile commute from work on Friday.

Today I discovered the cooling fan and A/C are not working. This failure seems to point to the fan relay, as the fan runs when powered directly with 12V, but doesn't run when I jump the temp switch plug (ignition on).

With these failures all coming on the heels of repairs that included the battery being disconnected, I'm beginning to suspect that the shop wasn't careful when messing with the battery connections, and allowed it to arc, possibly providing a surge to delicate electronics. Is this a reasonable conclusion, or am I out in the weeds?

Ordered a logic module, speed sensor, and fan relay, and it appears I'll have to be satisfied with just cleaning the IAS, as there isn't one on the planet that doesn't currently reside in the throttle body it's always been in (wrecking yards). I've read through the service manual, and it offered two ways to test the cooling fan, and then points to the relay. I thought about just ordering a relay, but if it's more than that, it's more waiting for more parts to ship, so I rather just wipe out all possibilities at once, if that makes any sense.

Anyone else experienced this weirdness after a battery disconnect?
 

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The pull through Turbos (84-87) are infamous for having erratic idle issues. Here is a link to Chromguy that cleans the AIS motor. I've cleaned four of them now and they all work great again.
 

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Speed distance sensor can give idle speed issues.

High idle that drops when the vehicle stops is a common one.

I usually commit blasphemy and set the crew your not supposed to touch.

I don't allow the AIS to control idle speed, prefer solid stable, reliable idle.

Very few agree but that's normal for me!!.

Thanks
Randy
 

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1985 Laser XE
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Discussion Starter #4
The pull through Turbos (84-87) are infamous for having erratic idle issues. Here is a link to Chromguy that cleans the AIS motor. I've cleaned four of them now and they all work great again.
This looks about as much fun as rebuilding a Fiero headlight motor. I did that, I guess I can attempt this. What's the type of failure these typically experience? Dirt buildup preventing the mechanism from moving? It looks fairly foolproof, unless the motor doesn't run. Can you just remove the motor and soak the valve assembly & planetary gears in a plastic-friendly solvent, rather than disassembling? I try not to take stuff apart if I don't have to. :) I ruined my power seat switch a couple weeks ago, so I'm gun shy.
 

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Before disconnecting the battery or after driving are any fault codes set?

Is this the reason you are ordering/replacing your engine controllers?
 

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1985 Laser XE
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Discussion Starter #6
I don't know how long the codes have been there, but when I checked it a few nights ago, it had 12 (recently lost power), 25 (IAS) and 34 (EGR Solenoid). I'm replacing the Logic Module in case the IAS & Speed sensor aren't the problem. The speed sensor concerns me because I'm sure they either removed it, or unplugged it when working on the transmission. The Logic Module is last thing I'll replace if the IAS cleaning and speed sensor replacement doesn't fix the idle issue. If those two things fix it, I'll have a spare Logic Module, which I'm fine with.

As far as the EGR, I read that even if it sticks open or shut, that doesn't cause high idle, so it's low on the priority list. I can't find any broken vacuum lines, as that's definitely a suspect after valve cover gasket and timing belt work. If it did have a vacuum leak, wouldn't it idle high all the time? When the car is sitting still, it idles at 900 or so. Occasionally, it struggles to idle and drops to 600 or so, then it suddenly clears up and goes back to 900. Engine speed doesn't really get screwed up until you top 40mph, then it sticks at 2300 and drops in conjunction with wheel speed when I brake, settling at 900 once the wheels fully stop. This is why a vacuum leak doesn't seem plausible (to me).

Thoughts? I don't mind replacing stuff, but if you think the issue lies elsewhere, please feel free to share. I'm the newb.
 

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The problem with replacing the controller before diagnosing/repairing is that you are using a remanufactured unit that may or may not be 100% reliable and cause other issues.
Do not send you OE unit back before all of these issues are corrected.
1)Code 12 is normal after battery or controller power disconnect.
2)Code 25 - Follow the advice given about the AIS and see where that leads.
3)Code 15 - Does your speedometer work?
Clear the codes, drive the vehicle and see if any codes return, then you know they are true faults.
PM being sent.
 

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Discussion Starter #8 (Edited)
Speedo works. This is the other reason I included replacing the LM. It's uncanny that all these electrical issues surfaced after the battery had been disconnected. I can't rule out the possibility that a surge / arc affected 1 or more components. Irratic idle and no cooling fan all at the same time.....fishy.
If the speed sensor and IAS are ok, it pretty much has to be the brain of the operation at fault, no?

I had no intention of sending the original back. They can keep the core charge.

How do you clear codes? Unhook the battery?
 

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if your car drives like it's on cruise control .. you also want to check for a short between terminals on the logic module in the kick panel

I had one with a cowel leak above it .. when washing the car it would drive home at 50 KPH without my foot on the peddle

fixing the leak and warping the top of the computer & it's plugs with plastic solved it
 

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suck through style turbos can also have run away throttle if the hoses between the throttle body / turbo / intake manifold , have a hole in them
 

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1985 Laser XE
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Discussion Starter #11
The problem with replacing the controller before diagnosing/repairing is that you are using a remanufactured unit that may or may not be 100% reliable and cause other issues.
Do not send you OE unit back before all of these issues are corrected.
1)Code 12 is normal after battery or controller power disconnect.
2)Code 25 - Follow the advice given about the AIS and see where that leads.
3)Code 15 - Does your speedometer work?
Clear the codes, drive the vehicle and see if any codes return, then you know they are true faults.
PM being sent.
Unhooked the battery for 40 minutes, then took it for a drive. Only went 1.8 miles but got it up to 50mph. Not a sign of the runaway train I experienced this morning driving the same speeds. For the moment, can't drive it much further away because I never now how far it's gonna get before it overheats. It only set code 12. Fan relay is supposed to get here Friday. It's pretty much hobbled until then.
 

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Keep us posted on the issues discussed above and any others that may arise.
 

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Discussion Starter #13
Replaced the coolant temp sensor on the thermostat housing. Made no difference. No fan.
 

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I did not know we were working on a cooling fan issue.
The CTS (coolant temp sensor" only supplies coolant temp info to the controller, the controller in turn actuates the fan relay when temps reach the appropriate point.

START by verifying you have power in and out of Fuse #6 (Back Up Lights/Radiator Fan)
If OK...

Backprobe the CTS connector with a digital voltmeter and watch the voltage(voltage translates to an actual temp).
1)Does the engine reach proper operating temperature according to CTS voltage?
(This is important, disregard the gauge in the car)
2)If Yes, did the cooling fan cycle on at the appropriate temp?
3)If No, with the engine running disconnect the CTS connector, this puts the car in failure mode which brings timing to base and cycles the cooling fan on.
4)With the CTS disconnected check to see if you have power on the Lt.GN (Light Green) wire at the cooling fan connector.
5)If Yes, check the fan motor ground, be sure you have continuity to ground on the BK (Black) wire at the cooling fan connector, if OK, replace the cooling fan motor.
6)If no, diagnose the cooling fan relay circuit.
The relay circuit has two power feeds, ground side control of the relays pull in circuit and an output to the cooling fan.
1)Gray Wire - Constant battery power through a fusible link
2)White Wire - Switched ignition voltage thru FUSE #6.
3)Dark Blue/Pink Wire - Ground side control from Cavity 21 of the LM Red Connector.
4)Light Green - Output to cooling fan motor.
(The other two wires at the relay are A/C related)

Backprobing The CTS
Backprobing the CTS.JPG CTS VOLTAGE CHART 2.jpg 85-87 LM Turbo Red.jpg
 

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1985 Laser XE
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Discussion Starter #15
Thanks for the detailed diagnosis info. I will be tackling this over the weekend. Right after I bought the car, I noted several occasions of the fan coming on while idling in the driveway. Up until this week, the temp gauge never passed the center square.

It appears the cooling fan started failing to come on sometime after I got it back from the shop for the gaskets / clutch. Thinking back, it didn't overheat on the drive from the shop to my office (about 5 miles), or the 19 mile drive home from work. It did get a little warm (according to the gauge) picking up takeout the next day, but it didn't last long. I discovered then that the A/C also does not engage.

I attempted to return it to the shop early Tuesday morning for something unrelated, and it overheated 4 miles from the house in 30 degree weather. I noticed the gauge near H, and made an immediate turn into a subdivision and killed the engine as the verbal warning started. I didn't hear any loud ticking, nor any coolant boiling noises. I let it cool for 45 minutes and drove it home. The gauge reached 1 square past the middle by the time I got home.

Since then, I've run a 12V lead directly to the fan to confirm it runs. I've pulled the temp sensor plug while running, and got nothing. I've idled it in the garage twice in the last two nights, and observed the temp gauge passing the middle square, with no fan kicking on. I've confirmed that the radiator and overflow are filled, and observed that the radiator and heater hoses get very firm and hot.

I'll dive into your instructions tomorrow. I really appreciate you putting that together.
 

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1985 Laser XE
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Discussion Starter #16
Using my analog voltmeter, I have around 2.3 volts coming from the temperature sensor, stone cold engine. The gray wire at the relay is not showing any voltage, ignition on or off. White wire shows 12 volts with ignition on. Ignition on, when I unplug the temperature sensor, I get a click from the relay. Light green wire at the relay is getting no voltage when I do this.

Bad fuseable link?
 

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Discussion Starter #17 (Edited)
Tracing the path of the gray wire, I found that it goes into the wrapped bundle headed for the firewall, but a few inches down, it comes back out of the bundle and heads back toward the battery. It has one of those smash splicers on the end of it, and whatever it was connected to broke off. Can you tell me what it's supposed to connect to? I can't find an orphan anywhere down by the battery.
273349




273350
 

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Discussion Starter #18
Never had any luck finding what this wire used to be connected to, so I spliced it into the emergency flasher lead coming off the battery. Everything running cool now, including the A/C.

Thanks for all the help guys.
 
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