Engine codes

Csirny

Registered User
I need some help with engine codes.
Here's what I've got

1990 SC

51
Engine coolant temperature sensor signal voltage is too high.

- which one is this? I've replaced the one that turns on the fan recently because the fan wouldn't turn on

54
Air charge temperature sensor signal voltage too high

- I replaced this one a few years ago the other one had broken.

56
Mass air flow sensor voltage signal too high

- I tried cleaning the MAF with a residue free electronics cleaner.
 
How does it run? What's going on that made you run the codes? Just the fan issue? Is it ok now? Did those codes exist before you replaced the ECT sensor?
 
It runs well. It was overheating do to the fan not running. I did have a previous problem with the dis module and the car would randomly buck/missfire. I replaced that and added an aluminum heat sink to the bottom of it along with arctic silver compound. This fixed that problem. And the dis ran cooler when I checked it with an IR temperature gun. The check engine light comes on and off while driving. The only running issue I'm currently having is an erratic idle randomly. It will jump up to 1800-2000 then slowly down to normal. I'm assuming this would be a bad IAC valve. The other problem I'm currently experiencing is a very noticeable hesitation after I drive for a while then step on the gas.
 
How does it run? What's going on that made you run the codes? Just the fan issue? Is it ok now? Did those codes exist before you replaced the ECT sensor?
I had originally ran codes do to the DIS problem. Then again after I repaired it because the check engine light was still on. I had less codes in the system after that but I think all the ones I listed were on both times.
 
You listed those codes ascending - what order were they when read? What is the first code reported when testing now?
 
I'm not sure. I'll check in the morning and report back in the order. I never thought to consider that.
 
I'm not sure. I'll check in the morning and report back in the order. I never thought to consider that.

Reason why is you should work the first code first - it may have an effect on the others and you don't want to waste time chasing ghosts/throwing money at the problem, etc.
 
The codes are in order. Tbirdjkc's post shows the temp and air charge sensor wired on the same circuit. Where would you start on this? Can I check resistance on these to see if there functioning properly? I did have a ground problem last year with the DIS because I powder coated all of my accessories brackets which put the car into a default setting. I was able to correct that code by adding a ground wire to the module. Could this be a similar issue with these sensors? Both my intake tubing and thermostat housing, and intake manifold are also coated. The air charge sensor does come in plastic or metal leaving me to think I may want to start with the coolant sensor. I believe the one for the fan to be working properly. After that how would you go about trouble shooting the MAF?
 
Hummmm...could be similar, as it seems odd those would all fail and throw codes at the same time.

Start by seeing which ones rely on ground and then start checking resistance.

Inspect the front/upper harnesses to see if they've been patched/damaged/oil soaked etc.

How does the car start and run with the MAF disconnected?
 
I'll check how it runs with the MAF disconnected and check OHMs on the coolant and air charge sensor then get back on that.
 
I'll check how it runs with the MAF disconnected and check OHMs on the coolant and air charge sensor then get back on that.

I believe you'd want to see resistance between sensor and negative battery terminal at less than 5 ohms.
 
OK. Just got back from a test drive. I drove into town and back home until the car started acting up (about 15 miles) with the car still running and it was at a higher idle (approximately 1600rpm) I unplugged the MAF. The engine speed then dropped to around 1000 then held pretty much around 1200 while driving. During Norma driving with the MAF unplugged the car felt slightly jerky. Kinda like pulling a trailer. And the throttle seemed a little hesitant but no where as bad as when the car is acting up with the MAF plugged in. I did however only drive about 2 - 3 miles with it unplugged. To describe the hesitation I'm having with the MAF plugged in (and it's random. Seems to clear up for a little bit if I floor it in a high gear like 4 o5 when I should be in 2nd) it's like this. With the clutch pushed in and I rev the engine it will read about 5 psi of boost with no change to the engine speed for a second or two. Then the rpms will jump up to Mach the position of the throttle. I'm going to check OHMs on the other sensors now and report back.
Thanks for the help so far also l. Really appreciate it. I was at a loss where to even start with this problem.
 
I unplugged the MAF. The engine speed then dropped to around 1000 then held pretty much around 1200 while driving. During Norma driving with the MAF unplugged the car felt slightly jerky. Kinda like pulling a trailer. And the throttle seemed a little hesitant but no where as bad as when the car is acting up with the MAF plugged in.

With the MAF unplugged, the EEC should substitute timing, spark and fuel defaults so the engine should still start, run and drive.

I'm starting to wonder if the EEC itself isn't having issues. Have you confirmed voltage at the battery when running somewhere above 12.2?
 
Temp sensor looks good. The air charge sensor doesn't read anything it has two prongs and I checked it every way I could. 1 side and - bat terminal. Other side and - terminal. And between the two.
 
Temp sensor looks good. The air charge sensor doesn't read anything it has two prongs and I checked it every way I could. 1 side and - bat terminal. Other side and - terminal. And between the two.

If a sensor doesn't rely on grounds, that's a different topic - to test just the ECT sensor:
  • Unplug the harness/connector
  • Check the signal voltage at the connector with the key on, engine off. Should be approximately 5.0v
  • Next check the resistance of the sensor cold. Should be between 58,750 ~ 40,500 ohms
  • Reconnect the harness and run the engine to normal operating temperature
  • Then unplug and check the resistance of the sensor hot. Should be 3,600 ~ 1,840 ohms

I had an issue one time where one of the wires in the connector had moved upwards and wasn't touching/grabbing the terminal on the sensor. Ended up replacing the connector.

Has the EEC been messed with?

Do you have another to test with?

Is the ground wire for the EEC connected at the header panel in front of the battery?
 
Last edited:
Good afternoon

In addition to the above suggestions I would check the "mystery ground" to the harness. It attaches to rear to the driver side cylinder head. Check for corrosion and or security.

Good Luck.
 
The ground on the back of the head I hooked up after doing head gaskets but I will double check that it's not corroded. The temp sensor is at 1,840 OHMs. The car is still pretty warm I'll check for a change when it cools down more. Still nothing out of the air charge sensor. Is it safe to assume this one is bad? Voltage at the harness for the air charge was 4.6 and for the temp sensor it was 5.6.
 
Back
Top