I've got an AutoXray scanner and when I scan the ALDL all the readings seem to be accurate except:

1.) Coolant temp is always between 238*-257* no matter what the dash guage reads (ie: LO, 150*, etc.). Even when the car has sat overnight.

2.) TPS voltage is .54v but wide open it only reads up to 1.31v. I did a manual check of the TPS with my voltmeter and it reads 4.65v wide open.

I was thinking the coolant temp could be the Coolant Temp Sensor. But now I'm thinking it might be the ECM itself. I used to get a consistent code 33 but since replacing the TPS that has not come back in a couple of months. But now I still get the same symptoms that I used to get with the 33 (cutting out at part throttle) but no code.

I used the scanner on a friends car and the temp was the same as the guage, so I know the scanner is ok.

Also, I don't know if this is related but, the car is suuuuppppper hard to start when it has sat for a few hours when temps are below 60* out. It cranks fine but won't start, then it starts to start but dies, then it finally starts. :boxing

I was supposed to put a new fuel pump in this past weekend but the part that was supposed to come in Friday didn't come in until Monday. :cuss

I'm lost :crazy: , what do you guys think?

TIA

 

Definately start with the CTS! When the engine is cold it thinks it's hot and it's not giving it enough gas like a bad choke on a carburetor. :seeya

 

The ECM reads the TPS, MAP and CTS sensors for start up to set idle. If there is a problem with the CTS or the way the ECM views the CTS, that might explain your hard start up problem. If you haven't replaced the CTS, get one from Koop..there cheap. You might just check the wires into the ECM from the CTS. If no problem and the sensor is OK..you might look at the ECM.

[Modified by ittlfly, 3:05 PM 11/20/2002]


[Modified by ittlfly, 3:10 PM 11/20/2002]


[Modified by ittlfly, 6:41 PM 11/20/2002]

 

Thanks a lot guys. I will check out the wiring, and probably just replace the sensor since it's only $12 at CSK. It's so amazing how all these pieces fit into this puzzle.

:cheers:

 

You can measure the resistance of the sensor (in the block under the TB) when cold and again when warm.

It should be near 100k Ohms cold and 1k Ohms or less when hot.

You might clean the TPS sensor and plug contacts with some tuner cleaner from Radio Shack.

You might also try the O2 sensor check (after you fix the coolant temp sensor issue) on my site.

If the other scanner readings seem OK I wouldn't suspect the ECM.

 

Had some odd readings and codes on my ECM (85) turned out to be a bad engine ground wire. On the 85 it is attached to the thermostat housing.

Good luck, hope you find it. :cheers:

 

I think you have bad connections, bad ground, or bad ecm.

89 original ecm's have board issues that cause these kind of problems, but many work for a long time with no problems. What does the ecm think the fuel pump voltage is?

You may have multiple issues. If you find that the ecm is bad, make sure you get the new updated part number for the 89. I used Jeff koop, don't trust a rebuild for an 89.

Good Luck

Pete

 

Vette boy I'm having the same problems with my '91. Does your car hesitate while you driving and under accelertion? Mine does. I got the aut x-ray and pulled a tps sensor. Replaced that and ran fine for a couple minutes. Then problems like before. Then the x-ray pulled the tps and map/maf codes. I was looking at real time data, and it looked like my coolant sensor was bad ranging from 58-120-230-58 degrees in an order like that over and over again at start-up. Car stalls alot too. I'm going to fool around with the coolant temp switch this week-end. Lets keep in touch so we can figure this out! Talk to you soon. Good luck :cheers:

 

Thanks for all the input guys, I will try these other suggestions this weekend (got "wife birthday duty" tonight). For now here's an update on what I did last night:

a.) Dash temp guage reads - 163*, engine has been off for about an hour.
1.) Scanned system, CT=244.5*.
2.) I pulled the plug on the CTS and plugged it into a new CTS but didn't put it into the engine, just left it in open air. I scanned it and CT was 113*.
3.) I pulled the old CTS and did the same test, CT=113*.
4.) Installed new CTS into engine and scanned, CT=244.5*.

I didn't get a chance to check the wiring, but I will do that next. To check the wiring I was thinking about connecting two wires directly to the ECM (C10 and ground) and the sensor, then run a scan, depending on the reading won't this help rule out wiring and determine whether it's actually the ECM?

My fuel pump voltage is 11.9v key on, but drops to 9.7v-10.7 while cranking the engine.

Topless91L98: My hesitation is while driving if I part throttle, it will dog out, like it's out of gas or has a dirty fuel filter or something like that. When it did this before it would throw a code 33 but now it doesn't throw any codes at all. While it's doing this if I floor it, it just won't go, but if I let off the gas and then hit it, it will go just fine. You can email me at ctrillo@earthlink.net, or IM me if they ever get that feature working again.

Thanks again guys, I appreciate your help. ;)

 

I would check all the grounds on the engine and the ECM harness. If that's all good then I would suspect the ECM.

 

Update:

I checked the wiring and couldn't find anything noteably wrong. So...

a.) Dash CT guage - 190*
1.) Scanned system, scanner read CT-244.8*, TPS open 1.31v
2.) Got new ECM and installed it.
3.) Scanned system, scanner read CT-188*, TPS open 4.61v
4.) Started and test drove car, ran fine.
5.) Let car sit overnight, scanned system this morning, CT-60* (dash-LO).
6.) The car started right up with no problem...WOOOHOOOO!
7.) Uh oh...SES light, code 32 :confused:
8.) Stopped at gas station, put gas, started car, no more code 32.
9.) Drove 62 miles to work, no codes, car ran great!

Thanks a million guys, I really appreciate all your help as usual!!! :thumbs:

 

I'm glad you figured it out! :cheers: