el ohmbre

I have no Check Engine Light on an 86 Corvette with the ignition on and engine not running. The car idles OK in Park but stumbles and stalls once it's put into gear. When idling, there is a noticeable hesitation when the gas pedal is pushed before the rpms increase. I'm thinking there is a code but no check engine light means I can't read the code.

WVZR-1

Find someone with a 'scanner' or maybe check for burnt out bulb or missing bulb - 3 solutions!

kael

Also check basic #2, fuel via fuel rail pressure through the port on it's passenger side. Just at key on, no start, it should jump up to 35 - 40 psi within a couple of seconds and stay for a bit, 15-20 minutes, at key off. If that's good, should be somewhere in 30s when running. If not, fuel pump or filter may be an issue.

Oh, as far a check engine light, do the simple paperclip check, it should give a code 12 at least, that's the okay code.

383vett

I don't know where you are located, but it may be hard for you to smog your car if that light doesn't light up.

aklim

Sooner or later, you would need a scanner. That will tell you way more than a code. It would go better if you put your location down in your profile so people can see if they can lend you a scanner or not.

Could be fuel or spark. HAve you checked to see if the plug wires are leaking? Are the plugs good? How is the cap and rotor? What is the fuel pressure with the hose removed and engine running? Does it hold pressure after shutdown? Once we know that, perhaps we can suggest something else.

c4cruiser

Could be as simple as the bulb is burned out. Any chance you would be able to drive the car to one of the chain auto parts stores like AutoZone, O'Reilly's or similar? These stores will hook up a scan tool to the OBD port and pull any codes for you.

Then post the codes here.

el ohmbre

Thank you everyone for the suggestions. I found someone with a scanner. I sort of assumed that if the light wasn't working, I couldn't get the codes but with a scanner, I should be able to see what's going on. I'll post the results when I get a chance to run the test.

I did check the ECM fuse and it's good and has power. I tried to follow the shop manual and probe Terminal A5 on the ECM connector, but I'm embarrassed to say that I couldn't find it. The ECM is under the dash above the passenger's feet, right? I removed the lower panel but still didn't get a good look. I might need to remove the seat. I will check the light bulb too. That is probably a little more accessible.

The plugs and wires are new. The timing looks OK but the mark was a little rusty and hard to read. I'll mark it with chalk and test it again to make sure. The rotor and cap are good. The engine runs fine at higher rpms, even under load. It's just at low rpms and in gear where there's a bad problem. It wants to hesitate and then respond but likes to stall.

Yeah, I'm in California and I need to pass smog to get it registered. It was a mess under the hood. Couple of things disconnected, like the MAF sensor. I cleaned up the electrical connections and plugged them back in. Several vacuum hoses disconnected which I reattached.

I will see what I need to check the fuel rail pressure as suggested.

Paperclip test doesn't work because there is no Check Engine Light to flash the code. Although I did try it.

Thanks again everyone. I'll post the results of the scan.

aklim

I'll be blunt. I'm guessing the previous owner tried to fix it by pulling the MAF offline and the check engine light was removed to hide it. ECM would notice the MAF was out and run it off the preprogrammed tables Sounds like a hack job of a repair attempt that they gave up on and sold it to someone with the Corvette Fever.

Buy yourself an FSM and a scanner You are going to need both. Buy a fuel pressure tester or borrow one first.

el ohmbre

LOL, Blunt is OK. Maybe there is a nice way to say "hack job" because that is exactly what this car is. It was used as some sort of "test bed" by some engineers. It hasn't been registered or driven for years. I'm trying to get it going again.

Based on the comments here, I suspect the Check Engine light is either burned out from being on continuously or it's disconnected.

What is an FSM?

aklim

Factory Shop Manual. It is year specific and it is NOT a Haynes or something else. For most, it is very useful. In your case, mandatory since you have no clue what the Previous Owner, aka liar, moron, etc has done. https://www.ebay.com/itm/1986-Chevy-...FZtxwQ&vxp=mtr

Thing is, the scanner will get you things that the Check Engine Light doesn't tell you. For instance, if it is 70 degrees outside but your ECM sees -20, it is plausible but incorrect. If you see on the scanner it says -20, you know that the CTS is either disconnected or wrong although it doesn't show up as a CEL. Scanner can tell you codes and data. Code checker is an expensive glorified paper clip at best. So even if you can read that there are no codes, it might not be accurate.

Kevova

With the car history you need the previously suggest factory service manuals not a Haynes or Chilton manual. Also car was built with obd1 which was used prior to 1996 model year. You will want a scanner with the correct cartridges and accessories to read car. Not all OBD2 scanners will read OBD1 cars.

el ohmbre

OK, got it. I have the Factory Shop Manual. I just didn't recognize the acronym.

I know the history of the car a little bit. It was used by some GM engineers as a test bed, so they messed up a few things during their testing, mostly electrical. At some point it got parked and abandoned except for a few amateur mechanics who tried to get it running but mostly broke more things than they fixed, mostly mechanical.

I think the scanner I can borrow is for OBD1 but I'll verify that before attempting to use it.

WVZR-1

Get 'brand and model' of the scanner. If it happens to be a GM Tech1 it would require a 'specialty adapter' to do '86 thru '89 TPI and it seems there were maybe issues with very early '86 cars.

***A 'quick check for ECM' might be considered a jumper A - B of the ALDL. If all's well the COOLING FAN should 'turn on'. It by no means is a diagnostic you're looking for but quite likely a quick check. Have you noticed the fan turn on when you've attempted a check even though you have NO LIGHT?

el ohmbre

I was finally able to borrow a scanner today. It is a SnapOn MT2500.

I connected it to the ALCL per the instructions. It asked a couple of questions and then asked for a few digits of the VIN which resulted in the correct car. I got a message that it was waiting and asked me to turn the car on. After a few moments I got a message that said: "No Data" and a suggestion to check Appendix B in the SnapOn MT2500 manual. I tried it a few more times with the same result going through the process in a slightly different order. Then I tried driving it a couple of miles and testing again with the same result.

Appendix B had several suggestions. The applicable section was: "Engine runs but runs poorly." This section suggested checking the Check Engine Light, (which is what started this thread) and checking the ALDL.

Is the ALCL and the AlDL the same thing?

Since I have no Check Engine Light, I'm assuming it's on the same display near where the Security and Low Coolant lights are located. It looks like a little LCD screen. Are there separate lights behind that panel?

Kevova

There is a diagnostic chart for check engine light. You may want to confirm ecm is present and the correct part number. Knowing was type of modifications the engineers were working on could be helpful.

aklim

There should be a module in the scanner Is it correct? I suspect so but thought I'd mention Also, did you have to connect power to the plug? Some do

WVZR-1

You mention probing A5 but unable to reach. I don't believe you need to go all the way to the ECM. This image isn't from an '86 FSM but it ID's C238 and and it's more easily reached. First as silly as it sounds you need to be sure INJ1 fuse is not blown, that powers all of the 'TELLTALE' lights I believe. Check your FSM.

Terminal B in that connector should be BRN/WHT - I'd think you could check it there. If fuse is good and you've nothing with the test light there's either a blown bulb, no bulb or a problem in the circuit. Look in your FSM 8A-20-2 maybe to confirm my thoughts. Depending upon manuals used it's safe to assume ALCL & ALDL are same!

el ohmbre

The ECM is present. I'm not sure which is the part number but here are the numbers on the case: Serv. No. 1227165 below that is has 869701 M513368449. Are any of those the Part number?

The engineers were building and testing a Heads Up Display to display the dash gauges on the windshield while driving. Something they did causes a 3.3 amp drain on the battery when the car is off. Therefore they installed a "knife" switch on the negative battery terminal to completely shut down the car. I have figured out that the courtesy lights stay on all the time. I pulled the courtesy light/clock fuse and the current draw dropped to 0.01. I left the negative cable connected last night with the courtesy light fuse removed and it was OK.

There are two modules installed in the scanner GM, Chrysler, Ford, Primary and GM Chrysler Ford Troubleshooting. The mechanic I borrowed it from thought these were correct. Yes, I did have to connect a separate power cable.

It probably would have been easier to probe at C238 but using a mirror it was pretty easy to drop the ECM. I wanted to look at the part numbers anyway. I had a bit of trouble figuring out the orientation of the connector based on the picture in the shop manual but the color of the wires helped me to get oriented.

Now, I'm afraid I screwed up big time. I was following the troubleshoot steps and "back probing" A5 at the ECM. Looks like I had 12v on A6 and ground on A5 which points to an open circuit or bad bulb. I must have somehow jumped two pins with the probe because there was a distinct click inside the ECM and the cooling fan which had been running shut off. (Someone had asked if the cooling fan was on with the ignition and it was.)

I tried to start the car, it started and then immediately died. I tried it a couple more times and it wouldn't start and I could smell gas. I let it sit, it started then died. I really hope I didn't do something terrible. I disconnect the battery ground, let it sit and got the same results.

So, it appears I'm moving backward. Did I kill the ECM?

el ohmbre

Looks like I blew the fuse on the ECM. I'll replace it and report the results.

aklim

If you blow the ECM fuse, how would you smell gas? Should be no injector pulse Would it even crank?