89 idle issue

[Leadfoot33]

my dads 93 LT1 had an issue where it would barely idle, had to clean out the IAC sensor/valve. not sure if the L98 has the same but id assume so and start there.

 

[theboss]

Hi Steve. About your low voltage, get someone in the car, pu t it in drive, take a voltmeter and take a reading directly at the big wire at the alternator, very often I see .2 or more difference, make sure you groud the voltemeter on the alternator housing. Next, still with your meter grounded on the alternator check the voltage at the battery (car still on drive), the difference might be around .1 volt. If idle is to low, alternator wont charge as much. Do this test at normal operating temp. If I would have to check this car, i would clean mass air flow, throttle body and if your car is equip with a IAC motor, I would remove it to be clean + the passages. Next would to check for vacuum leaks. Make sure you do a good road test after cleaning, left over of cleaner can enrich the mixture and fool you on the result.
I am away from the shop and no access to shopkey website, I will get back to you next week.

Good luck

Stephane

 

[Steve Fontaine]

ive also found a piece of info that interests me. i was looking up possible causes on google and one forum post with the same issue said that his gas filler cap was clogged and creating a vacuum.

not sure why this didnt come to my mind before but my gas tank creates a crazy vacuum after driving for a bit. in fact the vacuum is so crazy that i literally park the car overnight and fill it in the morning. thats the only time i can fuel it up without there being a vacuum.

the guy also said that taking the cap apart and cleaning the clog fixed his problem.

also as stephane mentions, i have a feeling there are things in this vette that need cleaning. the guy that owned it before only put 4000km on it in 10 years. and it basically sat around for the rest of the time. he did have the basic maintenance done and i have all the records from when it was first bought by the original owner. i didnt see anything in the history about any real cleaning of things. just general tire stuff and oil changes.

ill check the gas cap when i get a chance later today.

 

[Steve Fontaine]

ive also have gone through the paperwork for the vette. seems as though it hasnt really been serviced since 2008.

so therefore rather than risking driving it anywhere (not that i have been),, i am going to park it and do some work on it from now on. better to have a vette that works and just need a bit of fixing than to drive it until its dead. theres no way ill ever to be able to afford another vette so im dam well going to take care of this one.

i guess i will start by cleaning the exterior and protecting it. cleaning the interior and protecting it. then i will move towards the engine and clean the crap out of it inside and out. ive only just noticed the engine bay is very dirty. cant imagine whats build up inside the engine. ill also be replacing whatever needs replacing. i want to also polish up and make the engine all shiny and snazzy. like a show car. right now it looks like its been sitting outside in the weather for 10 years.

not sure what ill do with the paint. has aa touch of sun damage and has a few chips on the front. also has those light scratches from people washing it like a donkey would. that drives me nuts.

so this will probably be the start of a video series on bringing an 89 vette up to car show quality.

i dont like things that dont work right. it drives me nuts. and i will fix them come hell or high water

let the fun begin...... tomorrow morning

 

[Rruuff Day]

We will be following along Steve.

 

[Black 03 Z06]

Steve, no doubt you will accomplish your goals. Great to have you here to post the technical issues that I am sure you are not alone with.

Good luck to you and as Eric says we will be following along.

 

[Steve Fontaine]

Before i start this journey, is there anyone in edmonton who has a code reader that will work on an 89?

 

[ddgermann]

I have this one. Should work on 90s and up.
I will be home 1 day on the 26th before I head to work. You can pick it up and use it if you want.

Product Detail

Derek

 

[Riley P]

Is it still OBD-1? You may be able to read the codes by putting a jumper wire between pin A and B and reading the check engine light flashes.

How to read older GM OBD diagnostic codes for free

 

[ddgermann]

Is it still OBD-1? You may be able to read the codes by putting a jumper wire between pin A and B and reading the check engine light flashes.

How to read older GM OBD diagnostic codes for free

Yes apparently it does.

"Does the Scan Tool work on OBD1 vehicles?
Yes. The Scan Tool will work on selected OBD1 vehicles (Ford, GM, Chrysler and Toyota). In order to read OBD1 vehicles, OBD1 adapter kit 3129 is required. You also have the option to purchase the adapters individually. To view the adapters you will need to select your model number tool under OBD 2 diagnostic tools and click on the accessories tab."

This was a pretty decent reader when I bought it a few years ago to diagnose an wheel sensor on my 13 Z06.
Ended up putting on a new hub.... lol could have saved the money as the reader couldn't change the hub. ?!?!

D

Oh just read what I posted... "adaptor".
Doh!

This 89 corvette should be OBD2 no? Steve?

 

[Steve Fontaine]

i had heard about this paper clip things before but was skeptical. Turns out even a code reader for OBD1 reader does mostly the same thing as a bloody paperclip does. it makes the engine light blink...... glad I used a paperclip and saved myself another bunch of $$$

to get the code definitions i went and downloaded the manual for a GM OBD1 reader for the vettes correct year. again saved $$$$

im gunna take my hat off to stephane.... the only code coming up after 12 was.......

CODE 36 DEFINITION BELOW

-Mass air flow (MAF) sensor - burn-off circuit problem

-Transmission shift problem (electronically controlled
transmissions only)

-Direct ignition system (DIS) fault - loss of 24X signal or
extra or missing pulses in electronic spark timing (EST)
signal

-Ignition system fault - loss of High Resolution Pulse
signal

the others seem to be sub issues of code 36 from what i can tell. but im pretty sure its the mass air flow. that engine is DIRTY. i dont have time to go take it apart now and the battery went pretty low getting the code. i sat there for 10 minutes and also had the radio going without the car running. so of course it turns over and sputters out.

ill make videos as soon as i can but it may be a few days. work is stupid busy lately.

 

[Steve Fontaine]

i also just realized the burnoff circuit is a different part. anyhoo.... ill be checking that and replacing as needed.

im glad parts for this vette are all over the place

 

[Steve Fontaine]

Also just found this gem of information.

Most of the C4 Corvettes used a MAF (Mass Air Flow) sensor to determine how much air is being pulled into the intake manifold. The exceptions are the 1984 Corvette that used a speed density system--a sort of predictive method of measurement---and the 1990 through 1993 C4 models which were also speed density based. In 1994, Corvette went back to the MAF based system but used the speed density approach as a back up. (1989 Bosch MAF installation shown at right).

A Mass Air Flow sensor has an extremely fine wire inside its bore. The 1985 through 1989 C4 engines used a Bosch MAF sensor that heated the wire to 100 C. The 1994 and later C4 models used a AC/Delco MAF that heated the wire to 200 C. The amount of current required to reach the temperature is measured in each case. (Note: the LT-5 engine used in the ZR-1 used a speed density system and continued to use that system in 1994 and 1995 since the engines had already been made prior to the last two years of production. The ZR-1 therefore has no MAF even after Corvette went back to the MAF based system).

Theory of Operation

As the air travels past the heated wire enroute to the intake manifold, it will cool the wire and additional current is added to again heat the wire to the design temperature. Since the amount of air moving past the sensor is directly related to the amount of cooling experienced by the heated wire, a feedback condition is established whereby the exact amount of moving air is directly related to the amount of current passing through the wire and the intake air is therefore precisely measured.

Once the amount of air is known, the computer controlling the engine can add or subtract fuel as required to maintain the magic 14.7:1 air-fuel mixture resulting in the cleanest burn possible from an emissions (pollution) standpoint.

It does this by varying the "on time" of the fuel injectors. The injectors are pulsed on and off and the width of the pulse is lengthened or shortened as required. When you first start a typical engine, the pulse width is around 4 milliseconds but as soon as the engine "catches" the pulse width is shortened to about 2.2 milliseconds for idle. During operation, the measured air flow through the MAF will cause the computer to increase or decrease the pulse width as explained above.

MAF Operating Conditions

The Bosch MAF is more complex than the AC/Delco version. Both measure the air flow but the Bosch MAF has a circuit called the 'burn-off circuit' that cycles on for about 2 seconds when you shut the engine down. This circuit heats the wire to a high enough temperature to burn off any residue that may have collected on the wire during operation. If you are in a quiet area, you can hear the relays click on and then off on a 1985-1989 C4 as the burn-off cycle occurs.

​

There are two relays involved with the Bosch MAF: A power relay that passes current to the MAF wire during normal operation and the burn-off relay that provides the current for the cleaning cycle. Both are located on the firewall in the engine compartment, just behind the battery on the drivers side. Bad MAF power and burn-off relays can cause hard starting problems and should be changed periodically as preventative measure and any time you experience hard starting conditions.

The AC/Delco MAF has a power relay but no burn-off relay. For this reason, you should pay even closer attention to the condition of your air filter on a later model C4 than normal since a contaminated wire in a AC/Delco MAF is going to stay contaminated for the most part and cause false signals to be passed to the computer.

Also, the Bosch MAF outputs its information as a analog signal to the computer but the AC/Delco sends its signal as a digital component of varying frequency. For this reason, you cannot measure it's operation directly.

A scan tool is generally the best way to troubleshoot engine problems and with the 1994 and later Corvette, it is virtually mandatory. (An oscilloscope will also work on the AC/Delco MAF but a regular test meter will not).

MAF Problems

Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

MAF Mods

The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter.

i like the bolded red part best

 

[Steve Fontaine]

Ok guys, i need help with this one.... i cleaned the MAF sensor and the vette started without problem. the idle is steady and the battery is better but not perfect. ill get to that later.

after driving it around the block and letting it idle a bit. i gave it a few revs. now i noticed before a bit of smoke coming from under the hood after being driven a few times. but not all the time. after testing out the clean sensor...... i noticed the source of the smoke. this one is beyond me. exhaust, oil leak, i have no idea but i do have a dam clear video of the source and its a good thing i was recording so you guys can see.

i hope this isnt a major thing. im getting tired of doing nothing but fixing it.

 

[Steve Fontaine]

ive taken a closer look and its coming from part of the exhaust pipes. possibly when i went over a bump in the road and smacked the underside. i do remember that happening once. and i cringed when it happened. but what is leaking out of the pipe and is it safe to drive till it gets patched? it only does it when i hammer the throttle or rev it up a lot. or drive like a 13 year old in grand theft auto. (joking.... its more like a 20 year old)

 

[Steve Fontaine]

well i took it out for a quick gentle drive to see if cleaning the sensor kept up its gusto. and a big fail. that and the leak under the vette now has it doing the same things as before. rough idle, dropping battery voltage. smoke from underneath. so im gunna park it and save money over the winter.

 

[theboss]

I wonder if the catalytic converter is partially block, this could get you a low vacuum (rough, pour idle) and get real hot when you hammer it. Hard to see if it only smoke because of temperature or if a liquid is leaking on it.

 

[Steve Fontaine]

I wonder if the catalytic converter is partially block, this could get you a low vacuum (rough, pour idle) and get real hot when you hammer it. Hard to see if it only smoke because of temperature or if a liquid is leaking on it.

im going to take a bit of a break. trouble shooting this vette for half the summer is getting tedious. when i come back, ill have a more HD video. but please feel free to send thoughts on this issue. i will still follow this thread.

 

[ddgermann]

I wonder if the catalytic converter is partially block, this could get you a low vacuum (rough, pour idle) and get real hot when you hammer it. Hard to see if it only smoke because of temperature or if a liquid is leaking on it.

That's actually a pretty clever thought.
Makes good sense. There seemed to be quite a bit of smoke in that leak. Like somethings burning....

 

[MikeysZ06]

im going to take a bit of a break. trouble shooting this vette for half the summer is getting tedious.

Yeah,stepping back might be a good idea. I think most of us can sense your frustration Steve. Myself,I would've given up in July. Sure give you an "atta boy" though for your perseverance.