Roustabout

I am new here and I did not find my issue. I hope I'm loading in the right area, if not please forgive me


I have a 1994 C4 Corvette with an LT1 engine. It has 63000 miles on it.

I have one minor issue that comes and goes very randomly. It starts with a surging idle. And at low speeds under 60 miles an hour if you lightly step on the throttle it's kind of like it misses and falls on his face. Step on the throttle just a little harder to get the RPM's up it takes off like a scared rabbit. When all this is going on it will also begin pinging. It doesn't matter if you're running regular or super. At first only slow speed median pressure on throttle. it random I think it seems to be on a hotter day and a long drive. But not always.. it's very random..
As you continue driving the ping gets louder and more higher RPMs the surging at a idle is more . it seems the hesitation or stumbling or missing on light throttle seems now at lower RPMs and speed. Never seems act up above 60-65. My gas mileage is pretty consistent between 16 and 20 miles a gallon going back forth to work and normal driving which consists of Freeway in town.20 to 24 on a trip.

I have a tech 2 GM scanner,
No codes in the computer.
everything else seems to be going great in the data stream.
I have not been lucky enough to have a chance to put the scanner on when is acting up it always seems to be over with my time I'm home. Any help will be greatly appreciated.

thank you

Larry

VikingTrad3r

can you scan the car while its acting up and look at the long and shrtbterm fuel trim? with the ls engine swapped it may hard to get people here to help as few specialize in it.

id suggest renaming the title of your post to include "LS swapped " in it.

there are many of us who want to do ls swaps and a few who are doing them currently.

one day im sure we will have an ls swapped section in the c4!

what are your fuel trims saying while its acting up?

pcolt94

Some things I would check first:

Fuel pressure. Best to check while driving the car also.

Check vacuum hose for FPR to make sure no fuel is in it.

Clean or check throttle body.

Check the voltage swing of the TPS. Use your Tech 2 to see if the voltage swing is smooth with no drop outs from low to high. You can do this with the engine off and the voltages should be form about 0.6 to 4.5 volts. You can also do this with a basic volt meter back probing the connector. There should be no rough spots.

Do you have a FSM?

Roustabout

So far whatever I've been with the tech 2 the car is acting normal. Last night it acted up I rushed home. By time I had the tech 2 it was running normal. (It's the LT1)
I have been going to test the throttle position switch just didn't know the voltages thank you I will be checking that. FSM the factory service manual yes I have a set
Thank you guys so much for your input

itsalwayssomething

FWIW..Your fuel mileage seems pretty low compared to my 95. I'm averaging 25.5 MPG running a Procharger with shall we say "spirited driving".

pcolt94

The manual transmissions will get better mileage than the automatics. I have auto and indicate 25 on the digital readout on expressway. But a mix of driving and around town which is what the car sees these days, I really see somewhere around 20- 22 +/- depending on stop and go or a open road. Not right or wrong, those are just my numbers.

My fuel trim is right in the zone close to 128 on all short and long readings. You should make that measurement to see what it is. Best to do it while driving in a low cruise. This may not be your problem but a clue or data point of how the whole servo loop is operating with O2 sensors, injectors, PCM, fuel distribution and a bunch more inputs.

Does not sound like a fuel filter but how old is it or how many miles are on it? Never hurts to replace. If you want to service you car a real basic tool to have is a fuel pressure gauge.

Even though the engine runs good at times, there are still many check that can be made as I had indicated in my previous post. The more data recorded on a piece of paper gives you a reference point for later when the engine in acting up.

Roustabout

My car is an automatic. Yes my gas mileage I guess maybe a little low I've been pretty happy with it I think I may have got better last year. Fuel filter less than seven thousand miles ago. I've been thinking throttle position switch for a while I've got to do a few tests just looking for anything I might need a test at all this weekend. I work nights so generally anything I do on the car will be done on the weekends I will update thank you for all your help

Roustabout

After replacing the map sensor for 2 weeks the car ran unbelievable more power just overall perfect. Today I took a road trip car was running great until I gassed up after gassing up it seemed to be pinging again at first no real hesitation . As the day progressed it started to hesitate or Miss. It continued getting worse all day long it was 104 degrees out today and the car around 238 - 242 this is hotter than I remember, I believe. It got to where is missing so bad if I stepped on the throttle at all it just missed. long as I maintain the throttle down I can do 70 down the road. When I got home I let it set for 2 hours went out and started it doesn't seem to be missing like it was earlier, but it's pinging like hell. I picked up a new fuel filter last one was changed I think under a year again maybe I wrong. Hook up the techo 2.. everything went great except the oxygen sensors were jumping around a little bit on the numbers. Everything else looks solid andlook right.. I've never received the code yet from this issue or the computer

My friend with me today is convinced it is fuel-related. I think electronic. Could this be an opti ignition issue?

The car has about 66,000 miles on it.

Roustabout

I do not know how old the water pump is. I'm assuming Factory. Yesterday was 102 hour and today was 105. These are the worst two days I've ever had with the car. Last Summer no issues at all. I cleaned the MAF with the special spray for it. Made no difference. I unplugged maf as someone told me to try. other than getting an error in the computer made no difference. What I've noticed today over ever before is it seems to be pinging a lot. yesterday and today the hesitation seem more like a miss. the car starts running worse the temperature seems to beven rinning hottet. normally it runs around 200 maybe 209 on a hot day today.the last 2 is it going all the way up to 240 +. Just seems to be getting worse and worse. I was asked about the fuel filter I've just recently installed a new fuel filter in it . When scanned everything seems to be ok no codes coming up on the computer. no codes at all.

antfarmer2

Change the front two o2 sensors and hang on going to be a new car. It is running a bit hot pull the radiator and give it a good cleaning. Pull the knocks and give it a good flushing. I replaced my knocks torque is important 14 lb. Do not get your opti wet. Get the o2 socket from orielys use the short one pass side is a bit harder.

You have two problems first change the front o2s. Once you see it run better than ever. Then clean all the crap out of the radiator pull it and do it good. Since you have lost most of your coolant flush it you must pull the knocks to do it right. There is nothing wrong with them but I do not put back 20 year old parts that are that cheap. Pinch the connectors with your fingers to get them off. If you keep running it hot and get to 250 good chance you will blow your head gasket.

Roustabout

I will give the 02 s and then knocks a try on Sunday. Tomorrow Saturday is another 105 degree day. One thing I have found it set for a couple hours I took it for a drive ran 100% better until the temperature started coming up it went up to 210 -211 and that's what I started noticing it not running as well when hit 214 that started to miss or hesitation.. I will also change the thermostat. Should I change the water pump? The water pump is not making any noise and I see nothing coming out of the weep hole

pcolt94

After re-reading everything again and if you have done all the recommended checks, I think you have a bad optispark.

If there are no codes many times its just the cap. In the past I would replace the whole unit but now days its a crap shoot to get a good optical sensor in a new unit. Its a gamble deciding what direction to go. Cap or whole opti.

Roustabout

Okay $2,000 question. I called AutoZone I can get there opti the ignition with a lifetime warranty for just under $160. The Duralast brand any good? I think that's the brand AutoZone sells.

antfarmer2

I just added to my post if you want to put a new opti better start soaking the pulley now. I would rather you just fix it instead of tossing parts at it but if you do keep the old working opti I will buy it.

Roustabout

I am kind of at a loss what my next steps going to be at this point in time. I wish I knew a good mechanic in the Portland Oregon area that I could trust. But I honestly don't know says my mechanic retired quite a few years ago.
I think I'm going to change your O2 sensors first. And see what that gets me.

antfarmer2

If your going to own this car best advice is get a FSM and ask questions your doing fine. Now go get two o2 sensors and the socket and change to front two o2 sensors. Do the drivers side first to get your confidence up. youtube will give you a good idea what to do. If you have a friend at a oil change place buy him dinner and drinks.

Roustabout

I want to thank all you for all the wonderful advice. A friend of mine's give me a number of his mechanic. He works on Corvettes Trans Am I guess another performance cars.. He said he'd come over tomorrow and he knew what the issue was and he said $50 he will fix it. If he can do it for fifty bucks I'll be happy I will let everybody know what I find out. Thank you all again and I may be asking more questions thank you for being patient with a newbie

pcolt94

If you know how to use a Tech 2, then look at both O2 sensors and see if the voltages are swinging full range quickly. O2s can be sluggish (hard to evaluate) but still work OK. If they are a real problem, usually the gas mileage goes way down and a code could be set. They usually won't cause surging and the symptoms you have described.

I think if you change them you will get lighter in the wallet and have new O2s with same problems. IMO

Good luck with you new mechanic.

Silver96ce

Because of the pinging, I would check operation of the EGR system.

Roustabout

I think the o2s look right on the tech 2.. I am far from being good with that scanner. I understand the basics.
This went from a random thing that was just a little annoying real quickly to a major issue. It really seems heat-related. Hoping the gentleman I have coming over today is as good as I'm told he is fingers crossed. Thank you all for all your help it is majorly appreciated