1985 bogs down & bucks like a horse

[gmhowe]

my 85 bogs down and bucks like a horse while cold when I hit 24-2600 rpm in every gear. but if I drive for 4-5 miles shut it off. wait for 30 seconds start it up and it runs file.. I have stumped the dealer and a couple of vette shops here. it is a manual tranny. have replaced almost all sensors plus the MAF.. major frustration here since no one seems able to help......

 

[Eagle85C4]

Have they plugged into your ECM to see if the signaling and values are right?
Have you checked the fuel pressure?
Have you checked the fuel regulator?
Have you checked the EGR valve?

 

[gmhowe]

New egr, new fuel pressure regulator set at 37 lbs, new ECM same proms, new o2, knock, tps, iac, maf, esc sensors, fuel pump, fuel filter, distributor cap & rotor, plugs and wires.

 

[BlackNBlue95]

my 85 bogs down and bucks like a horse while cold when I hit 24-2600 rpm in every gear. but if I drive for 4-5 miles shut it off. wait for 30 seconds start it up and it runs file.. I have stumped the dealer and a couple of vette shops here. it is a manual tranny. have replaced almost all sensors plus the MAF.. major frustration here since no one seems able to help......

It only bogs at around 24-2600 RPM when cold? does it go away once it warms up while driving? or muct you shut it down and start it up again and the problem is gone? just trying to figure out the sythom a little better to see if I can come up with some suggestions..

 

[gmhowe]

Yes, if i keep driving it all day it will still bog down between 24-2600 rpm, i if stop after 4-5 miles and turn the engine off and wait for a minute or so it runs fine with no problems.

 

[BlackNBlue95]

Yes, if i keep driving it all day it will still bog down between 24-2600 rpm, i if stop after 4-5 miles and turn the engine off and wait for a minute or so it runs fine with no problems.

OK.. so after you shut it down and wait a minute and start it up and the problem goes away then when does the problem re-occur? after it sits and cools? or the next say after it sits overnight? or does it just start happening after driving it a while? It sounds like something computer related.. but I'm not shure.. it's hard to diagnose a car over the internet.. but I will try to see if we can find some direction on this..
-Rick

 

[gmhowe]

Every day when first driving it, if it cools down after shutting it down and it runs on, yes it starts up again with the same thing, I have a new computer but the old proms.

 

[Zektor]

Hi,
You say it bogs down in every gear. Does it bog down whether you give it hard full throttle or not. So, if you gently bring the engine up to that speed does it do it then?

Also, if you bring the car to a complete halt, and rev it up when standing still... is there a noticeable difference?

Lastly, when you've shut it down and restarted after a minute... are you absolutely sure it does not do it at all?

Cheers
Dazza

 

[gmhowe]

If I jump on it when its cold it immediately bogs down, if I do it slowly as soon as it hits 2400 rpm you can feel it start to bog and when it does I shift.

After I shut it down and restart I can jump on it and no problems.

reving it up there is nuthin noticeable whether cold or not.

 

[tntcorvette]

is the car throwing any codes? I noticed you did not replace the maf sensor burn off relay....its located somewhere behind the crash pad........

 

[gmhowe]

The only code I get is 21 stating the TPS is too high, I have kept setting it down, Its not at .440 . Did not replace the relay, I guess I could try that, Hell I've replaced just about everything else.

 

[tntcorvette]

in that case i'de double check the wiring to the tps with a fine tooth comb. check for correct voltage from the ecm to the sensor before you spend major money on a new relay.

You can sometimes find a used relay on ebay or such.


good luck.

 

[gmhowe]

one thing I noticed at a stop lite today, while still in the cold mode
if i step on the gas in neutral and rev it up to 2500 rpm and hold it the engine lopes. uhhh uhhh uhhh ( hows that for a description)

 

[vee93]

'85 bog down reply

In regards to:
1985 bogs down & bucks like a horse

my 85 bogs down and bucks like a horse while cold when I hit 24-2600 rpm in every gear. but if I drive for 4-5 miles shut it off. wait for 30 seconds start it up and it runs file.. I have stumped the dealer and a couple of vette shops here. it is a manual tranny. have replaced almost all sensors plus the MAF.. major frustration here since no one seems able to help......
--------------------------------------------------------------------------------------------------My '93 was doing this. Like the gas was bad or moisture was in the gas...
No codes on the car appeared, diagnostics were good, BUT!!!
I hate to tell you this if you're not an "engine head" who can tackle the job yourself, a $1400+ tune-up solved the problem.

 

[tntcorvette]

this one has me stumped....definetly something to do with cold temp. running conditions....so when the car warms up it runs fine, right?

Off the top of my head, only the egr/egr wire to egr valve/cold start injector/chip/computer/o2 play a role in cold temp operations.

And since you have checked everything and get a code 21 re: tps sensor ide say its something simple, yet hard to find.

Mabey its mechanical??? Valvetrain, distributor????

 

[BigRed]

Have you checked the injectors? I know you have done pretty much everything up to them but have you actually checked them?

Another thing is throttle body cleansing?

Could the old prom be doing this as well?

 

[BlackNBlue95]

Re: '85 bog down reply

In regards to:
1985 bogs down & bucks like a horse
My '93 was doing this. Like the gas was bad or moisture was in the gas...
No codes on the car appeared, diagnostics were good, BUT!!!
I hate to tell you this if you're not an "engine head" who can tackle the job yourself, a $1400+ tune-up solved the problem.

Bad gas can happen.. actually we had an 85 vette in that wouldn't start.. we found that it had water in the gas.. when we went to check the fuel pressure it was good.. but when we went to check fuel volume we noticed kinda a milky fluid withthe gas.. we were going to run the tank dry and fill it with some fresh gas and stable to help get rid of the moisture.. anyhow I couldn't remmber where the fuel pump prime connector was on those.. so I told my co-worker.. it's easy enough to take the gas door off and cover and the top of the tank is righ there so I went to show him and we found that because this vette sat outside it had collected leaves under the gas door which clogged the water drain which caused the water to get into the tank somehow even with the has cap on (it was on at the time)

anyway bad gas can happen but i would seriously fix the TPS problem first and see what happens.. say you have a dead spot on your TPS (not saying this is the problem) and you at 25% throttle or whatever and you hit the dead spot not it either thinks its all the way open or closed or doesn't have a signal so it can cause it to stummble, buck, bog down what ever.. basically I would fix that first.. it's a key feed back sensor...

 

[vigman]

Could be bad grounds

Check the wiring from the negative terminal of the battery to the frame ground... then the frame to the block connection points... then the harness grounds to the block.


Search for my post "Getting Grounded"

Vig!