"Parping" from 3500rpm up on secondaries...

[c4koh]

All,

Since yesterday, my 92 ZR1 has developed what I can only describe as a very resonant "parping" noise above 3500rpm, and only with the secondaries (full power) on. Power seems somewhat reduced, but the car is certainly quicker with the secondaries on than with the power key off. The sound sorts of bellows throughout the entire car, and sounds like it's not breathing / exhausting right...

Background -
The engine ran very hot yesterday (261) as for some reasons the cooling fans were not coming on and I did not notice, though it was only a short journey. I got home, due to hearing the "parping noise" and then tried to listen to the engine when still, but the noise isn't discernable at a stop. It was while doing this check that I noticed the engine was hot, but I can't be sure if it had been hot earlier or just at that time.

The cooling fans seemed to come on no problem today, I did some wiggling of the relays to test them (shorting the A-B pins on the ALDL) and maybe that fixed a loose connection. Don't know, but they're on now and engine was fine heat-wise.

Other than running hot, there is a slight vacuum leak hiss (has been for a while, was not apparently affecting anything) from under the plenum.

That's all I can describe. I'm going to comb through the forums to understand more, but any quick hints as to what I could / should check? Could I have blown a head gasket (would it give these symptoms) due to the heat? Will check oil for chocolate milk froth, and coolant for oil shortly...

Any help appreciated. Will write back to the thread as and when it's resolved (these forums are great when you read a problem and the OP posts the resolution :-) )

Thanks all.

Steve

- Edited to add:
Car is stock.
No service engine light on.

[Dynomite]

What is "Parping" exactly?
I think 260 is almost in the red.....but.........if you had coolant flowing vice blowing out coolant reservoir....and if only for short time.....

Guess I would check compression on all eight cylinders and do the secondary check with plenum in place.

Keep an eye out for oil in coolant and coolant in oil or coolant leaks anywhere. If this "Parping" was a result and directly related to your over heating issues.....then something obviously changed during that heat cycle....somewhere.

Checking Function of Secondaries with Plenum In Place

A sound that parps, as of a horn or trumpet

There is another definition of that sound involving a P-38 pistol.....

Now if the engine no longer makes the "Parping" sound and only when it was very hot.....I think the "Parping" sound was coolant boiling over popping out the pressure relief of the radiator cap on top of the coolant reservoir in front of the passenger side. Or......cavitation of the water pump as steam pressure built up in the coolant system where you exceeded the boiling point of the coolant.

But......I see you say you hear "Parping" above 3500 rpm SINCE the overheating issue.

Or.......you have head gasket leak and excessive air pumping into the coolant and out the pressure relief of the radiator cap on the coolant reservoir. Check coolant overflow container during idling after the engine has reached operational temperature to see if there is a lot of bubbling into the coolant overflow container located under the passenger side headlight.

[GOLDCYLON]

I have no idea what "parping" is but is sounds like what im reading that you are having a serious miss. Any SES light? Do you have any codes that you have pulled? Did the check guages warning light come on in the IP?

You are going to have to pull the plenum regardless since you have been hearing a hiss for a long while and check you conntections. It like a vac secondary failure or a secondary system failure.

261 is rather high which is why I asked about the check guages. If the 261 registered on the digital guage using the guages function what did the analog temp say ?

[PhillipsLT5]

261, the head gasket?

[GOLDCYLON]

Originally Posted by PhillipsLT5

261, the head gasket?

Among other things... Yep a possibility

[c4koh]

Guys - thanks for the comments.

To the questions:

• No SES lights on permanent nor came on temporarily.
• When I saw the 261 overheat (2 days ago), both the analog gage was reading about 260 (it looked around 259, just under 260) and the digital gage read the same temperature. In any case, for whatever reason, non of the cooling fans would come on, but this is now seemingly resolved.
• There is no frothing at all in the oil - it's clean, no bubbles, looks like fresh oil. There's no bubbling over to the coolant overflow reservoir when up to temperature, and no oily film.
• There is no white smoke at any time from the exhausts.

I drove it more today, and first the "parp" (hey, I'm British living now in the US, you know we're separated by a common language ) was actually more the effect being rebounded in the cabin due to the roof off.

So, more explanation:
Drove it more, and after coolant got up to 180 or so, with the secondaries (power key) ON, the car drove perfectly - fast, screamy, revving and breathing like it should. Marked effect between full power and normal power, as I'm used to.
About 10 minutes into the drive, the problem re-occured, and it does sound more like mis-firing. Sort of like the sound you get driving over the rumble strip, and only audible over 3500rpm, but certainly reduced power (but still quick).

The frequency of this rumble sounds around 900 rpm at 3500 rpm, which being 1/4 of the RPM would indicate a miss of some sorts. I cannot hear any miss when stationary and revving to 3-4000rpm, it seems to only happen (or be audible) when on the road / under some load.

Summary -

No visible evidence of coolant/oil mixing based on the easy-to-inspect things.
Car drives well for first 10 minutes, and certainly well on full power during that time.
After 10 mins or so, begins to sound mis-firing / rumbly.

I'm letting the engine cool down now and will look at the spark plugs next for any clues.

Any other hints?

[GOLDCYLON]

Original injectors?

Where are you from? I was born in the Midlands Northanpton to be exact ?

[c4koh]

I'm from Liverpool, and had a 92 LT1 then a 91 ZR1 while in England, moved over to the US in 2009 and was vette-less until April this year when I got a 92 ZR1. Northampton - nice place, and well-known for its great (but expensive!) shoes.

For the injectors, yes original. But not sure why the car runs fine for first 10 minutes or so, would have thought an injectors issue would show up immediately?

It seems that once the car is fully warmed up something happens. Since I read that the stock thermostat opens around 195-203 degrees, and the engine takes around 10 minutes or so to get to this temperature, then it woudl seem to coincide with the condition occurring.... And if I read further, the secondaries are active with the power key on much lower (oil and coolant need to be above 68F)... so this may explain the good running for a short while, and a clue as to why the problem seems to occur about 10 minutes in to the drive... ?

[PhillipsLT5]

Originally Posted by GOLDCYLON

Original injectors?

Where are you from? I was born in the Midlands Northanpton to be exact ?

Injectors?

http://zr1specialist.com/HAT%20Web/a...eplacement.pdf

http://zr1specialist.com/HAT%20Web/a...in%20Place.pdf

http://zr1specialist.com/HAT%20Web/a.../injectors.htm

Do not get factory or rebuilt

[GOLDCYLON]

Im thinking it might be the secondary injectors. Good time to replace all 16 while you are thers since you need to do a plenum pull already