"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 (http://www.zr1.net/forum/showthread.php?p=207184)

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]

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 :p) 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 ? :cheers:

[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]

Original injectors?

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

http://zr1specialist.com/HAT%20Web/articles/Fuel%20Injector%20Replacement.pdf

http://zr1specialist.com/HAT%20Web/articles/Measuring%20Fuel%20Injector%20Resistance%20with%20 the%20Plenum%20in%20Place.pdf

http://zr1specialist.com/HAT%20Web/articles/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

[XfireZ51]

Ask Pete what happens when your motor heats up to 261.

[Dynomite]

Ask Pete what happens when your motor heats up to 261.

Well? Is this assuming coolant boiled off and water pump cavitated....then things went South quickly?

So.......how bad can it get? And how did Pete's situation happen?

I thought I had the rarest. New water pump. Fired it up and went for a drive....impeller spun free of input shaft on new water pump. I caught the temps before they got into red zone.

[c4koh]

The engine got to 260 for not more than 10 minutes, and I can't be sure it was that hot when driving it. Coolant was always fine (water never boiled off).

In any case....

Suspect #1 from the threads above re: injectors. I just went and tested the resistance across all of them, and...

(I read it should be 12.1ohm +/- 0.1ohm at 68F. Today was 90F (the engine probably a bit warmer too, as I tested about an hour after a short drive to get coolant to 210), and none checked out at 12.1ohm, the "good" average seemed to be 12.9ohm. My notes on this (I think they're from Marc Haibeck) notes that 13.5 around 30 minutes after warm is a good average, so I presume my 12.9 is about right given the time/temp.

For reference:
PRIMARY INJECTORS
#1 12.8 ohm
#2 13.0 ohm
#3 5.8 ohm
#4 12.9 ohm
#5 13.1 ohm
#6 13.0 ohm
#7 12.8 ohm
#8 12.9 ohm

SECONDARY INJECTORS:
#1 6.3 ohm
#2 0.7 ohm
#3 11.4 ohm
#4 3.4 ohm
#5 6.3 ohm
#6 12.8 ohm
#7 8.7 ohm
#8 5.9 ohm

As can be seen, Primary #3 looks bad, and pretty much all except #6 of the Secondaries look poor!

So certainly will replace these, and while under the plenum fix the vacuum leak. I hope that with no evidence (so far) of white smoke, oil in coolant, and coolant/froth in oil, that hopefully (fingers tightly crossed) that the rumbling is just a mis-fire from the injectors not fully functioning...

This being said, for my own interest and knowledge (will try and look up the answer in the meantime):

A "bad" injector (concluding it's bad from the off-par resistance) still functions, just badly, right? And perhaps in my Secondary #2 (resistance at 0.7 ohms) it's just shot?
When they're "shot" - do they let in any fuel (as basically drips rather than nice injected spray) or do they simply clog up and not allow anything.

Still unsure why the car drives fine and powerfully until it's at least warm, and seemingly with no problems (and very, very fast) with POWER KEY on.

Thanks all so far for the help. Will report back once I've replaced the injectors.

[We Gone]

I thought I had the rarest. New water pump. Fired it up and went for a drive....impeller spun free of input shaft on new water pump. I caught the temps before they got into red zone.

I've had 2 in unopened box NOS pumps do this....only pulleys spun off shaft.

[tccrab]

A "bad" injector (concluding it's bad from the off-par resistance) still functions, just badly, right? And perhaps in my Secondary #2 (resistance at 0.7 ohms) it's just shot?
When they're "shot" - do they let in any fuel (as basically drips rather than nice injected spray) or do they simply clog up and not allow anything.

Still unsure why the car drives fine and powerfully until it's at least warm, and seemingly with no problems (and very, very fast) with POWER KEY on.

Thanks all so far for the help. Will report back once I've replaced the injectors.

The coil in the injector opens and closes the pintel which controls the flow of the spray. If the pintle doesn't open all the way the spray pattern gets erratic (think of your sprinklers in your front yard).
A bad injector can spray badly or drip fuel or in the worst case do not work at all.
As to why your motor runs worse when it's warm, that's quite simple. Resistance and temperature share an inverse relationship.
As temperature goes up, resistance goes down and a marginal injector becomes a non-working injector.

As far as injectors, unless your budget demands otherwise, go with new injectors. I've had great luck with Accells, FIC sells new ones, and at the top of the price spectrum is RC Engineering, but by all accounts they are the best.

Of course, Jerry more than likely has everything you need in stock and I'll bet that if you send him an email today you will have the parts early next week.

Good luck!!!

'Crabs

[Franke]

Gold Cylon and Tccrab is right on. Replace the injectors ASAP. My car had 1 bad primary and 3 bad secondary injectors and it ran good cold but only until I got on it did I realize the lack of power in the secondaries. I had and you will have a slight miss at idle with the bad primary injector when the engine is hot but probably not when it is cold as the coils in the injectors regain some of their resistance cold. Saw it for my self with a hot then cold injector test. When the injectors short out (drop in resistance) they do not provide the fuel needed for the present engine condition. I had a friend with a 91 L98 that ran great for about 45 minutes and completely quit until it cooled down again then it would start and run fine for a short bit and repeat. He had 5 injectors that were bad. WE replaced all 8 of them and he said it was like a new car.

[PhillipsLT5]

Ask Pete what happens when your motor heats up to 261.

http://zr1specialist.com/HAT%20Web/products/mls%20head%20gasket.htm

[Kevin]

looks like what injectors were when I replaced them the first time. All of yours need to be redone, fuel injector connection is who you need to call

[c4koh]

The coil in the injector opens and closes the pintel which controls the flow of the spray. If the pintle doesn't open all the way the spray pattern gets erratic (think of your sprinklers in your front yard).
A bad injector can spray badly or drip fuel or in the worst case do not work at all.
As to why your motor runs worse when it's warm, that's quite simple. Resistance and temperature share an inverse relationship.
As temperature goes up, resistance goes down and a marginal injector becomes a non-working injector.


Great - I read up on them (fuel injectors) , and I see now how they work. The magnetic field induced moves the pintle by the electric current passed to the solenoid wiring/coils. So, presumably a fresh/good coil has a good winding, and reasonable resistance. As it gets gunked up, the coil works worse, likely touching each other providing parallel resistance paths (and hence reducing overall resistance) and so on.

Will read up about which injectors to get for my budget (noting already the ethanol-averse stock and rebuilt ones, so not going for those), and also what else to do while under the plenum. I've removed the plenum on my old ZR1 (when back in England) and re-used the gasket the first time, but put on the new gasket the second time. It's been 7 years since I last removed the plenum, but it was easy enough with the right instructions, patience, and digital camera to record everything I removed... to remind me what to put back... :)

Thanks again all for their help.

[Kevin]

Stay away from the rebuilta