engine knock and t-stat problem

[cmhass2]

Just pulled the plenum to repair a vacuum leak. It was repaired successfully and this brought down a high idle. Drove fine for a couple days. I noticed engine knock last night for the first time in the four years I have owned the car. I have also recently replaced the fuel pump assembly and fuel filter. In addition, I have noticed there is not much difference between the upper and lower radiator hose temperatures (thinking t-stat may need replacing-directions on how to do so would be much appreciated). Any ideas as to what may have caused this or how to fix it. Was it a transient one time thing? Was it related to my other issues? Thanks for any input in advance!!

[tccrab]

Originally Posted by cmhass2

Just pulled the plenum to repair a vacuum leak. It was repaired successfully and this brought down a high idle. Drove fine for a couple days. I noticed engine knock last night for the first time in the four years I have owned the car. I have also recently replaced the fuel pump assembly and fuel filter. In addition, I have noticed there is not much difference between the upper and lower radiator hose temperatures (thinking t-stat may need replacing-directions on how to do so would be much appreciated). Any ideas as to what may have caused this or how to fix it. Was it a transient one time thing? Was it related to my other issues? Thanks for any input in advance!!

Highly unlikely that you've spun a bearing or dropped a rod unless there's something that you're not telling us.
Dual Mass Flywheel rattle from a misfire can sound pretty scary.
Tell us more about your car.
What year?
Mods?
Mileage?
Have you ever replaced the injectors?
Do you use the right coolant?

Interesting observation about temperature differences between upper and lower radiator hoses, must have been pretty darn difficult to reach the lower one.
What does the gauge tell you?
Thermostats aren't usual failure items, however a few who live in warmer climates have changed them out for extra cooling.
And people with modified motors gain some extra cooling by putting in lower temp thermostats.
Most with cooling issues find that their radiator responds well to cleaning out all the debris that our "bottom sucker" cars collect.

Bottom line is, need to know a lot more before we can make any really accurate arm chair diagnosis on your car.

TomC
"Crabs

[cmhass2]

thanks for the response. Here is some extra info.
1991 ZR1 80k miles, aftermarket exhaust, i have not replaced the injectors, i also use platinum plugs and aftermarket wires, florida car (just moved it from ohio 2 weeks ago), I'm not sure if the coolant is the specfic type for the zr1 (had a heater core replaced and not sure what they put back in), I used one of those infrared thermometers and put it on both lines and both showed about 190's, but there are many times I drive in traffic (especially now in FL) where the gauge get very close to the 260 mark( i have heard c4 vettes are notorius for dash cluster problems that cause the reading to be off). However, infrared thermometer never gets over like 220-230. I had the coolant temp sensor checked when I plled the plenum and was told it was ok.

[tccrab]

Originally Posted by cmhass2

thanks for the response. Here is some extra info.
1991 ZR1 80k miles, aftermarket exhaust, i have not replaced the injectors, i also use platinum plugs and aftermarket wires, florida car (just moved it from ohio 2 weeks ago), I'm not sure if the coolant is the specfic type for the zr1 (had a heater core replaced and not sure what they put back in), I used one of those infrared thermometers and put it on both lines and both showed about 190's, but there are many times I drive in traffic (especially now in FL) where the gauge get very close to the 260 mark( i have heard c4 vettes are notorius for dash cluster problems that cause the reading to be off). However, infrared thermometer never gets over like 220-230. I had the coolant temp sensor checked when I plled the plenum and was told it was ok.

Better.
First things first.
Tell us about this knock.
When is it.
My bet is at idle.
Speaking of idle, how is your idle?
If your car is running right you should be able to balance a nickel on edge on the top of your plenum.
I kid you not.
If it's got a miss at idle, you are hearing your dual mass flywheel rattle.
First thing that comes to mind is fuel injectors.
It's probably time to replace 'em.

I'm gonna guess that Florida is a little hotter than Ohio this time of year, and yes, your car will run hotter, especially in traffic.
You might want to consider buying a prom that turns on the cooling fans at lower temps to help moderate underhood temperature.
But I'd recommend that you clean out the radiator first.
It's quite a chore, but you might not have to break open your cooling system if your radiator is full of bugs and dirt.

Coolant, ONLY use the green stuff. Otherwise you risk losing head gaskets.
Do a search on coolant, there's quite a few posts about it.
If your coolant is anything other than good old green dexcool you could be in an expensive world of hurt.

TomC
'Crabs

[cmhass2]

The story continues,
Idle was rough this morning. The knock is much more noticeable for sure at idle. I haven't done the injectors yet. Power also seemed to be lacking. However, its seemed to smooth out about 20min into driving this morning????? Bad gas? I hope it continues running well The good news is the coolant is green (thank god based on the stories i've heard). Based on having a computer plugged up to it recently I was told idle was 800rpm.

[tccrab]

Originally Posted by cmhass2

The story continues,
Idle was rough this morning. The knock is much more noticeable for sure at idle. I haven't done the injectors yet. Power also seemed to be lacking. However, its seemed to smooth out about 20min into driving this morning????? Bad gas? I hope it continues running well The good news is the coolant is green (thank god based on the stories i've heard). Based on having a computer plugged up to it recently I was told idle was 800rpm.

I'll lay odds that you've got injector problems and the knock is the Dual Mass Flywheel.
The original Multecs aren't compatible with today's gasoline.
This is a *very* common problem with '90-92 ZR1s.
http://www.zr1netregistry.com/ZR1_issues.htm#34
There are a few options for new fuel injectors, from highest price to lowest, OEM Multec (will fail again, they never updated the design), RC Engineering, Accel, FIC.

Green coolant is good.


As far as the heating issue, cleaning the radiator is by far your cheapest option.
I'd also seriously consider buying a prom from one of the tuners that turns the fans on at lower temperatures. I've got a Haibec chip and I've never had a cooling problem, even in 100+ California heat.
Of course I must add in all honesty that my Z isn't a daily driver and I've never put it to the test of bumper to bumper traffic in the heat of the day with the AC on high.
I'd have a chat with "Goldie" (GoldCylon), he drives his Z daily in Phoenix and he did a bunch of cooling system mods to help keep it cool. I'm sure he's got lots of useful tips, ideas, do's and don't do's.
As far as changing the thermostat, there's info here on Dynomites' "Solutions" link page:
http://www.zr1.net/forum/showthread.php?t=11619
One word of warning, the thermostat is in a separate housing that's fairly fragile and it's made of "Un-obtanium".
Should you or your mechanic fubar it trying to change the thermostat you will be in for a shock.
A few have sold over the last couple of years and the price was a real eye opener to say the least.

TomC
'Crabs

[LGNDLT5]

Originally Posted by tccrab

Better.
.

Coolant, ONLY use the green stuff. Otherwise you risk losing head gaskets.
Do a search on coolant, there's quite a few posts about it.
If your coolant is anything other than good old green dexcool you could be in an expensive world of hurt.

TomC
'Crabs

HI Tom. Just an observation. DEXCOOL is NOT green. Traditional Ethylene Glycol was and still is green. The COLOR should NOT be relied on as a determination for proper coolant. The coolant manufacturers have changed colors to fool consumers and support their claims of compatability with "all" coolants. (I believe but am not sure I remember accurately) that the potential for damage to head gaskets etc. is when the 2 types are mixed as they have vastly different chemical compositions and are not compatible for mixing. Our cars came with both types depending on Year. Please do your research or you may regret the results. Sorry to jump in but the archives have all the details. John

[tomtom72]

Hi, pardon me, but I'd like to just add my two cents on some of the things that Tom and John have said.

The knock at idle could very well be a miss fire as the D/Mass flywheel will transmit that issue very well. The miss could be from a few sources, the common suspects are the OE injectors due to the alcohol in the fuel. However the wires and coils could also give you a miss. One thing with our wires is they are subject to lots of abrasion due to the tight packaging, so use a good grade of replacement wires. The stock GM replacements are very good just watch the aftermarket ones with thin insulation as cross sparking is a risk due to the tight routing.

The coolant, you have to be sure what was used, 1825-M spec GM coolant. Like John said do not mix a sillicated ( 1825-M ) with an OAT ( organic acid type aka DexCool ) or bad things can happen. I never trust anyone to do the coolant service in my 90. I do it myself so I'm sure which coolant type I'm using. Every two yrs on the service also.

Also, on our radiators....do the cleaning if you never had it out for that and if you never did the radiator air intake screen project. See this link at our home site: http://zr1netregistry.com/ZR1_radiatorscreen.htm

Trust me it's worth all the hassle to pull it and clean the trash that collects, and then do the screen. Also, at 80k it may be just worth while to buy a new radiator because besides the trash that blocks the air, the sand that gets stuck in the fins also degrades the cooling capacity. I did mine at about 15k and it took me hours & hours to pick the sand out! Also, the modified PROM idea is a great way to get the fans to do more work to cool the motor. I just bought one from Marc Haibeck and I still don't know why I waited so long. I guess I didn't believe it would make this much of a difference.

Oh, sorry, just another thought on the miss and then smoothing out after running awhile. That's not the usual symptom of OE injector coils going bad. The coils are what the alcohol attacks and they short out and the injector doesn't spray. Your injectors could be leaking a bit, flooded and a miss till it clears. Usually the OE ones aren't known for that, but age & miles could have something to do with the symptom you see. I'm just not positive. I would start it up and get out and take a sniff at the tail pipes to see what she's putting out....you know lean or rich smell along with any color to the exhaust gas stream...just a suggestion.


Tom

[Locobob]

In addition to the above suggestions you should check you coolant level and make sure the system is purged of air. Steam pockets can lead to localized hot spots and induce knock/spark retard.

[Hammer]

I would recommend just replacing the radiator if you are pulling it out.
http://www.corvetterecycling.com/199...p/52473260.htm

If you are going to do the injectors, buy from Jon at FIC. I have had his injectors now for over two years and the work great. Others have them also.

http://www.fuelinjectorconnection.co...ewCat&catId=68

Good Luck, keep us posted.