I purchased a 94 Z28 about three weeks ago (95k miles, all stock except for exhaust and K&N CAI). It ran fine on test drives but once I got it home I noticed it was quickly getting hot (near redline) when driving in town. I replaced the thermostat (my first ever effort towards mechanical self-sufficiency) then I took it to a mechanic who replaced the water pump and radiator. A couple days after getting it home I noticed a new leak from the front of the engine (the mechanic also left the elbow partially connected to the throttle body and did not reattach the a.i.r. hose - needless to say I won't be taking any automobiles back to him - however the car was running well after I reconnected these items). Today the car cranked for about five seconds before starting, then barely ran after it started (I could press on the gas but there was very little response). I parked it in the garage and it will now start sometimes, but still requires quite a few cranks before turning over. Other times it will crank and crank without starting - it does sound like it's going to start, but does not. When it does start, it surges to 1200-1500 RPM immediately upon starting, then settles into a rough feeling idle.

In an effort to take ownership of this car and learn more about how all of this works, I'd like to try to work on this car myself. So far I've tried the following:

1. In-line spark tester: results showed a spark at the most easily accessible plug. The spark flashed and according to the packaging this indicates a fuel system problem, but I'm not sure if this is always true.
2. Fuel pressure test: results showed 0 pressure with the key in the on position. There is a noticeable "whine" (not sure if this is the right descriptor, but it sounds like an electrical whine) when the key is turned to the on position. After starting the car, the pressure builds but seems to stop at 10-15 psi about a minute or two into idling.

My fear is that the mechanic installed the water pump poorly causing the new oil leak, and that the oil has leaked onto the optispark. However, if the fuel pressure tester is accurate, the fuel pressure symptoms seem like they might suggest fuel pump/fuel filter/fuel pressure regulator. Does anyone have any thoughts on where to go next? I've read plenty of threads on similar issues but none expressed exactly these same symptoms. As I mentioned, I'm new to independent car care so any advice is appreciated. Thanks all!

NG

 

High idle and excessively rich start can be the result of a problem with the coolant temperature (CLT) sensor mounted at the bottom of the water pump housing. See if it was damaged.

From Shoebox:

http://shbox.com/1/temp_sensor1.jpg

Are you sure you got the correct thermostat for the LT1?

http://shbox.com/1/tstat.jpg

What temperature?

If the mechanic didn’t install the water pump driveshaft seal correctly in the timing cover, you will have an oil leak behind the water pump, dripping on the Opti.

Did your fuel pressure test gauge have the pin required to depress the pin in the Schrader valve so it could get a pressure reading? Check the pressure as the fuel pump primes and shuts off. It only runs for 2 seconds after you turn the key to run. When the pump shuts off, watch how fast the pressure bleeds off. Rapid loss of pressure can result in extended cranking times at startup.

 

Injuneer,

Thank you very much for the reply and especially for the pictures! Seeing all of these things for the first time, it's easy to get lost if I don't know what I'm looking for.

The CLT sensor came apart when I tried to unclip it - that is, the black plastic plastic housing that comes out of the metal bung (not sure if this is the right word here) crumbled, so it will certainly need replaced. I'm headed out to get a new one now. Any tips on replacing this? I only ask as it looks like the current sensor is surrounded by white sealant of some kind. I've watched a couple of videos online and none of them mention adding any sealant, so I was surprised to see it there.

Regarding the thermostat, I believe I purchased the correct item ( https://www.oreillyauto.com/detail/b...rmostat&pos=10 ). Prior to todays problems, it had been running fine with the thermostat I installed.

I removed the elbow from the fuel pressure test kit and I now get 5 psi when I turn the key to the on position, it immediately bleeds down to 0 once the fuel pump stops running. When the engine does start, I get 15 - 20 psi.

Thanks again and please let me know if you think I need to be adding sealant to the CLT install. I appreciate your feedback, I'm off to get a new sensor.

Cheers!

NG

 

@Injuneer Ive installed the new sensor - no sealant required. She is still cranking without starting sometimes, and running poorly when she does start (very little acceleration, almost no throttle response, rough idling, essentially undriveable). While replacing the sensor I did notice a great deal of oil behind the water pump. I also noticed a strange smell on startup but I can’t place the smell.

Additionally, I noticed that the fans kick on immediately on startup and the SES light is also now on. I’m not sure if these new clues make things more clear or even muddier. Regardless, thank you for the reply and any future insight you might feel like providing!

NG

 

Did you check the CLT sensor’s 5 volt reference voltage per the Shoebox procedure? Maybe there's a pinched wire causing a short.

Is the SES light on? Do you have access to a scanner to check for codes? A badly damaged CLT sensor should have set a code. A code could turn on the fans continuously.

Not unusual to use some white Teflon sealant/tape on the sensor threads. If it was a 1-wire sensor, relying on the threads for a ground, it could be a problem to use sealant. But the 2-wire sensor is grounded through the reference voltage.

Fuel pressure should prime to at least 40 PSI before the pump shuts shuts off. Rapid loss of fuel pressure when the pump shuts down could be:

- leaking injector(s)

- leaking fuel pressure regulator

- leaking line including the pump flex line in the tank

- leaking fuel pump check valve

Spec for engine operating fuel pressure is 43.5 PSI, measured with the vacuum compensation line off the pressure regulator. GM spec tolerance 41-47 PSI. Might want to check with another pressure test gauge just to be sure.

Free download of 1994 factory service manual courtesy of GaryDoug:

https://www.mediafire.com/?40mfgeoe4ctti

 

The whine you hear at start up is the fuel pump.. which means it's working (how good i don't know)..
The fans will kick in when SES Light turns on.. it is kind of a safety messure to protect the engine..

start with replacing the cheap stuff (yet very important to take care of) specially since you just bought the car..
Injuneer had a post a while back regarding maintenance requairment you will need to check and replace.. i couldn't find the post but have a snap picture of it on my phone..

replace PCV valve and Hoses (DIY)
replace Fuel filter (DIY)
replace Spark plugs and spark plugs wires (DIY)
replace Coil and Coil wire (DIY)
change Coolant (DIY)
change Engine oil (DIY)
change Transmission oil (DIY)
change Rear differential oil
change Break Fluid
change Steering fluid
replace Ignition control module (DIY)

doing this list will get you familiar with your car and where things located and get a (Race Ramp) if you decide to do the work.. they help a lot.. but you gotta stop the oil leak on top of the opt as quickly as possible.. if it is not the collaborate.. soon it will be..
good luck and congrats on your Z..

 

@Injuneer Thanks for the documentation - this is helpful. The SES light is on - I do not have a scanner at the moment, though I can obtain one. I've read some confusing perspectives about tuning/diagnosing 94 Z's (confusing to a newbie anyway) - is there a "best" tool to obtain for this purpose? I did run the reference test per Shoebox's instructions (what a great site) - and it looks like the lead/harness is getting the proper 5v.

@Corona95 Thanks a lot for the direction! I did change the oil and filter after I got it back from the mechanic. I used Mobile 1 5w30 and it was running well after the change. I drained the coolant and replaced it - it was immediately changed again with the radiator and water pump replacement. The other items are on my list (I've seen the post you speak of, it's the first time I'd seen Injuneer's name pop up) but have been interrupted by the major problem that popped up (I've read that changing plugs and wires could help with the problems I'm experiencing so they will be part of this run of changes).

To both of you and anyone else reading - thank you. To update - I've replaced the engine coolant sensor (yesterday), and I replaced the fuel filter today. The fuel filter drained some gross looking stuff that certainly was not all fuel, so while it wasn't the culprit, it absolutely needed replaced. After replacing the filter I tested the pressure again. The pressure still only goes to 5 psi when the pump kicks on, and immediately falls back to 0. I know the test kit works as my 97 silverado tested just fine and held it's pressure after the pump turned off. So maybe the Z has a bad schrader valve but given the other problems I'm experiencing, I would think it makes more sense to look to the fuel pump and/or fuel pressure regulator. I've read that a new regulator can improve throttle response so it was already on my list anyway.

Last piece of (seemingly) useful information: when it starts (maybe 50% of the time) throttle response feels a lot more accurate when I throttle slowly than when I step on it. I'm not sure if this means anything but I thought I'd share it in case it clicks for someone else.

Thanks @Injuneer and @Corona95 - if the new information triggers any thoughts, please send them my way! And thanks to anyone else reading who might have an idea. While frustrating to pay for something that now needs so much work, I'm learning and I'm enjoying the ride!

NG

 

The 94 PCM requires software to flash the tune. There's some background on what is available, and how to tune here:

LT1 PCM Tuning - Tips & Tricks for DIY Tuning!

The best diagnostic software is Scan9495, written specifically for the 1993-1995 LT1:

https://www.camaroz28.com/forums/com...95-lt1-874306/


The fuel system builds pressure based on the fuel pressure regulator closing off return flow to the tank. You can check for a leaking FPR by blocking the return hose. But that is difficult to do, without the factory tool for temporarily inserting a valve in the line. Do not try and pinch the nylon fuel return line, because that can damage the line to the point of causing a fuel leak. The FPR is either working or not working. There is no reason "a new regulator can improve throttle response" if it wasn't defective.

Can be a problem with the throttle position sensor (TPS), or there could be an air leak in the rubber elbow connecting the MAF sensor to the throttle body. The elbow can crack from old age, or the bottom of the elbow may not be fully over the bottom lip ot the throttle body.

 

@Injuneer Thanks again! I appreciate the details re: tuning and diagnostic software. It looks like ALDL cables are about $55 so I'll get ahold of one soon. I've got an old laptop so I should be able to start trying this out once I get the car back...

In the meantime - I decided to take the car to a mechanic (a different mechanic than the one who created the oil leak) and they confirmed my results on fuel pressure. They tested the fuel pump and confirmed that it needs to be replaced. They noted the oil around the opti but (fingers crossed) don't believe the opti has been fouled. I asked them to clean it and confirm functionality while they have the water pump off to fix the oil leak. I don't believe I have the skills/knowledge to replace a fuel pump and fix the leak at the water pump (without creating new problems for myself), so I'll be paying to have these two jobs done. I'm hopeful that this gets the Z running well again so that I can continue down the list that you and @Corona95 have mentioned.

Thanks again to both of you - wish the Z luck with the new mechanic!