car pulsates under load when in power mode
 

I just bought a 1991 corvette zr1 and i dont find any difference when i switch from normal to power mode. in normal mode the car drives fine. when i switch to power mode, the light comes on. car still feels like 210 hp and when i accelerate heavy, the car pulsates and vibrates. when i let off and drive normal, the pulsation goes away.

im thinking its the secondary injectors that may be the problem as i continue to read in the other posts.

I would like to be sure before i invest in them. Also, if it is the injectors, is there anybody you can recommend with a decent price? Im from Canada if that makes a difference. Maybe the local parts shop can order from a major supplier.

sorry, one last thing... any advice or tricks to do an oil change? and is it true the zr1 takes 12 litres?

thanks in advance!:dancing

Re: car pulsates under load when in power mode
 

Being a 1991, injectors are certainly a likely explanation. If they are original, I'd bet on one or more being faulty.

Many aftermarket brands available - Accel, RC Injectors, FIC (sells reconditioned Bosch units, popular because they're about half the price of the others).

Oil change tricks? Elevate car, remove drain plug, drain oil. Reinstall drain plug, change oil filter, refill with oil. Takes about 9 quarts for a typical oil change. There is oil that remains in the oil cooler plumbing, 3-4 quarts, which cannot be drained easily.

Re: car pulsates under load when in power mode
 

As stated bad injectors.

Re: car pulsates under load when in power mode
 

One more note on the oil change. Make sure about doing one or the other.

1. Draining hot: best to drain overnight if possible (My Personal Favorite), 3 or 4 hrs minimum.
2. Draining cold: Drain until slow drip, button up & fill to full on dipstick. If new filter, check again later when cold & top off.

The LT5 is slow to return oil from the top end to the pan. Doing a standard, quick hot drain & refill can easily result in overfill.

Re: car pulsates under load when in power mode
 

You will never get in that much as 3 quarts are left in the oil cooler. 8.5 or 9 is about what mine takes.

Re: car pulsates under load when in power mode
 

I'm acutually exeriencing a similar issue where I can't tell much of a difference between "Normal" and "Power" modes. If the issue lies in the secondary injectors, would that throw of a code, or a warning light? Is there a way to check if the secondary injectors are bad without pulling the plenum?

Re: car pulsates under load when in power mode
 

From Marc Haibec's website:

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

A word of caution, DO NOT force your volt meter probe leads into the female pins of the ECM plug.
Save yourself the agony that only took me 2 years to diagnose and repair on my ZR-1.
Shoving the probe leads into the pins serves to stretch out the female connector and then they won't make good contact with the male pins in the ECM.
Causes all kinds of mysterious intermittent problems.

Back-probe the pins instead, simply pull the rubber plugs out with needle nosed pliers.
When you look carefully at the ECM plug you will see what I mean.

Good luck!!!

TomC
'Crabs

Re: car pulsates under load when in power mode
 

Based on the symptoms you describe I would start by looking for a problem in the secondary throttles vacuum system.

I had a similar problem with my 1994 when I bought it.

The first easy check is when you turn the ignition key to ON without starting the car, do you hear the Secondary Vacuum Pump run for a few seconds and then turn off? The pump is located just forward of the coolant overflow bottle, near the pass side headlight.

If the pump doesn't run at all, it needs to be replaced before you can do any other analysis.

If the pump runs-stops-runs-stops-etc, then you have found that there is a vacuum leak that you will need to fix before you do any other analysis of the injectors.

Another quick way to test the vacuum pump is to find the thin plastic vacuum tubing that runs from the vacuum pump to the engine. Right near the alternator, there is a connection that you can separate. With the ignition key on, pull that vacuum line connection apart and by putting your thumb over the end of the tubing coming from the pump you can easily check its operation.

Post up and let us know if you vacuum pump is working.

Jim

Re: car pulsates under load when in power mode
 

Hi and welcome to our corner of the asylum!:hello:

I would ask do you know when the fuel filter was last changed out? They are out of the way & get overlooked. No SES light when you try to make it accelerate? Then the light goes out when you relent? Check CCM as it may store that soft DTC.

It sure sounds like it's starving for gas when you want the secondaries, but why?
2* injectors check Ohm readings hot. Ohm okay = good coils, but could be clogged tips.
2* injectors for fuel flow, could be injectors or fuel pumps. 55 PSI on rail is top of the range, FSM says 48 - 55 PSI. Check regulator hose for fuel, if fuel present regulator is N/G. Pump socks clogged?
2* vacuum system could have: a vacuum leak or bad actuators.
Collapsing air intake duct from filter housing to air horn.
These are some of the things you could look at. Not trying to make work for you. Are the injectors OEM, if so they maybe the most likely cause of the trouble.

:cheers:
Tom

Re: car pulsates under load when in power mode
 

On the oil change and the stated capacity of 12 qts.

After tearing down several LT5's, I come to the conclusion that there may be a qt of oil in the oil cooler. The rest is in all sorts of little nooks & crannies in the cylinder heads, lifters, oil filter housing. etc. , that just never drains down. The appx 12 qt capacity is for a new, completely dry engine & filter.

I've cleared my oil cooler before with an oil change and doesn't even come close to 11qts.