car pulsates under load when in power mode [Archive]

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zr1man@yahoo.ca

04-13-2011, 03:15 PM

VetteMed

04-13-2011, 03:28 PM

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.

GOLDCYLON

04-13-2011, 03:57 PM

As stated bad injectors.

A26B

04-13-2011, 04:49 PM

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.

A1990

04-13-2011, 05:39 PM

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.

| 1990 ZR-1 |

04-13-2011, 05:53 PM

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?

tccrab

04-13-2011, 07:27 PM

From Marc Haibec's website:

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

QB93Z

04-14-2011, 08:51 AM

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

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

tomtom72

04-14-2011, 09:11 AM

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

A26B

04-14-2011, 11:13 AM

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.

zr1man@yahoo.ca

04-14-2011, 11:43 AM

awesome thanks for the quick response!

Kevin

04-14-2011, 12:17 PM

awesome thanks for the quick response!

thats what we do here

Mahogaraunch

04-15-2011, 11:50 AM

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

I have the exact problem with mine! I have a 1990 ZR1 with 11,000km on it which was recently brought up from Florida. Needless to say, I got it out on the road after a long Ontario winter to find under the normal load the car drives perfectly. Under full power, the car shudders and there is no performance difference.

I have it going in this Monday for service, but I am not confident my garage has worked on a ZR1 before. What does anyone think the repair price for the injectors may run me? Does anyone have reservations about bringing a ZR1 to any garage? I am near the Peterborough area and am unaware of Corvette service shops in the area.

Thanks for the input.

zr1man@yahoo.ca

04-20-2011, 10:30 PM

I JUST ORDERED THE ACCEL COILS - ACC-140017 $41.00 EACH @jEGS AND ACC-150821 SECONDARY INJECTORS FROM SUMMIT RACING FOR $293 FOR SET OF 8.

GOING TO PULL THE PLENUM FOR SECOND TIME WHEN PARTS ARRIVE AND CHANGE THE WIRES WHILE IM AT IT. HOPEFULLY THAT WILL UNLEASH THE OTHER 200HP THAT I HAVE YET TO EXPERIENCE SINCE I PURCHASED THE CAR LAST YEAR.

YOU GUYS ARE GREAT AND ITS NICE TO ASK TECHNICAL QUESTIONS TO PEOPLE WHO UNDERSTAND THE CAR AND KNOW WHAT THEY ARE TALKING ABOUT...AS OPPOSED TO A LOCAL GM DEALER WHO DOESNT KNOW THE DIFFERENCE FROM A LT1 AND A LT5...I DIDNT FEEL TOO COMFORTABLE LEAVING THEM THE CAR TO TRY AND FIGURE OUT AT $85/HR.

sammy

04-21-2011, 10:06 PM

1990 415

04-21-2011, 11:15 PM

I have the exact problem with mine! I have a 1990 ZR1 with 11,000km on it which was recently brought up from Florida. Needless to say, I got it out on the road after a long Ontario winter to find under the normal load the car drives perfectly. Under full power, the car shudders and there is no performance difference.

I have it going in this Monday for service, but I am not confident my garage has worked on a ZR1 before. What does anyone think the repair price for the injectors may run me? Does anyone have reservations about bringing a ZR1 to any garage? I am near the Peterborough area and am unaware of Corvette service shops in the area.

Thanks for the input.

Have you asked this garage if they have ever worked on an LT5? Very unlikely they have. They will very likely make you wish you never took it to them. Only let an LT5 knowledgible person work on your ZR-1. Injector replacement isn't difficult to do yourself. Getting that first plenum pull under your belt is the key to really feeling like you are a brother of the beast. Don't let the inexperienced go near your LT5.

Kevin

04-21-2011, 11:29 PM

you'd be better off buying some beer and seeing who in the registry or list serve is nearby to lend a hand. if you're not on the list serve you need to be

Pete

04-22-2011, 04:45 AM

you'd be better off buying some beer and seeing who in the registry or list serve is nearby to lend a hand. if you're not on the list serve you need to be

How is the good old list serve?
Last time i was on there all they talked about was politics and advertising for Red Line nothing to do with ZR-1's or LT5's.

You wanna have some fun on the list serve mention Mobil 1 is the best oil and then sit back and enjoy. LOL

Pete

Paul Workman

04-22-2011, 06:02 AM

I JUST ORDERED THE ACCEL COILS - ACC-140017 $41.00 EACH @jEGS AND ACC-150821 SECONDARY INJECTORS FROM SUMMIT RACING FOR $293 FOR SET OF 8.

Until 93 MY the injectors were susceptible to alcohol. I would recommend purchasing 8 MORE of those same Accel (150821) injectors and replace them ALL now - prolly save you some grief again down the road. Once you have those injectors in, you B good. (You do know about the tabs being off-set on (I believe) the secondary injector, right? You'll have to grind or file off that plastic key on 8 of the Accel injectors before the connector will snap in place - took me about 10 minutes with a Dremel to do all 8.)

While you have the plenum off, one other thing you might consider is cleaning up the (solenoid) contact ring and perhaps the contact posts on the starter. They tend to get pitted and one day you'll have the dreaded "LT5 no-startums"...and another plenum pull. I bought a kit off of Ebay, but discovered the actuator shaft on the replacement was about 5mm SHORTER:confused: than the one being replaced. So, I used the new contact posts, but reused the actuator.

With an emery board I was able to easily remove the pitting on the surface of the contact ring and thus restore and retain the actuator "good as new". Start to finish it took about an hour - easily done.

Far as the secondary throttles go, if there is one item that pops up on this board consistently - especially among new Z owners - it is fixing the 16-21 year old vacuum circuit. Although parts to restore the system are available, many (most?) of the FBI gang and others too have pulled the secondary throttle plates, actuators, the whole shee-bang and are much happier for it! It requires the chip to be modified to run on all 16 injectors full time, but drivability, IMO, is enhanced. Once the injectors are changed, the secondaries eliminated, and the starter serviced, and the coils replaced...That is about IT for overhauling the stuff that rings up maybe 90% of the problems that pop up (on the board)! The argument for keeping the secondaries seems to center around passing emissions tests; having the secondary throttle plates in place increases the swirling effect in the chamber. Theoretically, this may help emissions testing, but I have not seen anything written here to suggest passing emissions tests is not possible or even inhibited by their (secondary throttle plates) removal. Just a thought.

YOU GUYS ARE GREAT AND ITS NICE TO ASK TECHNICAL QUESTIONS TO PEOPLE WHO UNDERSTAND THE CAR AND KNOW WHAT THEY ARE TALKING ABOUT...AS OPPOSED TO A LOCAL GM DEALER WHO DOESNT KNOW THE DIFFERENCE FROM A LT1 AND A LT5...I DIDNT FEEL TOO COMFORTABLE LEAVING THEM THE CAR TO TRY AND FIGURE OUT AT $85/HR.

Amen!

Welcome to the Brotherhood!

P.

jrd1990zr1

04-22-2011, 10:39 PM

I have the exact problem with mine! I have a 1990 ZR1 with 11,000km on it which was recently brought up from Florida. Needless to say, I got it out on the road after a long Ontario winter to find under the normal load the car drives perfectly. Under full power, the car shudders and there is no performance difference.

I have it going in this Monday for service, but I am not confident my garage has worked on a ZR1 before. What does anyone think the repair price for the injectors may run me? Does anyone have reservations about bringing a ZR1 to any garage? I am near the Peterborough area and am unaware of Corvette service shops in the area.

Thanks for the input.

Sounds like the same problem I had with my 1990 until I installed a set of new injectors.

FWIW, I wouldn't trust any non-GM dealer with a 1990 ZR1 (except the few specialists discussed by registry members). Likewise, there are very few GM dealers I would trust.

I recommend you check the injectors when the engine is hot to verify low resistance. Do the work yourself, there are a number of resources in the technical section.

Good luck :cheers:

zr1man@yahoo.ca

04-24-2011, 10:26 AM

I have the exact problem with mine! I have a 1990 ZR1 with 11,000km on it which was recently brought up from Florida. Needless to say, I got it out on the road after a long Ontario winter to find under the normal load the car drives perfectly. Under full power, the car shudders and there is no performance difference.

I have it going in this Monday for service, but I am not confident my garage has worked on a ZR1 before. What does anyone think the repair price for the injectors may run me? Does anyone have reservations about bringing a ZR1 to any garage? I am near the Peterborough area and am unaware of Corvette service shops in the area.

Thanks for the input.

Ive got a guy here in Bancroft (1hr away from Peterborough) that I trust to work on my ZR1 and going to use to help me re and re the plenum and install the injectors and coils. He is a perfectionist but not familiar with the lt-5. I think between this website for guidance and trouble shooting, and a skilled perfectionist like himself that I can use to help me do the install, we should be fine. Ill let you know how we make out with mine and if you want I can give you his number....he could come to Peterborough and give you a hand in your garage.

Also, in my travels i noted a Corvette specialty garage on the 401 somewhere between Oakville and cambridge...not sure where exactly but it was called Grand Sport Corvettes. Might be worth giving them a call and asking if they do service on lt5's.

batchman

04-25-2011, 03:48 AM

Just to chime in and suggest starting with something easy. I didn't believe it could be this simple, but someone here insisted and they were absolutely right.

Tighten the battery connections.

Worth a shot. You will need the other stuff anyway, but it seems the 2ndary fuel pump and injectors are a significant electrical hit and these side terminal batteries are marginal at best.

Best of luck,
- Jeff

Mahogaraunch

05-03-2011, 04:15 AM

Ive got a guy here in Bancroft (1hr away from Peterborough) that I trust to work on my ZR1 and going to use to help me re and re the plenum and install the injectors and coils. He is a perfectionist but not familiar with the lt-5. I think between this website for guidance and trouble shooting, and a skilled perfectionist like himself that I can use to help me do the install, we should be fine. Ill let you know how we make out with mine and if you want I can give you his number....he could come to Peterborough and give you a hand in your garage.

Also, in my travels i noted a Corvette specialty garage on the 401 somewhere between Oakville and cambridge...not sure where exactly but it was called Grand Sport Corvettes. Might be worth giving them a call and asking if they do service on lt5's.

I noticed when you quoted the part # from Summit for the secondaries, that the part appeared to be primaries only. I called Summit and the only secondaries they stated they had were for $180 per injector. Not sure if this part you quoted would work as secondaries?

Sorry guys, im not a handy tech guy like you all seem, and doing this job myself is out of my league by a long stretch. The references to Ohm's do confuse me. I have a good rapport with my garage in town but they have not worked on an LT5 before. I'm really not sure where to turn next as I brought the car to the garage and had the fuel filter replaced, the throttle body cleaned, and some injector cleaner placed in the tank. They thought if I drove it for a bit it would correct the problem. I took it out for a drive but as the weather has been crap have not had an opportunity to really drive it. I can hear the vaccuum pump running for several seconds when I turn the key to the accessory position, so that would not appear to be the problem.

Not sure if I want to invest $1400 for a set of 8 secondaries plus however long it takes the garage to install it without knowing for sure thats my problem with the car. With everything I read on this board I am confident the secondaries are my problem, but just not 100% sure.

Thanks for any input you guys have.

jrd1990zr1

05-03-2011, 10:45 AM

I noticed when you quoted the part # from Summit for the secondaries, that the part appeared to be primaries only. I called Summit and the only secondaries they stated they had were for $180 per injector. Not sure if this part you quoted would work as secondaries?

Sorry guys, im not a handy tech guy like you all seem, and doing this job myself is out of my league by a long stretch. The references to Ohm's do confuse me. I have a good rapport with my garage in town but they have not worked on an LT5 before. I'm really not sure where to turn next as I brought the car to the garage and had the fuel filter replaced, the throttle body cleaned, and some injector cleaner placed in the tank. They thought if I drove it for a bit it would correct the problem. I took it out for a drive but as the weather has been crap have not had an opportunity to really drive it. I can hear the vaccuum pump running for several seconds when I turn the key to the accessory position, so that would not appear to be the problem.

Not sure if I want to invest $1400 for a set of 8 secondaries plus however long it takes the garage to install it without knowing for sure thats my problem with the car. With everything I read on this board I am confident the secondaries are my problem, but just not 100% sure.

Thanks for any input you guys have.

I had similar problems with both my 1990s. Was bad secondary injectors caused by the E10 in gas.

FWIW, I bought a set of 16 injectors from Jon Banner (Fuel Injector Connection) for under $400. http://fuelinjectorconnection.com/shop/

http://www.corvetteinjectors.com/shop/viewcategory.php?groupid=3

Replaced them myself. I am definately not a tech guy. This was the first time I ever tried to do a repair such as this. If you use the instructions here on the registry and have a new set of primary o-rings and a spare set of plenum gaskets from Jerry's gaskets the job isn't that difficult. http://jerrysgaskets.com/store2/root/

Just make sure to drain the coolant down enough and use the procedure to refill coolant. This is probabily the most difficult part. :cheers:

A26B

05-03-2011, 11:58 AM

Awhile back, I started making up gasket & seal kits for the most commonly done procedures, in response to many emails asking "What all do I need?". Here's a link for the Fuel Injector Maintenance Kits, 90~92. The only choice you need to make, pertains to which type of seals you want.

Basically, Buna-N is best for 100% gasoline and also happens to be the least expensive. Viton is the best for Ethanol/Gasoline blends, but is more expensive.

90~92 Buna-N kit
http://jerrysgaskets.com/store2/root/index.php?main_page=product_info&cPath=16_19_20&products_id=458

90~92 Viton kit
http://jerrysgaskets.com/store2/root/index.php?main_page=product_info&cPath=16_19_20&products_id=459

Please note that virtually all new injectors come with o-rings installed already. That particular o-ring seal is PN1712222. If you are using new injectors, save some $'s, refer to the kit contents list on the website & get everything separately, except the 17112222 o-ring seals.

zr1man@yahoo.ca

05-03-2011, 12:35 PM

I noticed when you quoted the part # from Summit for the secondaries, that the part appeared to be primaries only. I called Summit and the only secondaries they stated they had were for $180 per injector. Not sure if this part you quoted would work as secondaries?

Sorry guys, im not a handy tech guy like you all seem, and doing this job myself is out of my league by a long stretch. The references to Ohm's do confuse me. I have a good rapport with my garage in town but they have not worked on an LT5 before. I'm really not sure where to turn next as I brought the car to the garage and had the fuel filter replaced, the throttle body cleaned, and some injector cleaner placed in the tank. They thought if I drove it for a bit it would correct the problem. I took it out for a drive but as the weather has been crap have not had an opportunity to really drive it. I can hear the vaccuum pump running for several seconds when I turn the key to the accessory position, so that would not appear to be the problem.

Not sure if I want to invest $1400 for a set of 8 secondaries plus however long it takes the garage to install it without knowing for sure thats my problem with the car. With everything I read on this board I am confident the secondaries are my problem, but just not 100% sure.

Thanks for any input you guys have.

now you have me wondering if i bought the right injectors from summit racing? i got the part number from this reference by a zr1 specialist.
http://www.zr1specialist.com/HAT%20Web/articles/Fuel%20Injector%20Replacement.pdf

he states that accel 150821 is a dirrect fit for the 91 zr1 and he uses this brand often on customers vehicles.

Can anybody confirm if purchased the right injectors for my secondary injectors? acc-150821 8-pack 21 lb/hr $300 from summit.

lbszr

05-03-2011, 12:41 PM

lbszr

05-03-2011, 12:48 PM

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

he states that accel 150821 is a dirrect fit for the 91 zr1 and he uses this brand often on customers vehicles.

Can anybody confirm if purchased the right injectors for my secondary injectors? acc-150821 8-pack 21 lb/hr $300 from summit.

That website is as good as the factory maintance manual. Looks like the same as 150121, only packaged with 8 and saves a little money.

Mahogaraunch

05-03-2011, 03:29 PM

Well, just ordered a set of 16 from Corvetteinjectors and the gasket set from jerry'sgaskets..

Anything else I need that anyone can think of? Spoke to my shop and they quoted about 3.5 hours to do the job.

Thanks.

zr1man@yahoo.ca

05-16-2011, 03:30 PM

just installed the parts i had mentioned before...secondary injectors and coil packs and it fixed the car! thanks guys for all the help and now i can enjoy the extra 200hp :)

tccrab

05-16-2011, 04:48 PM

just installed the parts i had mentioned before...secondary injectors and coil packs and it fixed the car! thanks guys for all the help and now i can enjoy the extra 200hp :)

Great news!

Be careful while enjoying the extra 200hp.
A good running ZR1 can go from 0 to speeding ticket very quickly!!

TomC
'Crabs