87 C4 Engine Cuts Out When Floored
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
87 C4 Engine Cuts Out When Floored
Hello All,
I'm new to this forum and just recently bought a 87 C4. The car is completely original, but had a small miss at idle, hard to start and the engine would cut out when it was floored while I was driving.
I decided to give it a through tune up with the following parts:
Air, Oil, and Fuel Filters (Changed Oil)
Cap, Rotor, Wires, Spark Plugs and adjusted engine Timing
PCV Valve
Cleaned Throttle Body
After I replaced all these parts the car started better, but it still had the miss and the engine cut out.
I checked for trouble codes and got a 34, so I decided to go ahead and replace the the MAF relays. The idle did get better and no more code 34.
I checked the fuel pressure and it was 37 - 38 psi at idle and the pressure never dropped when the engine would cut out.
Any suggestions?
Thanks,
Henry
I'm new to this forum and just recently bought a 87 C4. The car is completely original, but had a small miss at idle, hard to start and the engine would cut out when it was floored while I was driving.
I decided to give it a through tune up with the following parts:
Air, Oil, and Fuel Filters (Changed Oil)
Cap, Rotor, Wires, Spark Plugs and adjusted engine Timing
PCV Valve
Cleaned Throttle Body
After I replaced all these parts the car started better, but it still had the miss and the engine cut out.
I checked for trouble codes and got a 34, so I decided to go ahead and replace the the MAF relays. The idle did get better and no more code 34.
I checked the fuel pressure and it was 37 - 38 psi at idle and the pressure never dropped when the engine would cut out.
Any suggestions?
Thanks,
Henry
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Will it do it at idle and when driving? Could be a dead spot in the TPS (throttle position sensor). If you have an old analog ohm meter you can check it readily. Disconnect the harness from the TPS and put your leads on the top 2 pins on the sensor (NOT the harness). Set the meter to a low setting like 20 ohms and while watching the meter's needle, open the throttle in a smooth motion. If the needle starts jumping around or reads max ohms (infinity) during the operation of the throttle...replace the sensor.
If that all checks good, you could be dropping spark at the higher RPMs...ignition module, primary or secondary coil, reluctor ring loose, corroded or broken, bad ground somewhere....
If that all checks good, you could be dropping spark at the higher RPMs...ignition module, primary or secondary coil, reluctor ring loose, corroded or broken, bad ground somewhere....
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Morley,
It only does it when the car is driving.
I just remembered something, it originally started to do it when the car was turning and I accelerated hard, but now it does it whenever the car is punched (In drive from a standing start or while moving).
It won't do it in Park.
I'll check the TPS and all the other parts you pointed out.
I'm starting to think it may be a ground issue, like you suggested.
Does anyone know the location of the engine grounds?
Thanks,
It only does it when the car is driving.
I just remembered something, it originally started to do it when the car was turning and I accelerated hard, but now it does it whenever the car is punched (In drive from a standing start or while moving).
It won't do it in Park.
I'll check the TPS and all the other parts you pointed out.
I'm starting to think it may be a ground issue, like you suggested.
Does anyone know the location of the engine grounds?
Thanks,
Le Mans Master
Joined: Oct 2003
Posts: 6,130
Likes: 2
From: seattle WA
There are alot of grounds on an 87-but, start by checking your battery ground and terminals, then you could check the ground strap that connects behind the drivers side cylinder head. I believe there's another ground strap down on the frame by the battery-just from memory-what little I have left lol. You may want to test the TPS-hope you have a manual.And you may want to check for vacumn leaks-the old vacumn lines (plastic) crack over time with heat etc. oops-I see Morley suggested the TPS-see what I mean about memory lol.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
Originally Posted by 87capevette
I just remembered something, it originally started to do it when the car was turning and I accelerated hard,
but now it does it whenever the car is punched
but now it does it whenever the car is punched
The fuel tank does not have any baffles, so to keep the inlet submerged, one must have enough fuel on board to maintain submersion.
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Rick,
I'll check the ground locations you pointed out and come to think of it I do hear what sounds like a vacuum leak coming from the back of the engine. I did the old test of spraying carb cleaner around the area of the sound, but there was no change in the idle. Does anyone know what should the vacuum be at idle?
Mikey,
Yes, I did un-plug the EST, put the car in Drive and set it to 6*BTDC. It was originally 8*ATDC and would crank several times before it would eventually start.
JrRifle,
When it first happened I thought the gauge was reading incorrectly and it was very low on fuel, so I topped off the tank. Unfortunately It continued to occur during turns and now everytime during wide open throttle. It only does it when the car is in Drive, but if it is Park I can rev up & down the engine with no problems. I attached a FP gauge, but the pressure stays steady during idle & when the engine cuts out.
I'll check the ground locations you pointed out and come to think of it I do hear what sounds like a vacuum leak coming from the back of the engine. I did the old test of spraying carb cleaner around the area of the sound, but there was no change in the idle. Does anyone know what should the vacuum be at idle?
Mikey,
Yes, I did un-plug the EST, put the car in Drive and set it to 6*BTDC. It was originally 8*ATDC and would crank several times before it would eventually start.
JrRifle,
When it first happened I thought the gauge was reading incorrectly and it was very low on fuel, so I topped off the tank. Unfortunately It continued to occur during turns and now everytime during wide open throttle. It only does it when the car is in Drive, but if it is Park I can rev up & down the engine with no problems. I attached a FP gauge, but the pressure stays steady during idle & when the engine cuts out.
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Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Rick,
I'll try it with propane, that's a new one for me?
I have the day off today, so I'll go ahead and put the car on my lift and check everything everybody suggested.
Coincidently, I have a 87 Grand National and it idles just like the Vette. I guess it's a 80's GM thing?
Thanks for all the info everyone and keep the suggestions coming in!
I'll try it with propane, that's a new one for me?
I have the day off today, so I'll go ahead and put the car on my lift and check everything everybody suggested.
Coincidently, I have a 87 Grand National and it idles just like the Vette. I guess it's a 80's GM thing?
Thanks for all the info everyone and keep the suggestions coming in!
Burning Brakes
Joined: Jun 2004
Posts: 752
Likes: 0
From: richardson tx
87capevette seems we are having exactly the same problem. togather hopefully it will get figured out. heres what iv done per fourm members suggestions pryor to reading this post. morley, did replace my tps no change. whipreck, havent checked the timing on mine in a while mine was set on 24. jrriflecoach, taped a fuel pressure guage to the windshield no change. slamin1, please dont let it be an injector as you cant get to most of them with the super ram in the way not trying to be rude but that will be my last hope. thanks for the tip. jonecap, my converter is gutted. redeasysport, just tryed the egr vacum a couple of days ago no change. 87capvette at this point im leaning towards plug wires plugs cap rotor maybe coil. but as you stated you just replaced all of yours during the tune up mine are about 3 or 4 months old all msd with exception of the plugs which are autolight. if for some reason i lose your post and you figure it out or if i do i want to leave my email steve1ph2@comcast.net. thanks
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Slamin1 - I haven't had time to test the injectors, but does anyone know what should be the correct ohm range for my injectors?
Jonecap - I forgot to mention, I had to empty out the large center cat because the inside ceramic type material began to rattle really bad. It still has the 2 smaller cats up front. Are these prone to failure like the larger center one?
Redeasysport - I'll try the egr test you suggested. If I apply vacuum to to the egr it should hold?
Steve1ph2 - I'll keep you updated. If everything checks out OK then i'm leaning towards a faulty module
I did have time yesterday to check the 2 ground locations Rick Lambert suggested (Drivers-side engine block & ground strap to frame by battery). I removed, cleaned and re-installed the grounds, but the problem still continues. It did fix the small flickering my dash and light system had. Thanks Rick!
Thanks All
Jonecap - I forgot to mention, I had to empty out the large center cat because the inside ceramic type material began to rattle really bad. It still has the 2 smaller cats up front. Are these prone to failure like the larger center one?
Redeasysport - I'll try the egr test you suggested. If I apply vacuum to to the egr it should hold?
Steve1ph2 - I'll keep you updated. If everything checks out OK then i'm leaning towards a faulty module
I did have time yesterday to check the 2 ground locations Rick Lambert suggested (Drivers-side engine block & ground strap to frame by battery). I removed, cleaned and re-installed the grounds, but the problem still continues. It did fix the small flickering my dash and light system had. Thanks Rick!
Thanks All
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
If your using a mightyvac to test the EGR put a good vacuum to it and it should bleed off slowly ~20sec
On the injectors~14ohms but it is more important that they all read around the same.
On the injectors~14ohms but it is more important that they all read around the same.
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Redeasysport - I'll have to wait until tomorrow to test the injectors, because the battery in my digital multimeter was dead
I did find two interesting problems on the car today:
1 - I applied vacuum to the EGR valve and it would not hold any vacuum at all. I used my Sunpro hand held vacuum pump with a built in gauge. So does this mean the EGR valve is bad and must be replaced? I plugged the vacuum line that attaches to it and took the car for a spin, but it still does the same thing.
2 - I discovered that a small round vacuum check-valve towards the back of the engine, near the distributor, had a small hole in it. I went ahead and replaced it with a vacuum tee, until I can buy a new one tomorrow. The car idled a little bit better, but it still cuts out under full throttle.
Lastly, I paid close attention when the engine would cut-out and I could hear small backfires coming from the intake (throttle body)
side of the motor. I'm thinking this would point me more in the direction of a ignition problem instead of a fuel problem?
Thanks
I did find two interesting problems on the car today:
1 - I applied vacuum to the EGR valve and it would not hold any vacuum at all. I used my Sunpro hand held vacuum pump with a built in gauge. So does this mean the EGR valve is bad and must be replaced? I plugged the vacuum line that attaches to it and took the car for a spin, but it still does the same thing.
2 - I discovered that a small round vacuum check-valve towards the back of the engine, near the distributor, had a small hole in it. I went ahead and replaced it with a vacuum tee, until I can buy a new one tomorrow. The car idled a little bit better, but it still cuts out under full throttle.
Lastly, I paid close attention when the engine would cut-out and I could hear small backfires coming from the intake (throttle body)
side of the motor. I'm thinking this would point me more in the direction of a ignition problem instead of a fuel problem?
Thanks
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
It does sound like the EGR is not working correctly.It should bleed off gradually when a vac is applied Around 20sec give or take.Less than 5sec I would replace it.
I had 5000 knocks in my engine in 5 min caused by a bad EGR.You would be suprised what vacuum leaks can do.I would also check your intake vacuum level.Mine is a LT1 and I am pulling 20inHg at idle.Keep looking for vacuum leaks.You can use starting fluid to help.
I had 5000 knocks in my engine in 5 min caused by a bad EGR.You would be suprised what vacuum leaks can do.I would also check your intake vacuum level.Mine is a LT1 and I am pulling 20inHg at idle.Keep looking for vacuum leaks.You can use starting fluid to help.
Thread Starter
Heel & Toe
Joined: Dec 2005
Posts: 21
Likes: 0
From: Cape Coral Florida
Redeasysport - I just tested the injectors and they were between 16.4 - 16.6 ohm and I also tested the TPS sensor and it was .540 at idle. I think both readings were within spec? I also replaced the vacuum check valve from yesterday and checked to see if there was any play with the distributor gear. It all checked out ok and I continue to have the same problem. Out of everything I checked only the EGR valve seems to be bad. I tested it again today and it still won't hold any vacuum. Can a bad EGR be my problem?
Thanks
Thanks
Burning Brakes
Joined: Nov 2005
Posts: 848
Likes: 1
From: 1992 LT1 6 speed Cayman Islands
Ignition problem
Your EGR is obviously bad and is causing some kind of a vacoum leak and is probably responsible for any roughness in your idle and some loss of power and should be replaced.
However I do not think that this is the cause of the engine cutting out at WOT.
I think the cutting out at speed is definately an ignition problem. I had almost the exact same problem except sometimes the engine would not start back up right away as the problem got worst.
My problem was a bad connection on the ignition module.(see my post " 1992 wont start" - I have an LT1 with Opti)
Check all of the connections between the ECM and and the Distributer (do you have Opti?) and coil.
Give these connections a shake at idle to see if you cah recreate the problem, if you can you have found the problem. A bad connection would also account for the pop you are hearing in the manigold when the car shuts out as making and braking the connection will cause the coil to spark at the wrong time.
It could also be an ignition module going bad and just not able to handle the extra work at high RPM.
Hope this helps
Jerris
However I do not think that this is the cause of the engine cutting out at WOT.
I think the cutting out at speed is definately an ignition problem. I had almost the exact same problem except sometimes the engine would not start back up right away as the problem got worst.
My problem was a bad connection on the ignition module.(see my post " 1992 wont start" - I have an LT1 with Opti)
Check all of the connections between the ECM and and the Distributer (do you have Opti?) and coil.
Give these connections a shake at idle to see if you cah recreate the problem, if you can you have found the problem. A bad connection would also account for the pop you are hearing in the manigold when the car shuts out as making and braking the connection will cause the coil to spark at the wrong time.
It could also be an ignition module going bad and just not able to handle the extra work at high RPM.
Hope this helps
Jerris
Last edited by Jerris; Jan 18, 2006 at 11:08 PM.
Burning Brakes
Joined: Nov 2005
Posts: 1,211
Likes: 2
From: Dumas Arkansas
I've had this same problem at WOT. When I get about 100mph it stutters and seems like it's not getting any gas. But once I get about 110mph it quits for some reason. I rarely ever get above 120. It all depends if numbnutts is still wanting to test the Vette. 
I'm looking at the ecklers catalouge at the EGR Valves for a 92 automatic and see that there 60 bucks so I'll probably get me one of those too why I'm order happy lately. Their EGR Vacuum Check Valve is for 1985-90. So I guess my 92 doesn't have this option?
I'm looking at the ecklers catalouge at the EGR Valves for a 92 automatic and see that there 60 bucks so I'll probably get me one of those too why I'm order happy lately. Their EGR Vacuum Check Valve is for 1985-90. So I guess my 92 doesn't have this option?