No power at all at speed (1988 C4)

[joatrash]

Hello all,
I'm trying to help my mechanic diagnose the following problem:

I have absolutely NO power when running at speed on the highway (RPMs over 1500). Hitting the throttle will do very little... the engine revs, but it seems that the transmission doesn't want to respond or seems like it "doesn't know what to do". However, the transmission has been taken down and looked at and there was nothing wrong there so it has been ruled out as the culprit.

The car was also recently starting to show an intermittent CODE 44 (SES would come and go while driving) so we are now looking into the fuel delivery/mixture system. The following are current symptoms:

- unnaturally high fuel consumption (about 1/3 more than what is "normal" for a healthy L98)
- perfect cold start, delayed (3-4 seconds) warm start, with accompanying heavy gasoline smell in the latter case
- The 02 sensor WAS bad and has now been replaced. (the car was not entering closed loop before, but it does now)
- good idle and ok driveability at low speeds
- TPS has been checked and is ok
- idle and low revs seem to be pretty stable
- as stated above... she has NO power. I can get her up to highway speed but it takes forever. Feels like she's got 10Hp!
- fuel pressure was apparently rather low. I don't have the exact value but it was not the 42-55 that's supposed to be there.

I've had the car for a couple years and the delayed start and high fuel consumption has been there all along. I assumed that the injectors might be getting bad and after 70K miles so I was counting on needing to replace them soon. However, the POWER has always been there before, up until a couple weeks ago when I was out driving and suddenly all the power was gone. At this point everything seems to be screaming "INJECTORS" but since that's a fairly costly replacement, I thought I'd check in here first. Perhaps the fuel pump or filter? Vacuum leak?

Any tips appreciated. Hop y'all are enjoying your summer.

THANKS!
//Joe

 

[John Robinson]

I think your on the right track with the fuel pump and filter. They may need cleaning or replacement.

Another possible cause is the fuel. When this started had you just filled up with fuel? And if so are you still running on that tank of fuel? This sudden onset of poor performance suggest to me that you may have gotten into some bad fuel. I have had this happen before.

 

[joatrash]

Hi John and thanks for the input. I've filled up a couple times on fuel so that's probably not the cause. I'm waiting for some more trouble-shooting info right now.

 

[joatrash]

Hmm. Ok. Fuel pressure is apparently 35-45 and was compared with another Vette that had the same value. So that might not be it.

Perhaps an ignition timing problem? A computer problem? My guy is going to disconnect the MAF and see what happens. He's a bit puzzled by the strong gasoline smell when she starts up warm... can't find any apparent leaks (and I know that the exhaust system is whole because that has been checked before).

(The irony of this whole thing is that if it WERE the transmission that needed rebuilding it would have been fixed by now... because the car is with a transmission expert. He just doesn't know the L98 by heart. Not that many people here do.)

Maybe we'll just have to take off the rails and go for the injectors after all.

 

[Hib Halverson]

So far, it's not clear in this thread whether or not the fuel filter has been replaced. Has it? DTC44 is for lean exhaust, so, clearly, you have a fuel system problem somewhere.

It's also possible the cat convertor is restricted or "plugged-up" but the first place I'd be looking for trouble is with the fuel system.

Do you have the 1988 Factory Service Manual?

 

[boomdriver]

Cats bad....

if it were a bad fuel filter or pump there were be a bunch of burping backfiring and bucking as throttle was applied since fuel was unavailable. The excessive fuel use tells us that the fuel IS flowing somewhere. Its the exhaust thats got the problem.

get a new cat, problem solved.

Test by pulling the 02 sensor and feeling the pressure that exits. The max allowable is only 2-3 psi. If the exhaust blows out of the o2 sensor hole...its the cat gaurenteed.

unless someone stuffed a potato in the exhaust tips...

(never done that myself, I always use expanding foam sealant to "silence" an obnoxious ricer or somebody that screws me in the parking lots...)

 

[joatrash]

The filter has not been replaced but pressure is steady. (The DTC 44 seems to have gone away with the new O2 sensor)

We're going to check the cat next. My guy was already thinking along those lines because she runs ok on low revs and speed. Thanks for the tips again all! Will keep updating as I get any news.

 

[John Robinson]

Dont forget about the EVAP system causing the fuel smell. Before you do anything else you must find the source of the fuel smell. Check all the fuel line connections. If it has the quick disconnect fittings check for bad O Rings. About 6 weeks ago I had a fuel smell and then all of a sudden the car was stumbling and not running smooth. I turned around and drove the mile back home and when I got there I had gas pooled all over the engine compartment. The problem was with the fuel rail fuel lines. One of the O rings on the crossover fuel lines between the rails had totally broken up. After I fixed the leak and started the car I noticed that over 1/4 tank of gas had been sprayed all over my engine while I drove it home. There have been several cars posted over the years that burned up. A fuel smell is a very serious thing and must take priority over everything else.

 

[joatrash]

The fuel smell has been there for while- long before the "no power" issue reared up, so that might actually be a separate thing. But I haven't found the cause yet, except it possibly being the cold-start valve, which is a little bit "damp". Idle and low-revs running seems fine and pretty stable- it feels like there is low-end power when driving real slow but as soon as she cranks up that is when nothing happens. Checking the Cat... stay tuned!

 

[Hib Halverson]

The filter has not been replaced but pressure is steady. (The DTC 44 seems to have gone away with the new O2 sensor)

Have you run the fuel pressure tests in the Service Manual? If so, did the fuel supply system pass that test?

We're going to check the cat next. My guy was already thinking along those lines because she runs ok on low revs and speed. Thanks for the tips again all! Will keep updating as I get any news.

If I had an 88 that exhibited those systems and had no problem with misfire, I'd first look at either fuel supply or restricted exhaust.

 

[Jeb]

Have you run the fuel pressure tests in the Service Manual? If so, did the fuel supply system pass that test?



If I had an 88 that exhibited those systems and had no problem with misfire, I'd first look at either fuel supply or restricted exhaust.

My 87 exhibited the exact same symptoms.

Check the exhaust system. The pre-cats or cat may have collapsed blocking the exhaust. I changed mine out and that took care of it.

 

[joatrash]

My mechanic is checking the cats tomorrow. Does the 88 have pre-cats and one main?

You know... I just though of something. Last year, I had another mechanic friend chasing what SOUNDED like an exhaust leak coming from somewhere near the front end on the right side. It was kind of a metallic "chuffing" sound, like a small steam train. The sound would more or less disappear when the engine got warm. He went over the entire system but found no leaks anywhere. Now I'm wondering if that sound was in fact coming from the cat as is was on the verge of breaking down... because I haven't heard the sound at all the last couple of months....

 

[Hib Halverson]

I don't think 88s have pup cats but if they do, cut them off. They only exist to the car could pass the FTP emissions test. They're not needed for the emissions tests or "Smog Checks" some States require.

 

[joatrash]

I don't think 88s have pup cats but if they do, cut them off. They only exist to the car could pass the FTP emissions test. They're not needed for the emissions tests or "Smog Checks" some States require.

Well, I'm in Sweden (car is imported from the US though) so I don't have to worry about smog regs on your side of the pond! It's actually kinda funny... Sweden has pretty strict smog regs too, but for vehicles that were imported up to and including 1988 as "a relocation item" (i.e. if a Swede has been in the US for a year or two and has had the car during that time), they are allowed to essentially bypass ALL those regs more or less. They are also allowed to keep the all-red rear lights and turn signals, which is pretty sought after, because all european-sold Vettes have two red and two ORANGE tail lights.

 

[boomdriver]

My mechanic is checking the cats tomorrow. Does the 88 have pre-cats and one main?

You know... I just though of something. Last year, I had another mechanic friend chasing what SOUNDED like an exhaust leak coming from somewhere near the front end on the right side. It was kind of a metallic "chuffing" sound, like a small steam train. The sound would more or less disappear when the engine got warm. He went over the entire system but found no leaks anywhere. Now I'm wondering if that sound was in fact coming from the cat as is was on the verge of breaking down... because I haven't heard the sound at all the last couple of months....

The 88 does not have the pre-cat or "pup-cats"...that was only thru 87.

That exhaust leak is likely the EGR tube or valve leaking the gases that are diverted to the intake. The EGR only allows the gases to enter after warmup. I have a similar leak that I only hear after it warms. Pretty sure its an EGR issue as no other leaks are making themselves obvious.

Cats can fail in one of 2 ways...
they can burn out, where the thing gets so hot from having a rich exhaust that causes the chemical reaction to get out of control and melt the substrate off the honeycomb inside, therefore killing the ability to react with gases, or they can plug up with carbon caked on the weakened or old style cat. Older cats were like bricks and were more restrictive but they clogged easily. Some were like boxes of pellets that the gases filtered thru. Newer cats have a more free flow design where there is just as much chemical surface area for gases to pass over but not so tight that they plug up as easy. Usually new style cats melt and die. Evidence of this can be seen by discoloration around the cat entrance side that should be cooler than the exit side. I've seen one get bright red hot...scared the crap out of me wondering how the car did'nt burn to the ground from the heat that was radiating from that shoe box size glowing hot converter.

 

[jpushard]

Cats

On my 89 the left bank cat came apart and blocked off my resonator so the exhaust was blocked.
I cut the exhaust right behind both cats knocked out the rest of insides, that made them hallow then
I replaced the resonator with a straight pipe. Now from a corvette that would not spin a tire to one
that bakes them right off. All kinds of new found power. Good Luck Jeff

 

[muddywaters]

The 88 does not have the pre-cat or "pup-cats"...that was only thru 87.

That exhaust leak is likely the EGR tube or valve leaking the gases that are diverted to the intake. The EGR only allows the gases to enter after warmup. I have a similar leak that I only hear after it warms. Pretty sure its an EGR issue as no other leaks are making themselves obvious.

Cats can fail in one of 2 ways...
they can burn out, where the thing gets so hot from having a rich exhaust that causes the chemical reaction to get out of control and melt the substrate off the honeycomb inside, therefore killing the ability to react with gases, or they can plug up with carbon caked on the weakened or old style cat. Older cats were like bricks and were more restrictive but they clogged easily. Some were like boxes of pellets that the gases filtered thru. Newer cats have a more free flow design where there is just as much chemical surface area for gases to pass over but not so tight that they plug up as easy. Usually new style cats melt and die. Evidence of this can be seen by discoloration around the cat entrance side that should be cooler than the exit side. I've seen one get bright red hot...scared the crap out of me wondering how the car did'nt burn to the ground from the heat that was radiating from that shoe box size glowing hot converter.

I have an 88 and it has pup cats and a main. I had the raw fuel smell and it was the leaking injectors.

 

[Airship]

Check your main Cat for obstructions. 1988 Corvettes have three Cats, two small "pre" cats and one big main. The substrate inside the two pre cats breaks down after years of heat cycles, vibration and crumbles, clogging the main cat so your exhaust will be restricted. This causes the power loss because your engine is basically an air pump and the exhaust is now pressurized and has no where to go. The symtoms are exactly as you descibe.

 

[muddywaters]

Check your main Cat for obstructions. 1988 Corvettes have three Cats, two small "pre" cats and one big main. The substrate inside the two pre cats breaks down after years of heat cycles, vibration and crumbles, clogging the main cat so your exhaust will be restricted. This causes the power loss because your engine is basically an air pump and the exhaust is now pressurized and has no where to go. The symtoms are exactly as you descibe.

We'll have to check that too. Ah, The Hindenberg(Avatar) Disaster. A flying bomb, with people underneath it, it was pretty obvious after it happened. Kind of like OBL Kamikazee'ing the US, that was obvious too after it happened. It's been done before in history. Getting back to the 88's, makes since to take a look at the main cat for blockage, I've done everything else.

 

[boomdriver]

I have an 88 and it has pup cats and a main. I had the raw fuel smell and it was the leaking injectors.

My mistake....

I thought that the pre-cats ended in 87....

Now to figure out if its CRS or just wrong...:ugh