'91 L98 coupe, 110K miles, 6 spd

If you rev the car under load (driving), it doesn't want to pull past 3000 RPM. Even revving the engine from idle (no load) several times in a row will cause the engine to lose power and seem like it is going to die.

Things checked:
FP - 43 psi at idle with vac hose on (a bit high, but no AFPR, I thought it should be at 37 with vac on and about 42-44 with vac line disconnected at idle)
timing - 6° with ALDL disconnected (was at 10°, and had the same issues)
TPS - 0.56 (within spec)

Things noted:
MAP sensor connector has been replaced with another pigtail (cheap crimp connectors)
TPS sensor connector has been replaced with another pigtail (again, another cheap repair with nasty wires hanging out)
Coolant level sensor in radiator - sensor present, but nothing connected, just a simple spade sticking out. Not positive that 91 had something connected, but I will assume that it does since the sensor is present.
several vacuum lines are not routed properly, but it looks as if there are no open connections and they do go where they are supposed to.

My initial thoughts were that the injectors might be clogged due to age, but it does not act that way. No codes being set by the computer.

It would appear either electrical or fuel related. The cats may be going as well, as it appears that he has run it for a while fairly rich.

Any thoughts?

Aaron

 

my car does this occasionally, id like to hear too!!

 

I would start by properly fixing all of those jury-rigged things that you noted.

 

Yes, I will purchase the new pigtails, or rob an old harness at the house. My next step will be to ensure that all of the things as stated above are accurate (these were quoted by another shop, and I want to make sure). Then I will check the codes. If no codes, time to pull the plugs. New plugs if necessary (probably either way). Then start more troubleshooting.

Anyone have a pic of a factory 90-91 SD car, as I would be interested to see wher the MAP snesor resides, as it is now mounted on the R passenger rear upper plenum bolt (looks like crap, and may have been done when they did that "nice" re-wire job).

Thanks for the replies, keep them coming.
Aaron

 

sounds like the cat's the cause of your problems, but I'd correct the rich running condition that caused it to fail. Correct the wiring issues (proper pigtails, soldered and seal with heatshrink), then go after the driveability issue. You may have to replace the cat before doing any further diagnostics on the engine as a plugged cat will affect the fuel delivery signals and you could wind up chasing ghosts.

Good luck!

 

I ran across a similiar problem a few years ago with a 88 TPI Trans Am.
The owner (my brother) had complained about the car since he bought it. "It was a dog" was said for many years. I drove the car and just like you say it wouldn't rev much over 4000 rpm. It was very slow getting there as well. My brother removed the cats and it actually got worse.
I asked him when was the last time the fuel filter was changed. You should have seen his face. Uhm...uh...never! At least not for the 5+ years that he owned it!
We changed the filter and went for a ride. The look on my brothers face was priceless! He was very excited at first and then he got this dumb embarrased look. I can't believe that was the problem. Thats all he kept saying over and over. A frigging $5 filter!

My advice is to look at the simple things first. Eliminate them and then move to the next component. It is hard to stick with this principle because humans always go to the absolute worse thing it could be as a starting point.

Maybe you'll be lucky and it will be that $5 fuel filter. Wouldn't that be cool!
Good luck!
John

 

oh...forget the fuel pressure at idle. You have to check it at wide open throttle under load to determine if the filter is clogged or the pump is bad. If I remember correctly the Trans Am maintained pressure under load so the filter could have been overlooked. But for $5 bucks we figured it was money well spent anyway.
Cheers,
John

 

Completely off topic but the phrase is Gerry Rigged. It comes from WWII when the allies referred to the Germans as 'Gerry".

 

I agree with the others on fixing the little things first.

To check your cats, remove pre-cat O2 sensors and rev/drive. This usually opens up the exhaust enough to see the symptoms go away and indicate clogged cats. Just wanted to give you a quick way to diagnose with minimal labor and no cost.

 

I found that the O2 sensor had been disconnected and wire-tied out of the way. At first blush, you might say that this could be the issue, but I read into it that there may be bigger issues, as someone took the time to "semi-permanantly" disconnect the O2.

It definitely serves to identify why it was running rich, but now I wonder if there are truly any codes. Kinda puts the other shops whole diagnosis in question.

Thanks for the thoughts and replies.
Aaron

 

Again with little things - don't overlook the ignition system . Make sure that the correct spark plugs are installed , check the wires , and the spark plug gap . Also look for carbon tracks in the distributor cap and the " button " that connects the coil to the rotor via the metal tab on top of the rotor . Most auto parts chains can test ignition modules too as part of the process of elimination. Good luck

 

Might be worth looking at the egr if it is still present, clogged cats normally(in my experience anyway)cause other symptoms such as overheating and heat through the floorboards.

 

Thanks, I learned something new today.

 

Well, I finally dug into the car today. I shortened the wiring and soldered and heat-shrinked the sensor connectors properly. I set the TPS (was 0.48mV, now 0.56mV) and set the timing (was 10°, now 6°). The car is getting progressively worse, but throwing no codes. I actually spoke to the owner today vs the shop that sent the car to me. The owner has had the car for 18mos, and it has never run real good, but not the bogging that it is currently doing. If you give the car any thing past 1/4 throttle, the car will bog to the point of dieing. Under no load in neatral, you can rev it "very slowly" to about 4K before it starts bogging out.

It has had an O'Reilly long block installed, and they did not keep the aluuminum 113 D-port heads. It now has straight plug iron heads that they claim are off of a TPI camaro. The plug wires contact the manifold and heat shields extensively. The owner has went through three sets of plug wires in the last year. Running "shorty" Accel plugs to help, also "woven sock" heat shields.

The car dies out and would not restart as I was driving out of my street. My son and I puished it back home.

I will check fuel psi tomorrow. Then it is on to the spark. I am wondering if the factory HEI can be "taken down" like an MSD can when one plug wire arcs to ground. Thoughts??? Would the shorted plug wires have taken out the module? Wouldn't this set a code?

Thoughts on plan of attack welcomed.

Thanks,
Aaron

 

After you are positive it is getting fuel. Check the spark and make sure it is good. I had a coil wire burn up under the cap and it would run only at idle. The under load comment that you made screams out spark!
Unfortunately you are getting someone elses handy work. I wonder if they put the distributor in correctly?
Man I feel for you on this project! Someone screwed the guy out of 113 heads! Too bad!

Good luck on this one!
John

 

Exhaust is blocked up. Get an exhaust back pressure gauge. They screw into the 02 bung. Everybody should have one. Screw it in, start the car, give it gas, and see what it goes to. Anything over about 1.5 PSI under snap throttle, or heavy accel is too much. I'll bet yours pegs a 15 PSI gauge.
Anotherway to tell is if it looses vacuum under load.

 

Also check those spark plug terminals. I had the accels and on more than one the screw-on brass tips became loose. May be a stretch but check if you have the right lengh plugs in there as well.

 

That's the factory spot for the MAP Aaron...

Good luck!

Doug

 

Yep....clogged up cats. Had that on a Quad 4 some years back. She ran fine at idle, but had no acceleration.

 

"Jerry rig" is indeed from WWII as you say but it was a bastardization of the much older term "Jury rig" which means the same thing.

The term "jury" is believed to have its source in a Latin and Old French root meaning "aid" or "succour".

Oh and it's Jerry with a J not a G. Jerry = German. "Those Jerries are up to something. I can hear the 88's!"