I think this is a great site, and this is my first post.

My son and I are restoring an 87 IROC Z-28, 305 TPI, that has been put together from a couple of cars.

Most of the time the car runs great, but there has been a problem ever since we got it together, and seems to be getting worse, but also is aggravatingly intermittent.

The error codes we are getting are 33 AND 34 at the same time. Sometimes after a reset, it might just be code 33, but most of the time it is both of them. I know it is MAF sensor, but the codes together are opposite each other.

It will be running great on the highway, and all of a sudden the engine light will come on and it will start running rough (lacks horsepower). My son will unplug the TPS and reinsert it and it seems to run better for awhile, but this is happening with more frequency.

Between taking it to mechanics and ourselves we have changed out 2 MAF sensors (which makes this the third since the original),
the TPS, fuel filter; we have gone through and checked the wiring around the MAF sensor, and can't find any vacuum leaks.

Is there something we are missing? Another thing, it doesn't seem to happen when he drives to school in the morning (6 miles) but happens almost immediately on the way home, seemingly having to do more with the air temperature than the running temperature of the car.

Any thoughts or help would be appreciated.

 

MAF gets power thru a relay, not uncommon for the relay to get intermittent. Generally there are 2 relays, one for power and one for MAF burnoff to clean the hotwire. Not sure in 87 if they are by the ECM mounting or on the firewall but suspect the power relay first.

 

Not sure if this will help but ...

I had a 87 GTA 305 TPI, and after a coolant leak that sprayed all over the engine, had similar problems. Tried the same things as you, in the end it was the distributor, took about a year and 3 different dealers to find the problem.

Worth looking into anyway.

 

I had just about decided to go after the relays next. They are on the firewall, Danno. Do you know which are which? The middle one (there are three) is marked MAF power. I think the other two are the MAF burn off and fuel pump, but they are not marked and I can't seem to find a diagram for them.

Canadamaro, was it the distributor cap you replaced or the whole distributor? The distributor cap was loose, so we tightened it. I thought that would probably get it, but it didn't. My son and his friend done most of it up to that point, and his friend is a pretty good mechanic. The distributor cap and wires look fairly new, but I had thought about going after them if the relays didn't take care of it.

I have had the car in the shop several times, and they would come to the conclusion that its this or that and replace something. I finally decided we could save money and replace parts ***** nilly ourselves.

Thanks.

 

Fuel pump relay is the different looking one of the three. The 2 oval shaped ones are power ond burnoff. While it's running tap them with the handle of a screwdriver, lots of times the engine will stumble and throw a code. The 2 relays are the same part number, replace them both if I were you. They are at least in 89 the same part number as the fan relays and they has lots of problems with them being intermittent. The newer GM part is a redesigned unit as is the NAPA replacement.

 

Being an 87 they should be square/rectangular not oval. There should be 3 in a row,the MAF power is the one closest to the motor or the first one on the left fastned to a bracket that sticks out from the firewall with a flat multi wire connector behind it.

I live rite outside Madison,IN and could come look at it if replaceing the relay doesn't help.

If you take it to a mechanic in Madison or Scottsburg you'll be wasteing money. Theres not any that know **** about TPI.

 

Today we replaced the relays (we had to order them). It did not change anything.

One thing of note, Saturday we swapped the two old relays, without any luck. But when I had taken the MAF power relay down from the firewall, when we put in the jumpers the coolant fan came on.

On looking at the connector for the relay, the wires on the A and B terminals on the connector had about a half inch of bare wire sticking out from the connector, which is enough to allow them to short each other. We isolated the wires with black tape, but I am wondering if there is a bad connection inside the connector itself.

I have some new connections, and will try those next. Also, I got a schematic of the relay, and I have some of the GM stuff from this site, just to compare an make sure someone didn't get wires swapped.

The problem seems to happen after things warm up to the point that the computer switches from closed loop to open loop mode.

 

I was a little vague in the previous post.

We had put the jumpers in the ALDL and when the ignition was turned to on, the coolant fan came on, which is unusual. That was how I found the wires in the connector were bare and shorting.

I appreciate the comments so far, and if anyone can think of anything else it would be much appreciated.

Transambill, I know what you mean about the mechanics in this area. TPI seems to be a special animal.

 

The fan comming on when you jump the A&B terminals is normal.
Are you sure the MAF sensor is good? When I replaced mine I went thru 3 of them from AutoZone before I got a good one.

 

That is a scary thought. So far we have been through 2 of them. The one I got from NAPA was the first, and another mechanic did the second one- it is a remanufactured one but I don't know where he got it.

Found out later the NAPA MAF was still under warranty, could have just brought it back and exchanged it. I guess I will try to sift through the info on this site and see about checking it.

The MAF runs on a 5 volt reference from the ECM and I am starting to wonder about that now, too.

Thanks.

 

I have a parts car, which is an 88 IROC. I don't have an engine in it and some of the sensors that are left are not the same as what is in the 87.

What I do have in the parts car is an ECM. I know the PROM has to be changed from one to the other. Does anyone know if the ECM is interchangeable from one car to the other?

If I could swap them and still get the same problem, that would at least rule out the problem being the ECM.

Went through a bunch of connections today, put in new connectors, etc., just to be sure that resistance in a connector somewhere wasn't causing the trouble- still no luck.