My '87 IROC was running just fine now all of a sudden, it doesn't want to run hard. It acts like there is a limiter on the thing. Try to rev fast in 1st or 2nd and it will hit a point where it just dogs out and wont rev anymore. Do the same in 4th or 5th and it seems to pull but will not rev its normal manner. Put a fuel pressure gauge on it and its running 41 to 45 psi on the rail while im driving. I had the gauge on sticking out the back of the hood to check while I drove. Changed fuel filter and it wasn't bad, no change. It is really acting like the computer is limiting it in some way. Anyone got an idea on this funny (not funny) problem. Thanks for ANY help.

 

clogged cat?

 

I would think that maybe, but no cat on the car. Been removed for about 24 yrs. Muffler seems fine. It will "buck" when it starts to hit the rpm band and acts like a speed limiter would feel like. It has a Hypertech stage 2 chip in it, but it is very old, almost as old as the car. This use to happen when I would go for a top end burst at about 130 or so. ?????

 

Try unplugging the MAF sensor and see if it makes a difference. If so you need to diagnose the MAF issue. Maybe just clean it.

 

I will give that a try when I get home tonight. Would the car run good if i were unplugged? It just came out of paint and the "y" intake that has the MAF on it may not be plugged in, that just came to me after seeing my buddy put it back on the car, I'm not sure he hooked it up. Hmmm again. And thanks alot. :-)

 

The car will run on back up fuel MAP with the MAF unplugged. If the rest of the engine is okay, it should run have decent.

 

What would you use to clean the MAF with, carb spray, soap and water??? I don't want to ruin it if it is ok. Maybe it has some paint overspray on it. It was in the paint shop but not on the car at the time of priming and painting.

 

It did run decent. I had a "tuner" car pull up next to me for a little run and it ran fine, but shortly after that burst, it started the "bucking and stalling" thing. I bet we forgot to hook the MAF back up, but am not sure since I didn't put it on, my paint shop buddy did. I sure appreciate you guys on the forum!!! Thanks for the ideas. If you have any others, post them and I will check everything.

 

Use MAF Sensor Cleaner only. No water and no carb cleaner.

 

they make a maf and sensor cleaner that you can buy at the auto supply store that is safe on your components and honestly ive used it before and it works well just take it off before you do it, dont spray it into the engine while running... also make sure the element isnt covered in primer or paint over spray...

 

Thanks ASE doc. I might have ruined it!!!

 

Brake cleaner, have been using it for decades, never a problem.

 

Brake cleaner should be fine. MAF Cleaner is just electronic cleaner like QD. It's gentle and won't harm the plastic and seals. I use it because I'm always working on other peoples cars and don't want to be responsible for damaging them. Heck, my car doesn't even have a MAF sensor.

 

I sure hope its just a silly little oversight on my part when we put the air breather assembly back on, that would really make my day. I worked all weekend long trying and testing everything i could think of. I will post tomorrow or tonight the results. Thanks soooo much to you all that had a interest in my problem!!! I have Brake Cleaner on the shelf. I really imagine that it is just not hooked up, but it definately could have paint overspray on the little wires, so I will clean it anyway. :-)

 

For couriosity, what do you use in place of the MAF? I've seen plenty of guys with TPI units and a K&N on the front, just didn't know to work without it.

 

Those are speed density systems

 

Switch to speed density fuel management instead of MAF. GM went to Speed Density in '90 on the 3rd gens. My car is a creature of my own twisted imagination and uses an ACCEL DFI system which is speed density.

 

Is it much to convert it to Speed Density? I've done all kinds of conversions, but usually they go backward to the "old school" days.

 

There are a couple of ways to do it. Buy an ECM and harness from a 90 or newer 3rd gen, or install a complete stand alone system like the ACCEL DFI. Moving away from MAF allows more flexibility in engine design without the MAF restriction in the intake. Unless you're going to go extreme with the engine, it's not really worth the expense and time involved.

 

Well I'm not getting too far away from stock on this one, it's one of the 87 'verts and is a TPI/5 speed car. Just thought I'd ask because the son and I do lots of different things to these cars, but like I said earlier, most of it uses old school stuff and we completely go around the computer. Thanks!!!!

 

Ok so it wasn't just the MAF unplugged, it was plugged in. I haven't cleaned it yet, but if cleaning it doesn't change anything does anyone have any other ideas??? I changed the fuel filter on it and there was nothing wrong with it. It sure has me puzzled. I don't really depend on my local Chevy garage but, might have to have it diagnosed out there. HELP PLEASE. Thanks.

 

If it's not the MAF, it's going to be in the distributor. In fact most certainly the ignition module.

 

Well I rebuilt the distributor last night and it needed it, green corrosion everywhere, but the darn thing still has a surging. My son has much better hearing than me, and he heard a vacuum leak like others describe and it was at the vacuum can. We plugged off all the leaks we could find, but the engine, while holding the thottle in one position will surge up and then down, then up then down. I am going to replace all the vacuum lines that I can find are bad tonight and will report again tomorrow. Its strange, but it can't be anything too big cause it was running fine against that little tuner car that wanted to go for a run. Right after that is when it started messing up. Thanks again, keep you posted. :-)

 

The surging sounds like fuel starvation. Id like to see you monitor O2 sensor data on a scanner while you drive the car and see what it does at full throttle. O2 at full thottle should go rich, as high as .950 and stay there until you let off the gas or the engine passes the top of it's power band at 5,500rpm. If the O2 goes lean at full throttle, that points to a fuel issue, again like the MAF, but it could also be injectors or fuel pressure loss. A pressure guage taped to the windsheild would help find that.

 

I've done the fuel pressure test. On the rail it is 40-45. With the vacuum line pulled on the regulator, it runs full 45 all the time, even when it is messing up. I drove it with the guage hooked up and it never waivered at all - 45 psi. I can hold the thottle in one position and the engine will want to rev, then kinda stall, then pickup more, but then stall again. I am checking every vacuum line coming off of the motor tomorrow (pretty busy today) since my son heard one of the vacuum canisters lines sucking. It had come off of the can, so I put it back on, but I am thinking about killing the power to the car by unhooking the battery for a while, then putting it back on and start it to see if anything has changed. I would bet it is something real simple that I have overlooked. All new distributor internals and cap and rotor, new fuel filter, plenty of pressure to the injectors. Some day I will get it figured out and I sure appreciate all the suggestions, and I'm tryin them all. Thanks ASE doc!!!

 

Maybe computer or chip problem? It did this to me a couple times when I was running it at high speed (130 or so) and I thought maybe it had a speed limiter in the chip. Now it seems like the same problem, but at much lower speeds and rpm's

 

I would take a look at your catalytic converter. I just replaced mine, and wow, what a difference. Mine wouldnt hardly get above 3000rpm and it was causing the trans to shift funky. Went with a Magnaflow high flow cat and now all is good.

 

Im sorry you're not getting better responses. I've been busy and not paying enough attention. Obviously it's not your cat since you don't have one. Beware jumping on the ECM bandwagon that's expensive and not likely the cause of your problem. Try unplugging the O2 sensor. This will keep the system in open loop and eliminate a possible faulty O2 sensor causing the ECM to remove fuel. Suspect a shot distributor. You can test the pick up coil(beneath the rotor) with an ohmmeter. Should read 800-1000 ohms. If the "teeth" of the pole peice and/or timing core are loose or damaged in any way, replace the dist.

 

ASE Doc, it just nice that you take the time to read and reply, no hurry. I have rebuilt the dist, new module and pickup and it needed it - green inside until i shined it back up and replaced everything, but no difference. I finally checked the codes in the computer even tho no SES light was on and it gave me the code 22 which is low voltage from the TPS. I checked the TPS and it was reading right with a digital multimeter, but I bought a new one today in case it was acting erratic and it is. Every now and then it will run pretty good, but most of the time i can hold it at half thottle and it will start to rev up, then kinda just hang there not going up or down. Let up on the thottle and it will pick up. Believe me, I appreciate you and everyone else that is on here to help a poor guy out and time isn't an issue. That code 22 sure pointed to the TPS even tho when I checked it (when it was cold tho) it was varying between .55 at closed thottle and 4.93 at WOT. If that doesn't do it, it was throwing a code 42 also, but the timing connector is connected. Made sure after I timed it after the dist overhaul. Maybe me bringing those points up will help someone help me. Thank you to all that have chimed in. I appreciate all of you!!!! :-)

 

The code 42 is normal after running with the timing connector undone to set timing. Be sure to clear this code as it puts EST system in bypass mode. Short of restricted exhaust or intake, the only thing I can think of that would cause the engine to simply not rev is lack of fuel. Without fuel the engine will fall on its face, even with no load. Retarded timing will cause lack of power but the engine will still accelerate, though slowly, as long as it has fuel. The TPS affects asincronous injector pulses, and decel fuel cutoff, compensating for sudden throttle changes. It's possible that the TPS would cause the no rev, but I don't really see it. Dumb question, have you looked at the air filters?

Also, a common cause of intermittents is wiring faults, which could also explain the code 22. Check all of the engine grounds, including the body grounds by the battery and those at the rear of the heads. A very handy tool for chasing intermittents is a scan tool to watch engine data. This lets you see sensor voltages as the ECM see them.

 

wish i had a scan tool or a place to "loan a tool" from. Brand spankin new air filters, so I'm trying my da*&%#%$ to figure this silly little problem out. Will check those grounds, as my work in electronics has always showed to check them first, usually that is the problem. I will trudge away. As always, thanks!!! :-)

 

Well ASC doc, checkin in with you. I replaced the TPS and adjusted it, still no change BUT..... when I UNHOOK the MAF sensor, the problem pretty much goes away. What do you think, need a new MAF? I tried cleaning it and when I did it didn't make any difference, but I noticed that the "seal" around the bottom of the unit was coming out almost as if a bakfire had blown it out in a couple areas. When you get a chance, give me some more of your opinion, which I trust. Thank you. :-)

 

Yeah, I was thinking MAF from the start. As I said before, unplugging the MAF places the ECM in default or limp in mode where it runs on a default fuel map, ignoring the MAF sensor. When a car straightens up with the MAF unplugged, it means that the MAF is the problem. I would replace both the power and burn off relays with the sensor just to be safe.

 

Thank you to ASE doc and all the others for the help in getting "Sweet" running like she used to!!! Running so smooth now that I can't remember when it did run like it is. Feel free to use this as a example with any others that are experiencing the same or similar symptoms. Sincerely, Topless87.