first to start i know i should have a sig so everyone knows what kind of vechile im talking about but ill give all the info i have right now.

its a 87 iroc-z28 and is supposed to have the 5.0 tpi as per vin tag

as far as i know (from block numbers) the engine is a 350 out of a 67-72 truck or a 327 out of a 67 camaro? the heads are def 350 heads and it has modern tpi intake setup. i had gotten the car from a gentleman that said original engine caught fire and he installed this engine but could not remember what the engine came out of.

now for the problem, dosent do it every ign cycle, but every 4th or 5th cycle, or even every other cycle, or if sitting idling for 5-10 minutes, the car will act fine untill i get maybe 10 feet down the road then it acts like its not getting fuel, hesitates, pops threw intake and has a bad odor of burning stale fuel, at light throttle its ok and at full throttle its ok, just anywhere in between it has all of these symptoms. every time this happens engine light comes on and same 2 codes?

i have replaced tps, maf sensor, ecm, and even cleaned the throttle body, plentium, and intake runners. replaced all vacumn lines i could find, performed flow chart diagnosis from snap-on's shop-key(mitchell on demand) and all test came back fine. this is far from the first vehicle i have worked on and picked up the car as a project and always wanted an iroc. i'm at a lost and even have had other mechanics look at it (that are freinds, never paid a shop). sorry for the long rant, just trying to give all the info i can. is it possable that its because of tpi setup on an older 350?
any help is appericated and feel free to ask any questions or give any comments.

thanks in advance
bill

 

Simple things first ... Most problems come from the dumbest little things ...

All plug wires good? Even new ones are bad out of the box.

All wires 'snapped' securely on the plugs? I had one that would 'pop' itself off just enough to cause an issue one time, drove me nuts until I figured it out.

When was fuel filter last replaced? That's a cheap 20 minute job that can make all the difference in the world sometimes.

What's the fuel pressure? There's a schraeder valve driver side fuel rail (like a tire valve stem) - you can 'rent' a pressure guage at Advance/AZ for free and check it.

What's the base timing set at? Remember you have to disconnect the EST wire before startup to check base timing, and reconnect after adjustments (if any) are made and car shut off.

Ever change out the ignition module in the distributor? They are elctronic, and have a plate that gets greased with dielectric grease during install - over time the grease dissipates, the plate rusts, causes resistance, and the heat build up kills the ignition module. About $35 for one - make sure it comes with the grease and use according to directions.

Gives you some simple cheap things to look at anyway.

 

Ooops. Got to reading the post, forgot all about the codes

Maybe none of that will help with those codes - sorry - got on a roll and forgot

 

sorry forgot code definitions so you dont have to look them up

21- throttle position sensor error (signal high)
33- MAP sensor circuit error (signal high indicating low vacumn)

and thanks for the info, and already tried all of that, first thing i do when i buy a car is give it a full tune up, even if seller says it was just done (piece of mind i guess). i know its probally something stupid, ive just been over everything so much could be overlooking something small. car was origanlly a project but because of my wife giving up a lease and not wanting another car payment it turned into a daily driver.

also noticed it does it more often as the weather warms up, when its below freezing it barley ever happens, as it gets warmer out happens a lot more often.

thanks again
bill

 

Well - I'm out of the loop then, 'cause I'm certainly no TPI expert! I'm sure others will post up with some better TPI specific thoughts. Good Luck!

 

thanks, i hope someone else does cause im no tpi expert either, i think i might be better off putting a carb on and call it a day.

 

If this car has the TPI electronics from 87, it has a MAF sensor, not MAP. The 33 code goes for either. If this were a speed density system with these two recurring codes, I would look for a fault in the ECM ground circuit shared by the TPS and MAP sensors. Since your car is most likely a MAF system, this doesn't apply since the MAF and TPS don't share a ground. The MAF code 33 is for high airflow, meaning that the MAF indicated higher airflow than was expected by the ECM under a given set of operating conditions.

What comes to mind, given the relationship of the symptoms to throttle position is a faulty TPS. Check the TPS using an analog voltmeter or better yet a lab scope. It should show a steady rise from .5 to 4.5 volts as the throttle is moved from closed to wide open. Look for drop outs or glitches. Check TPS ground circuit. Check MAF sensor ground circuit. Wiggle test while the car is running and watch for changes.

BTW, you'll want to perform this test when the problem is occuring, the bummer with intermittents. If no trouble is found with the TPS, go back to the trouble tree for each code and proceed through them, as the problem is occuring. You may find that the problem is internal to the ECM. This fits with the relationship to temperature. Check all ECM grounds carefully.

 

ok thank you ASE doc ill give that a shot, wouldnt be the first time i got a faulty sensor new.

 

Yeah, and there is correlation with throttle position when the failure exhibits itself. However, there is also correlation with tempurature. The more I think about it, the more I think of wiring glitches. I don't know if there is a data recorder available for the ODBI GMs(12 pin ALDL). Rbob might know of one. You can find him on the DYI Prom forum. If there is one, you could use it to record data over time and perhaps catch changes in sensor data as the problem comes on. This may tell you where to look. Sensor voltage shifting high(above 4.5) generally means a loss of sensor ground.

If this car were at my shop, I would be attacking the ECM harness with my lab scope attached to ECM power and sensor ground, looking for glitches. I would warm up the car trying my best to recreate the failure, while watching data on a scan tool. Intermittents suck because they're intermittent. Half the battle is getting the trouble to show itself while we're watching. This can eat alot of time. Using data recorders and diagnostic setups can help by keeping us ready when the trouble pops up.

Throwing parts at the problem is a common mistake and can get real expensive. If the problem is in the wiring, all the parts in the world will never fix it. Also, as you just mentioned, installing a bad part can make things even more fun since we tend to want to trust new parts. Going back and rediagnosing these parts can be painful. Good luck and please keep us posted.

 

thanks again ASE doc, i think i have it figured out, looking at it last night i saw that the harness to tps was bent and kinked, i wiggled around the wires and idle was going up and down, going out after work to pick up new harness connector for tps, luckly the bend/kink is about 3 inches from connector, its just amazing how far you get into something and dont realize the simple thing staring you in the face. wouldnt have even looked for it if you didnt mention a "wiggle" test, hopefully this solves the problem, ill keep everyone posted on what happens.

thanks again
bill