I'm new to this board and I'd like to start out by saying hello, and I also could use help with my camaro hesitation problems.

I did a search on the board for hesitation and I got many results, so I know this has been gone over many of times.
I was hoping someone who has had the same exact problems and had them fixed could inlighten me a bit.

I have a 88 IROC 350 tpi with a 700r4.
It also has a, gutted air filter box, throttle body foil, 160 deg stat, and large capacity trans pan.
I had a rebuit engine put in @ around 97,000mi

It ran OK after the rebuilt engine was put in despite the temp guage not working and the car seems as if it has lost some power compared to the original engine.

Everthing has been ok after engine swap, about 10,000+ , then a few months back I get, off the line(low speed) hesitation problems, like the gas line was being pinched. The problems have persisted and got worse. I brought it to a small town mechanic my buddie had been goin to, he said it had a code 33 I went out a got a rebuit MAF and Installed it, code 34?, didn't help. I figured I try another rebuit one just incase the first had a problem,nope.
The mechanic said he could go no further without having the code problem resolved. he aslo said it could be a ECM problem.
So I bought a used rebuilt ECM, then I reinstalled my old MAF because I don't think it was bad, hooked up the used ECM myself, then cleared the codes. Now I'm not getting any codes anymore but still have the hesitation problem. You give the car some throttle and it's like you were cutting off the gas supply. It's weird though if your able to get the rpms up full throttle it seems to be fine, except when it reaches 5,000rpms then it gets fluttery(slight popping sound, not detination)
I just replaced the fuel filter and pressure checked the fuel rail. It read under 10 during prime, 25-30 at idle and 25-30 @3,000prm
I get the normal 2 second fuel pump hum. I don't hear any whine from the rear.

I don't want to go back to the small town auto shack and get bent over again for diagnostic fees.

I'm not familiar with all of the electrical part terms so please elaborate in your replies.

Please help ASAP,

I think I'm going to bring the car into a different shop tomorrow, I was hoping I could give the mechanic some ideas, insted of him giving me it could be this and could be that, and I'll end up being charged for work that isn't necessary.

Thank you,
Sorry I didn't mean to write a book here.

conbrio....

 

Fuel pressure is too low. It should be around 35 at idle with vacuum hooked up to the pressure regulator, around 44 with vacuum disconnected.

Fuel pump? or possibly the regulator

 

What is the fuel pressure with the vacuum line disconnected, the pressure should go up with less vacuum and max out with no vacuum. Have checked any plugs to see what they look like, checked for vacuum leaks. Did it get new ignition parts with the new engine?

Nick

 

No Code 36 (Maf sensor burn-off circuit)? My friend's '88 Iroc 5.7
had a bad burn-off relay and it ran poorly. His '91 was also running funny and he changed the fuel pump. He sail his pressure was about 42 after the new pump install.

 

I'd say pull all your plug wires and check the condition of them.

 

Conbrio,

Welcome Aboard!

It's generally better to include as much detail as you can, since most of it can be very relevant and helpful. Its always better to include everything.

There may be no need to visit a mechanic just yet. With a few basic tools you can get a lot of information, and either solve the problem yourself or have some very specific data for the mechanic, probably saving some diagnostic time and $$$.

You've already been given some reasonable advice based on what you posted. The ignition wires may solve your higher RPM misfire, but that may not take care of the hesitation. There are a few things that are necessary for good accelleration:

1. Strong spark;

2. Adequate fuel delivery (thus the fuel pressure questions);

3. Correct ignition timing;

4. Good compression;

5. And a correct Throttle Position Sensor (TPS) adjustment.


The TPS adjustment is relatively easy to check and set. All you'll need is a digital voltmeter and a small Torx driver. The digital volt meter (DVM) can be purchased almost anywhere for around $20.00. You don't need a top-quality instrument for the relative checks you might be doing to start with, but increased accuracy is always better. If you don't want to spend $250.00 on a higher-end meter, the $20.00 variety will get you close enough to start with. Think of is as a half-hour of diagnostic time charges in the shop - and you can use the meter for a lot of other things, too.

The fuel pressure can be tested with a gauge that connects to the fuel delivery rails. If you don't have one, you may be able to borrow one or spend the $30.00 on a low-priced unit. Again, the entry-level gauge is probably fine for what you will be doing.

With the data from the fuel pressure checks and the TPS voltage setting, you will have some good information to start the diagnosis. The fuel pressure test takes a whole two minutes once you have the gauge, and the TPS voltage check may take five-ten minutes for the first-timer.

Again, Welcome. I think you'll find a lot of helpful information here, and certainly no shortage of opinions. We can probably walk you through the diagnostics pretty easily, and get you running again. There are countless ASE certified technicians, highly skilled builders, expert programmers, tuners, and experienced enthusiasts among our membership. Now you're one of us.

 

Thanks everyone for the fast replys, welcomes and help.

I checked the fuel pressure with the vacuum lines connected.
I didn't get any new ignition parts with the replacement engine besides plugs. I had a tune up prior to the replacement engine, I think the wires, cap and rotor are all ok.

Vader, or should I call you lord Vader?

Could you give me a little more info on testing the TPS?
I think I can-hopefully learn/figure out a MMeter.

If anyone else has anything to add, it will be much appreciated.

Thanks again everyone,
conbrio

 

In case you haven't noticed yet, Vader is Gawd :hail:

Add one more vote towards the fuel pump or regulator.

 

Your fuel pressure is a little on the low side. The factory specification for a TPI engine is 37 PSIG +/- 3 PSIG at idle with the vacuum connected. The new fuel filter eliminates that possibility, so the next thing to test is the regulator. If you pinch the fuel return line shut with some smooth-jaw pliers (or between two soft pieces of wood in the pliers) you should be able to get the fuel pressure to well over 50 PSIG. If the pump is good, the pressure should rise. This would indicate a failing regulator. If the pressure doesn't rise, you may have a weak pump and the only solution could be replacement.


At 10,000 miles, the ignition shoudl still be good, but it has enough mileage and enough symptoms of poor spark that it would be a good idea to check out everything. If the cap and rotor look good, just reinstall them. You can test the ignition wires and coil with your new meter. Let me know when you're ready and we'll get you the specifics. The plugs are an easy call. For a buck apiece, if they even look suspect, dump them and install new ones. Nothing fancy, just plain old copper-cored AC/Delco and Champions correctly gapped.


A digital meter is pretty easy to interpret. As for the procedure, you asked for it:

Throttle Minimum Air Position

Tools needed:
1. Torx driver # T-20
2. Paper Clip
3. Small Punch
4. Tachometer

GENERAL NOTE: The engine should be at normal operating temperature before performing any adjustments. Never rely on the dash mounted instruments for diagnostics and adjustments. The oil pressure and temperature gauges and the voltmeter and tachometer just aren't calibrated accurately enough for diagnosis, but are a relative indication for monitoring the vehicle while driving.

For this adjustment, the transmission will be in DRIVE while you're under the hood. You will need to securely set the parking brake and block the drive wheels. It would also be a good idea to have an assistant hold the service brakes while you perform the adjustments.

In order to successfully complete the adjustment, the IAC air passages and pintle need to be clean. The throttle plates and bores need to be clean as well. If this is not the case, you'll need to remove the air cleaner from TBI engines or the intake air bellows from TPI engines to gain access to the area to be cleaned. A spray-type carburetor cleaner works well for this. Cleaning the IAC passages on a TPI/MAF engine will set a DTC, but we'll be clearing that later. With the engine idling, direct the spray cleaner into the IAC air passages and around the throttle plates. Shut off the engine and continue cleaning the throttle plates by opening the throttle manually. Once everything is satisfactorily cleaned, replace the air bellows on TPI engines. Many times, this alone can solve IAC/idle speed problems.

If this doesn't solve the problem, you may need to remove and clean the IAC stepper motor. If the IAC appears to be clean and functioning properly, continue with the adjustment procedure.

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Idle Air Control Cleaning

You can remove the IAC and service it. Remove the electrical connector from the IAC. Unscrew the IAC unit from the throttle body.

You can gently rock the pintle back and forth and allow the spring to extend it until it comes apart in your hands. Clean everything with lint-free cloths and a mild solvent. Harsh solvents can affect the insulation of the stepper motor coils. It's generally the dirt and buildup on this worm shaft that causes sluggish IAC operation.

When the worm gear on the pintle shaft is clean and dry, apply one drop of clean light oil to the shaft and work the pintle back into the rack gears of the motor by the same rocking motion. It takes a while to get the pintle back into the worm gears, but you'll get it. It is important to get the pintle fully retracted into the housing so that the pintle is not forced against the gears when reinstalling the IAC unit in the throttle body.

While the IAC is out, clean the air passages in the throttle body. The oriface in the TB where the IAC resides is the seat that the IAC valve closes against, and it can accumulate a lot of carbon, dirt, and debris. The easy way to do this is with carburetor cleaner and a small stiff brush.

When everything is clean and dry, replace the gasket if it is damaged, apply a little anti-seize to the threads, and torque the IAC to the proper specs. (13 ft/lb for '85-'89 , 30 in/lb for 1990-on.) Proceed with setting the TPS and minimum air position.

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Locate the Assembly Line Diagnostic Link connector under your dash panel. Remove the cover if it is still there.




Cut and form a paper clip into a "U" shape. Insert the clip ends into the ALDL in the 'A' and 'B' sockets.




Turn on the ignition, but DON'T start the engine. This will force the ECM into its diagnostic mode. Wait 30 seconds to allow the IAC pintle to fully extend. With the ignition still on, go under the hood, remove the electrical connector from the IAC, then turn off the ignition and remove the paper clip jumper from the ALDL. With the IAC pintle fully extended (closed) all idle air will be controlled by the position of the throttle plates. Some manuals indicate that the EST bypass connector should be disconnected for this procedure, while some make no mention of it. While timing is a factor in idle speed, the EST should only operate as a function of engine RPM, temperature, and detonation sensor inputs. To remove all doubt, disconnect the EST bypass connector is your car is so equipped. Some TBI and V-6 engines do not have this bypass connector, and therefore must be set with no regard to the EST system. The EST can be bypassed on some cars by grounding the diagnostic terminal at the ALDL and continuing with the procedure, but the fuel mixture will be skewed to the rich side, affecting idle speed as well. In any event, the minimum air position idle speed range is wide enough to allow for some variations. As always, it is best to consult your service manual for the exact procedure for your system.

Locate the Torx screw on the left side of the throttle body. It may be equipped with a protective metal cap from the factory. This was intended to discourage adjustment. If the cap is present, use a small punch to knock it out. Once the screw is accessible, start the engine and place the transmission in DRIVE. Adjust the throttle stop to obtain 400-450 RPM with the transmission in "DRIVE" on an automatic transmission car, 450-550 in neutral on a manual transmission car, rotating the Torx screw clockwise to raise speed and counter-clockwise to lower speed. Once the idle RPM is set, place the transmission in PARK and turn off the engine.

Re-connect the electrical connector onto the IAC. Start engine. Idle speed should be governed by the ECM at approximately 600-650 rpm in "DRIVE" (for unmodified cars). Idle speed in NEUTRAL or PARK is less significant, and will be higher.



Throttle Position Sensor (TPS)

Tools needed:
1. Digital Volt-Ohm-Meter (VOM)
2. Breakout jumper wires or probes (make your own)
3. AutoXray, Diacom, or similar scanner will replace the VOM and jumper wires.

Turn on ignition, but don't start the engine.

With a diagnostic scanner: plug in the scanner and read the TPS voltage. It should be 0.54Volts +/- 0.07 VDC.

Connect the VOM to the TPS electrical connector terminals ‘A' and ‘B'.

With a breakout jumper: Disconnect the electrical connector from the TPS. Install the breakout in-line, between the TPS and wiring harness connector. Connect the meter probes to terminals 'A' and 'B' on the connector. (‘B' is the positive connection, ‘A' the signal ground, or negative.)

With probes: If you have very slender probes on your VOM, you can back-probe the TPS connector while it is attached to the TPS. If you have made probes of large dressmakers pins or a similar item, you can back-probe the connector as well. Connect the meter probes to terminals 'A' and 'B' on the connector.

Turn on the ignition to read the TPS output voltage at the idle position. The reading should be 0.54VDC +/- 0.07VDC. The ideal is the center of the range, 0.54VDC for a stock engine. To adjust the output voltage, loosen the two Torx screws holding the TPS to the throttle body, and slightly rotate the TPS up or down, reading the voltage until it comes into specification. Tighten screws. Using the throttle lever, rotate the throttle to WOT (wide open throttle). The TPS voltage should be over 4.0 volts. Close the throttle again, and then slowly open it to WOT, observing the voltage reading. It should increase progressively and in a linear fashion. If it sticks or jumps or falls off at all while doing this check, the TPS sensor may be failing and could be a cause of stumbling and driveability problems.

After achieving the desired setting, turn off the ignition switch. Remove all jumpers or the scanner and reconnect the TPS connector as required.


Reinitializing the ECM

If you set a DTC during the procedure, the SES light should be illuminated on the dash. This ECM retains DTC data for the previous 50 engine starts, so the codes will eventually be cleared. If you want more immediate results, after shutting down the engine disconnect the negative battery terminal for five minutes. This will clear the ECM of all diagnostic trouble codes. Clearing the ECM also clears any data learned about your engine, and clears the radio presets. If you have a Delco-Loc or Theft Loc II radio, make sure you follow the procedure to unlock the radio protection before disconnecting the battery. This five minutes is also just about long enough to clean both battery cables. Reconnect the battery. When you first start the engine after clearing the ECM, the engine will operate with base parameters programmed into the ECM PROM. These parameters may not be optimum for your engine, but the ECM will enter a Block Learn Mode soon after the engine is warm and enters Closed Loop Mode. The ECM will write new data tables specific to your engine and will eventually rely on those tables instead of the base tables of the factory program. You can expedite this process by driving the car for 20 minutes under varying conditions to allow the ECM to initialize. Or you can wait and drive the car normally at your convenience. The BLM tables are constantly being updated as sensor input ranges change, but the greatest change will occur within the first twenty minutes of Closed Loop operation.

 

I appreciate everyones help.

I got my car back from being diagnosed again.
The mechanic said I needed a fuel pump, BG fuel/air induction cleaning, and tune up, $1,700.

I don't have that much $

Vader, I tested the fuel pressure again with the car running and pinched the return line, No change.

Did I preform the test properly? in my 86 shop manual it says to apply battery voltage to pump test terminal, pinch return line and pressure should be over 60.

(Apply battery voltage to pump test terminal) How do I do that?

If I do get a new fuel pump can I use a Holley hi-flow 255lph in tank pump? overkill?

Thanks,
conbrio

 

Conbrio,

It sounds like you performed the test correctly. If you're certain the line was pinched completely closed, and the pump was energized by either running the engine or jumping power to the pump, it should have developed at least 50 PSIG. Even with an injector stuck open at 100% flow, the pump should maintain 50 pounds at a minimum.

A high flow pump is overkill unless you are going to use that much flow due to heavy modifications. If you don't use the flow the pump will work that much harder to deliver the "normal" amount of fuel, and the rest of the pumping enrgy will be wasted in keeping the FPR relief valve open.

If you aren't going to perform the work yourself, get the pump and filter replaced at least. You can do the rest later.

And even though you already replaced the fuel filter, if you suspect that the tank was run out of fuel or was somehow contaminated, you may want to try another filter just in case. You should install a new one with the pump anyway, so gettng an extra AC filter wouldn't hurt.

 

Vader,

Just to triple check, how do I jumper the fuel pump @ the ALDL?

I asked holley direct today if the Hi flow was ok to use with a no mod engine, They said "it will be fine" . I just wanted to make sure.

Thanks.
conbrio

 

You know what? I had the exact same problem with my car. Vader, I do not want to trash anything you say, cause you know all:hail:
but the problem is not the fuel pump. If the car runs still, then the pump is ok. And it's not the filter, that I believe was decided earlier. What I found to be the problem ( i posted a fuel pressure topic about a week or two ago), that to me seems to be overlooked, was the fuel pump strainer. The old one had kind of collapsed on itself on one side, and those things are supposed to flow for that fuel pump. Let me tell you, once i put the new one in, and got my car back together, my car never started and ran so well before. All it takes (i'm saying this like it's quick and simple

is 4-6 hours of labor and $5 for a new high performance strainer from good o'l NAPA.
'Course, I could be wrong, but thats what was wrong with my car. Oh, I also did all those sensor checks and stuff, so I managed to rule that one out, and if you do drop the tank by yourself, make sure the pump is on the in-line tightly, cause mine was a little loose.

 

No arguments there. That's why I asked about whether the tank had been run empty. That's a good way to clog the "sock".

After having removed the tank, you should know as well as anyone how much work is involved. Regardless of whether the pump has failed or the sock is plugged, the tank and pump assembly has to come out. I am just trying to get Conbrio to verify the fuel pressure test before he unnecessarily removes the tank - it would be a lot of wasted effort if it weren't needed. I understand what you're saying.

I had a similar problem once, and even though I found the problem was NOT the pump, I installed a new one anyway, since I didn't want to have to drop the tank again in another year or two. Cheap insurance, I guess.

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Conbrio,

Of course Holley is going to say their pump will work just fine - what else would you expect then to say? Call back and ask it they can guarantee that their pump will last ten years like the original AC/Delco pump.

As for the pump power at the ALDL, connect a wire to a 12VDC+ source, like at the fuse panel or cigarette lighter. Connect the other end of the wire to the 'G' terminal on the ALDL connector to energize the pump. This should be done when the engine is OFF.

And don't forget to try one more filter if the fuel tank has been run dry.

 

I'd like to thank everyone for there help and input.
I got my car back today after being serviced (holley hi flow fuel pump @$150 and labor @$400) It seems to run like new now!!!


Again I appreciate everyone's help,
conbrio