Hesitation, please point me in a direction - Team Camaro Tech
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post #1 of 31 (permalink) Old Nov 1st, 02, 01:29 PM Thread Starter
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Hey everyone need some advice. Im still working the bugs out of this Z28. 85 305 TPI
So I idle good about 6 to 700. If I romp on it I have a little hesitation but not much. However during normal acceleration I have very bad hesitation on and off. Some days better then others. Very few days not at all. I dont have any codes. Even had a buddy put his scanner on it and nothing. A local shop didnt find any either. I have good vacuum at about 18 - 20 New coil and rotor, plugs and wires and pretty much all my sensors. Everything is pretty much new or rebuilt. I dont think im running rich or lean. I have been leaning towards fuel problem or a bad plug or wire, but at this point im just guessing. I just bought a fuel filter but didnt put it on yet. I dont have a fuel pressure gauge, but when I did check it after the rebuild it was 42 psi. I dont know if this has anything to do with anything but last week I noticed my fuel cap leaking fuel down the side of the car. I replaced the cap and would say the car ran 50% better. Please point me in a direction to look. Thanks as always

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post #2 of 31 (permalink) Old Nov 2nd, 02, 04:56 AM
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Try the new fuel filter first. If the problem persists you might want to check your throttle position sensor. They can sometimes develop a dead spot that the on board diagnostics won't pick up.

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post #3 of 31 (permalink) Old Nov 2nd, 02, 07:21 AM Thread Starter
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Im going to change the filter today, but the TPS is only a month old. Thanks for the ideas.

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post #4 of 31 (permalink) Old Nov 2nd, 02, 07:39 AM
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Look for vacuum leaks. Are the sealing tips or o-rings properly installed on the fuel injectors? Try waving propane from a torch around (unlit) gasket areas and the fuel injectors - see if RPMs change. Some folks use WD-40. A vacuum leak is a high probability.

Put an ohm meter accross the terminals of your throttle position sensor and see if the resistance changes smoothly as you slowly open the throttle by hand.

Check your fuel pressure again, but this time pull a vacuum on the fuel pressure regulator (near the end of the fuel log) and see how pressure changes with vacuum. It should decrease with vacuum and supply adequate pressure with zero vacuum.

Is idle speed OK? Does it idle fast when cold started but idle down on it's own after a couple minutes (depending on the temperature)? If not, the the idle air control motor may be sticky, but that shouldn't affect hesitation.

Consult a service manual for how to check the manifold absolute pressure sensor (MAP). The procedure probably consists of back-probing the connector and measuring DC voltage accross two of the pins looking for a specific voltage change. If you have a mass air flow sensor (MAF), check the procedure on checking it, which should be similar to the MAP procedure.

Does the check engine light come on for a few seconds prior to cranking the motor over? It should as a lamp-test. If not, then you may really have a code, but can't see the light flash.

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post #5 of 31 (permalink) Old Nov 2nd, 02, 09:17 AM Thread Starter
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I used carb cleaner on every vacuum point I could find A while back and my plenum was leaking. I fixed the Plenum and I sprayed it all over again and didnt hear anything. Does propane work better? Or was the carb cleaner ok?

Idle speed is good. Start up is about 1200 then a minute later drops to 6 or 700. My timing is set about 10 before.

I had a MAF code about a month ago. I replaced it and the car ran ok for a few weeks. The problem I was having before was a total lose in power when I romped it. It would take off like a jet then all rpm's would drop like someone turned off the fuel then back on again. Like I said I replaced it and it was fine. Now it just hesitates during normal acceleration. Some days not at all but most at least some. Some days better then others

I need to get a new voltmeter and vacuum gauge to check the rest of the stuff you were talking about. My X wife ran them over. Long story.. Thanks

85iroc
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post #6 of 31 (permalink) Old Nov 2nd, 02, 04:01 PM
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There are two theories on checking for vacuum leaks with sprays or propane. One is that the stuff actually burns and changes RPMs. The other is that spray liquids will temporarily plug the leak causing RPMs to change. I like propane because it doesn't make a mess. Also, with carb cleaner you have to be careful. That stuff will damage rubber parts which can be particularly bad with fuel injected engines. Fuel injected engines are full of o-rings (around injectors etc.) and sensors with rubber parts. WD-40 would be a safer alternative.

-dnult
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post #7 of 31 (permalink) Old Nov 3rd, 02, 11:56 AM
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85 Iroc,
Did you set your timimg with the EST wire disconnected? Tan wire with black tracer. Location should be noted on the emmissions label under the hood, it's a single wire connector. Timing should be set with this unplugged, then plug back in and disconnect battery cable to clear code once finished.

Another cause I've seen is a bad EGR valve.
If it's an electronic one (wires w/connector) they will set a check engine light when they screw up. If it's vacuum operated it could be sluggish and/or carbon build up on the pintle seat. I don't think they were using electronic EGR's back in 85'.

You may also want to look at the PROM in your ECM. There is a small cover on the ECM with two 1/4" screws holding it. Take the cover off and you will see the PROM and it will have a 4 digit alpha code (like AFXA) write that down and go to a dealership and see if that is the newest PROM available. It's called a "calibration" and has all the timing and fuel curves built into it. GM made many changes after cars were out on the street to correct problems like the one your having. I put one in my 95' Blazer over a year ago and GM had made 5 calibration changes at that point. It was like giving the truck a tune-up, it ran much better.

Hope this helps, Drew
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post #8 of 31 (permalink) Old Nov 4th, 02, 12:34 AM Thread Starter
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Hey drew,

Thanks for the reply. No I didnt set it with the EST wire disconnected. Im not even sure what that wire is. I have an aftermarket hood, and no emissions label anywhere.

When I bought the car it had a hypertech chip in it and I didnt know it. I went out and got a hypertech chip for it went to put it in. This is when I found out I had one. So I dont have an original chip anymore. Im in the process of getting one now. Im not at all happy with the hypertech. Anyway to the point A few weeks after the rebuild I had all those sensor problems. My MAF and MAT kept coming up and the last drive I made I also got a EGR code. I replaced the chip with the other one, reset the ECM and all the codes went away. It ran fine for a few weeks then the hesitation started.

Do you think going back to a stock chip will help? Or do the timing with the EST off? Or new ERG?

Thanks Drew

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post #9 of 31 (permalink) Old Nov 4th, 02, 12:50 AM
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Good morning, 85 Iroc.

I would take up on Drew's suggestion and get an OE chip for it. Be sure to take the VIN with you, if not the car also.

The EST wire should be either pass side firewall in the engine harness, or under the heater in the floorboard of the pass compartment.

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post #10 of 31 (permalink) Old Nov 4th, 02, 01:01 AM Thread Starter
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Good morning all,

In not sure what you guys are talking about when you say EST. Are you guys talking about the Electronic Spark Control?

Thanks

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post #11 of 31 (permalink) Old Nov 4th, 02, 01:26 AM
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Hello 85iroc,
No, it stands for Electronic Spark Timing. It is located on the passenger side firewall near the air conditioner unit. It is a single tan and white or black wire with a connector. The electronic spark control is mounted on the drivers side firewall and has about seven wires going into it. If I remember correctly, it was depicted in one of the diagrams that I sent to you. I also believe that this was one of the questions that was asked of you on some of your previous posts.

Good luck!!

The Trickster!!!!!!!!!!!!!!!!!!!!!!

[This message has been edited by trickster (edited 11-04-2002).]
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post #12 of 31 (permalink) Old Nov 4th, 02, 04:36 AM Thread Starter
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Thanks everyone, let me give all this a try in the next couple days. I let everyone know what happens.

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post #13 of 31 (permalink) Old Nov 4th, 02, 07:20 AM
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If you have the HEI distributor with the big cap with the coil mounted on top you probably won't find the tan wire with a black stripe. Most of these have a four wire connector on the opposite side of the cap connector. With the ignition off disconnect the four wire plug. This will zero the timing. Now you can start the car and set the timing. Most hypo chips require setting the timing at 0*. After you set the timing, shut the car off and reconnect the four wire plug.

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post #14 of 31 (permalink) Old Nov 4th, 02, 11:39 AM
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Hey 85 Iroc,
I would go back to the newest (latest) GM prom for your car. I haven't seen very good results with the hypertech proms. Others may feel differently and may have had some good results, I for one opinion haven't. Cost for a new GM prom should be around $40-$45 dollars. I do however vote for the hypertech programmer for a PCM. I set a car up with one of those and there are all kinds of options you can dial in. Best $300 bucks you could spend on higher performance.

Trickster sounds like he knows where the timing connector is. It's one wire that is tan with a black or white tracer on it. I think GM has used both.

I wouldn't mess with the EGR yet until, 1st set the timing up right, 2nd change the prom. The EGR valve will be the most expensive option and no sense in spending more money if the first two will get you where you want to be.

Chow, Drew
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post #15 of 31 (permalink) Old Nov 4th, 02, 12:37 PM Thread Starter
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Well I definitely have a direction now. The problem I have now is that PEP BOYS still has my car. 7 days now. I brought it in to replace my front main seal and rear pinion seal/yoke. I got the car back Saturday with a horrible scraping noise in front of the engine. They all just looked at each other and said idunoo. They crushed the timing chain cover and the chain was rubbing. No radiator hoses were tightened down. Antifreeze everywhere. Two vacuum lines broken off. Power steering fluid all over a freshly shinned and painted engine. They forgot to put the cap back on. And I had my windshield wiper vacuum hooked up to my Emissions can. The correct one was sitting right next to it hissing. They did a wonderful job. So they tore it back down to replace and fix everything and broke a tool off in my crank. So needless to say I donít have the car back yet and I wont be going to PEP BOYS again. So if I ever get it back I can do all the stuff you all suggested. Sorry for the story I was venting. But I did order a new PROM and get rid of hypertech. I have had nothing but problems. Also 1 2run said put the timing at 0*? If I put it at 0* my car wont run. Or did I misunderstand you? It is set right now at 10 before, and idles at 700. Please bare with me guys this was my first rebuild, and I was happy just to make it run.

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