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Old 01-26-2005, 11:02 PM
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Need FI help. I am stumped so far!

My TPI problems seem to persist. Its an 86 TPI on a 66 gmc. No emissions stuff, no a/c, th-350 trans.

I have cleaned the IAC and throttle body. Reset the idle based on factory procedure. The TPS is set at .54. Timing is at 6. No vacuum leaks that I can detect. At 825 RPM I am pulling about 15 inches of vacuum. Thats where it was before I started having these problems as well.

The problems snuck up on me. I had finished putting on new heads, and had it running very nicely for about 3 weeks and then it started acting up. At first, it would idle nicely, but if you didn't press the throttle slowly, it would pop (sometimes) and cutout like it had suddenly died but then catch itself and run. If you slowly got on the throttle, there would be no problems.

Now, it idles erratically. Not all the time however. Sometimes, in park it will idle nicely (however at a higher idle, 800+ rpm). When I put it in gear, most of the time the idle drops low enough, quick enough that it dies. In drive it idles at 575-600 RPM. At times, this bounces between 400-625 RPM. When it begins to bounce, it almost does so rythmically. Revs, dies down, revs up, dies down. Its about a three second cycle between up and down. If I give it any amount of gas, it holds its RPM's fine. At times, the idle also bounces in park, though not as much, and not as wildly.

I let it idle for about 12 minutes and warm up to operating temperature. It never went into closed loop that my scanner saw. The injector pulse width would vary between 1.7 and 2.1 in park, and in drive, idling, between 2.2 and 4.

I have tried another MAF and it was the same. Could this possibly be a computer fault that is not throwing a code? I've worked with this TPI a lot but this one has my kind of stumped.

Let me know if any other sensor info that might be helpful in fixing this problem. I will list what I have on my mind below.

At idle in park at 825 RPM

MAF Grams per second - 9.
Pulsewidth - 1.7-2.1
Coolant temp - 180
Intake air temp - 63 (its about 40 outside right now)
Oxy Mvolts - 447
Oxy cross count - 2
Rich/lean - lean
Open loop.
IAC steps -145

Let me know if you need anything else lol. I hope someone has an answer. I miss driving it, and at the same time its driving ME nuts lol.

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Old 01-26-2005, 11:10 PM
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Any Chance the oxygen sensor is damaged. My camaro did the same thing right after I had the alignment done on my car.

Why because the oxygen sensor hit on the ramps going on to the alignment bench. It was cracked with the wire still on it and everything so it didn't look like anything was wrong with it till you got up close and personal with it.

Ric
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Old 01-27-2005, 02:05 AM
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only at idle. sounds like the map sensor vac hose is possibly collapsing. also egr ...?
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Old 01-27-2005, 02:13 AM
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tpi

Carbs Rule!!!
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Old 01-27-2005, 06:29 AM
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I had a similar (idle) problem years ago - mine would idle erratically (but no lean "pop"). I had a custom PROM burned and that fixed it. I suspect you are too lean and that is causing the pop on the throttle. You could try increasing your fuel pressure but IDK where it's at now. I ran mine at 50 psi w/305 injectors on a mild 350, but that wasn't enough compensation after I changed cams (was using a crate engine for an 87 pickup).
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Old 01-27-2005, 11:19 AM
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I am running a custom prom at the moment too. Even though I changed heads, it ran great for about 3 weeks with the new heads and no problems.

Its a mass air flow system, no MAP sensor. I'll check the vacuum lines and make sure, but even if one was closing, wouldn't that act like a closed port and not really effect idle?

Yes yes, carbs rule . But you cant beat picking up an extra 5-6MPG over the carb setup

I am going to check the O2 sensor today and see if its cracked or broke or the wire is broken. Something is keeping it from going into closed loop mode.

Oh. Its not doing any poping anymore. I can rev the engine from the idle and it revs fine. Nice and strong, no misses that I can detect.
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Old 01-27-2005, 12:15 PM
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LMAO bracketeer... yes... carb rule! all this sensor crap is just another way for the auto companies to make more money.
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Old 01-27-2005, 01:33 PM
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Yes . . . yes indeed . . . all this "sensor crap" is just a big scam

While it is a pain at times, I still believe in the technology.
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Old 01-27-2005, 02:14 PM
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Me too Siggy, i just don't always trust the people making it!

What does a simple fuel injection system need?

MAP or MAF/MAS sensor, TPS and dizzy, right?

the O2 is nice, but what's all the other junk?
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Old 01-27-2005, 03:31 PM
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It depends on the system. More modern ones use cam and crank sensors for sequential fire systems.

Older ones are batch fire meaning the injectors on the driver side all fire at once . . . then the passenger side fire. But modern systems only fire the one needing to be fired based on crank/cam position. More efficient this way. 02 is a very intrical part of the system. This is where your economy comes from. Its more than just nice to have. Its what determines how efficient the system is running, and makes chances to make the system better.

IAC (Idle air control) controls the amount of incoming air at idle. Supposed to create a smoother more efficient idle.

Intake air temp sensor helps determine cold start conditions, adding more fuel for a quicker start during cold weather. Much better than chokes.

I suppose a TPI, compared to man FI systems is probably a simple one. Although carb setups are much simpler, you'll never see the efficiency or potential that a FI system can deliver. If you could, they'd still be using carbs today.
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Old 01-27-2005, 08:04 PM
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You've probably already done this, but a sticky IAC can also cause problems like this. You might try taking it out and cleaning it and the passages in the manifold with some carb cleaner. I can sometimes get carboned up. I'm sure you've also already checked for a vac leak.

Good luck,

Dave
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Old 01-27-2005, 08:48 PM
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What is your block learn at idle?

Have you tried adjusting the TPS to a higher voltage, say .60?

Is the IAC original to the TPI, or has been replaced in the past?

Are your injectors stock, and have they ever been cleaned? I mean, professionally cleaned, not just a bottle additive. Are they gray?

Ed www.edgesz28.com
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Old 01-27-2005, 08:55 PM
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I'll have the check the block learn. I'll set the TPS up some more and try it. What does block learn refer to in the scanner? I mean I can get the reading for you, but what is the signifigance?

The IAC has been changed. It was changed about 3 months ago. The injectors are not stock. But they haven't been cleaned professionally. I'll try what I can before pulling them and having them cleaned. There is a place locally that does injector cleaning but its 120 some bucks lol. I dont mind spending it but I want to rule out other things before I do.

What part are you refereing to for the color? The main body of them is black. I believe they are 22lb/hr injectors.
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Old 01-27-2005, 09:20 PM
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Block Learn: When I converted my Suburban to TPI, I learned from Street & Performance that a block learn of 128 is considered perfect. Mine has been running about 132 which is leaner than ideal so I am trying different fuel pressures and TPS settings to bring it down. Since I blew up the trans, I haven't worked on it for a couple of weeks so I am still working on this problem. I say it is a problem only because it exhibits a slight miss at idle and S&P believes it is associated with the lean block learn number. The plugs are very white after it has been idling for a while. Worse case, they will have to adjust my chip to help correct this problem.

IAC: Was it specifically for a TPI? I learned that a TBI cone is slightly smaller and while it will work, it gets a little skippy at times. In the picture below, the left is a new TPI piece, the right a TBI piece and the bottom the orignal TPI piece.



Injectors: I had my original injectors cleaned by S&P for $120. This included new o-rings and screens. I learned AFTER that the gray "Mircotech" injectors are the worst ever installed by GM. I say worse because according to Mark Campbell at S&P, they are more problematic. Even though they were cleaned and balanced, sometimes they will leak and cause erratic idle problems. But they ran fine on the GTA. Anyway, I bought some new 24# injectors from S&P for $285 and they applied the $120 toward the new set. I have not had time to install them yet. I doubt this is a problem, but you never know. Since yours are black, it sounds like you don't have the Microtech injectors anyway.



Ed

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Old 01-27-2005, 09:41 PM
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Good to know. Thanks for the info. I beleive my injectors are different than the ones mentioned.

The IAC is for a TPI . . . that much I am sure of. Doesnt mean mine isn't bad though. The surging on the idle is so rythmic it's somewhat wierd.

The problem is that my local autoparts store is suddenly out of like EVERYTHING for this car. IAC, comupter, etc. plus they dont have a replacement for the fuel pressure tester that broke. I was hoping to have it running for this weekend but they dont get anything new until Sunday. Just isn't my week I suppose lol.

I picked up a new o2 and spark plug wires since they too were under warranty and free for me to replace. My friend had a VERY similar problem on his 85 vette, and it turned out to be the comp. It was keeping the fuel from priming as well, which mine is not . . at least yet. And something is keeping the engine from going into closed loop. I have my suspicions about the computer. If I cant get it figured out tomorrow I might give S&P a call. You seem to have good luck with them.
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