Having more problems with my engine. Maybe you all have some ideas.

First off, I am running a 350 (on a 66 GMC) with a MAF TPI system on it. Its an 86 system. It is not throwing any codes, and the sensor readings seem normal. Fuel pressure is at 47 and seems okay as well. Base Timing is at 8, but has been tried higher and lower.

Right now it seems to idle great. Nice throttle response and pretty smooth. However, when I put it into reverse or drive, the idle drops suddenly and it dies. If I feather the gas a bit, I can keep it alive and once it makes the transition into gear, it will stay. It will idle okay for a bit, but then it becomes choppy like its missing. It also have it idle pretty high in park . . . around 1000RPM, because anything lower than that, and it dies for sure when I put it in drive. I hooked up my timing light with the EST plugged in to see how far the engine is advancing the idle at 1000 rpm. At 1000 RPM it was at 36. Is this normal?

There are no vacuum leaks I can detect. I plugged the line for the Transmission modulator, thinking that it might be going out or something. If I pull the PCV line and take out the valve and let the line sit there, the idle picks up and it idles higher but still smooth.

If I set the idle up, and drive it, it drives decent (not like it should tho) and seems to flutter if I give it a lot of throttle.

Just seems wierd that it idles great in park, but the idle will vary when its in gear.

The last thing I put on was heads, however I had it running great with them. I replaced the manifold gasket recently as it was leaking a bit and put all new gaskets on the upper manifold. Like I said, no leaks that I can detect.

Any ideas? Anything I am leaving out that you need to know?

 

I'm not sure about that timing value but don't think it is bad. It sounds more like an idle speed control issue which is usually related to the IAC.

Clean the IAC pintel & bore and the TB bore & plates.

Then set up base idle to 450rpm and TPS min/max voltages.

 

I'd also check the MAF sensor. Is the engine going closed loop?

Try tapping the MAF with the handle of a screwdriver and if the engine stumbles the MAF is bad.

You can try unplugging it and if the engine runs better the MAF is bad.

A vaccum gauge can be used to check for a vaccum leak. the needle should hold steady. I can only speculate on the actual reading because so much depends on the cam and the timing.

36 degrees at 1000 seems high to me. I'm thinking it should be in the high 20s, but that wouldn't account for your part throttle problems.

Easiest way would be to use a real-time data logger like Diacom or a ScanTool to seen what all the sensors are reading. Sounds like one of them is out of range.

Jake

 

I have a hand held scan tool that gives me sensor readings. MAF grams per second seem fine, but I'll try tapping on it.

I'll set the IAC and TPS at 450 RPM. I dont know if it will run that low lol.

 

Actually, no.

The IAC is controlled by the ECM/PROM which sends voltage to it that is shown as counts on a screen like Diacoms. The counts should be in the low 20s.

There is a procedure for resetting the IAC, but it normally isn't needed since the IAC automatically resets itself each time the engine is shut down and restarted.

The procedure involves jumping the ALDL, turning the key to ON for about 30 seconds (don't start the engine) and while the key is still ON, unpluging the IAC. Then remove the jumper wire, start the engine, set the idle RPM using the torx screw on the throttle body. Shut down the engine, reset the TPS, plug in the IAC and start the engine.

The TPS setting calls for a voltage setting, not RPMs. .54 (+/- .075) is the correct voltage. The reading is taken with a digital voltmeter with the engine OFF and the ignition key ON. Use the top and middle TPS wires to get the voltage reading; the bottom wire is just a 5 volt reference signal.

Keep us posted.

Jake

 

siggy, try turning on the A/C when the car's warmed up, which will allow the A/C compressor to kick in. at this point the idle speed should stay rock solid or maybe a bit higher. if it bogs or stalls, it's probably the IAC valve or the signal going to it.

if the A/C test goes OK it may be that the ECM is not seeing the signal from the PRNDL, if such a signal is used in your setup. a PRNDL signal can be used in idle control to bump open the IAC valve when you transition from P/N to R/D. if that signal is faulty, the regular IAC closed-loop speed control needs to compensate, which usually happens on the order of a second or two. the closed loop control by itself is usually not fast enough to compensate for the load changes in shift transitions and the car stalls.

go with Jake's suggestion too and check the IAC counts to see if it doesn't move, or if it's stuck open or closed.

 

The vehicle doesn't have A/C on it.

I am familair with the procedures for setting the TPS and IAC, I'll do so tomorrow in the AM.

Its a TPI thats been retrofit onto a 74 350. Its running a Th-350 that isn't integrated in anyway to the computer. Its been running great for about a year. Only now has it been acting up.

Before I did the intake manifold, it was having similair problems with one difference. It would idle great and drive okay, but after giving it anything over half throttle, the engine would cut out, like spark was suddenly lost, then it would catch itself and keep going. The engine light would come on for a second, like it does when the ignition is on but engine off.

Perhaps the coil or module are losing power?

 

That timing sounds wacko to me.Set it correctly.Did you put your dist. in a tooth off?

 

I am pretty sure it was set in correctly. It will idle pretty great and even rev nicely in park. But in order to have any hope of putting it into gear and not killing it I have to run it at a very high idle. If i start it in gear and drive it, it drives okay, but I can feel the engine fluttering a bit, feeling really underpowered. I am going to dink around with it today and reset everything, and clean the IAC and throttle body. I'll also test the ignition module and coil to make sure they aren't on the weak side.

 

He has the timing set properly. He said it was a 8*. The distributor is not off a tooth. The 36* at 1000 rpms, with the ESC connected does sound high, though. I would expect to see it somewhere in the low 20's.If you haven't disconnected the battery since the light came on, you should still have the code stored. Pull that code. It could help a lot. My money is on plugged up IAC passages. I'm sure you are using the "minimum air" adjustment screw to set that 1000 rpm idle. With the IAC blocked off (see Jake's procedure) the minimum air screw should be set to 450-500 rpm. A properly operating IAC should maintain a good idle. Set the TPS voltage after the minimum air adjustment.

RACE ON!!!

 

There are a number of different things that can cause your problem. The only way to find the source is to check them out one at a time.

A data logger, as I mentioned before, like Diacom can tell you if one of the sensors is out of range. It would help if you post the readings you're getting from the test equipment you're using.

Here are some of the things that would help us:

Idle quality in both neutral/park and in gear (is it steady or jumping), BLM and Intergator values,
Ignition timing,
RPM (both desired and actual),
Loop status (open or closed),
TPS voltage,
Coolant Temp,
02 voltage and transitions,
Commanded A/F ratio,
Injector pulse width,
Any Knock Retard and Counts,
Learn Control status (On or Off) and
Mixture status (should cycle between rich and lean).

You should also attach a vacuum gauge to the engine and check the reading difference between what you get with the trans in neutral/park and in gear (if you have an auto trans).

It could be something as simple as a vacuum leak or a broken MAF wire.

I agree, too, try pulling any stored code by jumpering the ALDL A&B terminals. After doing that, disconnect the battery for about 30 seconds, reconnect it, re-fire the engine and see if the problem still exists.

Many of the larger auto parts stores, like AutoZone, can check the ignition module for free.

Have you by any chance been under the valve covers adjusting lifter preload? A lifter set too tightly can cause problems. Generally you'd notice that kind of problem at idle too though, not just at part throttle acceleration.

Many of us have walked this road before; hang in there it's solvable

Hope this helps.

Jake

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