Wading in over my head

[redfury]

Need some help to make sure I don't throw money down a rabbit hole unnecessarily.

I just bought a 1998 Astro with a 5.7 Vortech from a Savanna van. The PO claimed the motor was from a 99, but the PCM in the van seems to be from a 97 truck. The Black box serv.no. is 16244210.

Here's my problem...The truck starts right up, drives through the RPM range just fine, but it idles at 1000-1500 rpm! It'll eventually drop to about 750, but if I touch the gas again, it goes back up and stays there for an undermined amount of time. Also, the tranny doesn't shift like it should, the other day it slipped like crazy ( very cold out ) and once I had driven a few miles and stopped for coffee and came out, it was shifting again. The 1-2 shift is decent, the 3rd gear seems soft and it drops into 4th heavily. I don't think it's a tranny issue...he said it was rebuilt 10k ago and there is good pressure, it's solid when it's taken out of Park and put into gear, forward and reverse.

I've been doing a lot of reading here and it seems to me that there might be a harness issue since there supposedly was a change from 97 to 98? I had a p1406 code with freeze frame data stored, as well as p0122, p0327 and p0420-30 codes set originally, but when I removed the codes with my scanner, only the EGR Pintle position code showed up again. I pulled the EGR and replaced it as the plunger seemed to stick a little ( found a nice one in the local yard that operated smoothly and in much better physical condition with a newish looking gasket under it ( assuming it was a replacement part not much before the demise of the van it was on )

I replaced the TPS as my scanner was showing 0 - 1.6 fluctuation and pulled the IAC valve to check for blockage/carbon and operation. I plugged the IAC into the harness and turned the key on to check operation, the motor moves the valve smoothly, so I don't think the IAC is causing the high idle. My next step is to do a vacuum test now that I've verified the other components.

HOWEVER, I'm stuck on the idea that this is a computer issue. The local go fast shop wants $275 to do an off dyno tune. He says as long as it has a v8 PCM, he can do it. Before I even think of shelling out that kind of money, I want to make sure I'm providing a good canvas on which to tune. I don't have the ability right now to go crazy and do a loom switch to a 411 PCM ( which I can get for 50 bucks at the local yard ), but I'm wondering about the 97 that is in there now. I wonder if it isn't cause for some of the problems there is with general driveability and if I would be better served updated the PCM to a 98-00 PCM. He claimed to have just done the extra wiring for the extra injectors, so I assume he didn't do a wiring swap with the motor, just used the existing from the 4.3. Should I expect a 98-00 PCM to be more plug and play with the motor/tranny or should I just buck up and go see the speed shop?

My driveability isn't what it should be, and I'm getting 12mpg. I know this set up is good for much better MPG.

Also, the transfer case is a pushbutton 4x4, no AWD.

I'd certainly appreciate anyone who has any advice...especially if you went through the trouble to read my little diatribe! :anitoof:

[Taz]

Hello redfury,

From your description it sounds like you have too many variables in play to make any kind of reasonable decision on how to move forward. The first thing I would suggest is confirming the accuracy of the wiring harness / PCM pinouts. This won’t cost you any money, just a few hours of your time.

Get a list of the PCM pinouts for a 1997 5.7 L Vortec truck, and confirm each wire in the harness. I use a digital voltmeter set to “continuity” with an audible tone. Unplug the 4 connectors from the PCM (blue / red / clear / black), then check each pin one at a time – with the corresponding contact at the sensor / connector.

You listed the following DTCs as being active:

P1406 - EGR pintle position
P0122 - TPS
P0327 - knock sensor bank 1
P0420 - catalyst efficiency bank 1
P0430 - catalyst efficiency bank 2

Odds are some of these will be caused by wiring issues. Confirming the wiring harness integrity as described above will assist in this diagnosis, as will confirming / cleaning all grounds.

If you’re only getting 12 MPG, then raw fuel is going out the tailpipe. This might be the cause, or at least a contributing factor, of the P0420 and P0430 DTCs being set.

Also check for vacuum leaks, coolant in the combustion chamber, and verify the distributor has been properly installed / adjusted – if it’s off a tooth or two it will never run right.

I would recommend all of the above before considering a custom tune.

If you can, confirm the tune in the PCM is a “stock” 5.7 L Vortec tune.

Lastly, a “0411” swap is very straight forward, and requires only an LS1-B PCM and connectors. The existing wiring harness is used - with generally no cutting or splicing required.


Regards,
Taz

[redfury]

Yes, I agree that a full integrity check is in order. I think I confirmed my belief that it is not a vacuum problem causing the high idle tonight though. I just got back from a test drive. I reinstalled the IAC and reset it using the key on ( 10 sec ) key off ( 5 sec ) and cleared the codes. Idles great! No codes came up during a round the block shakedown ( quicky ), but I did notice something that needs to be addressed.

The idle is right where it should be, BUT...when I put it in gear, the idle automatically raises to over 1000rpm, which in this snow, overpowers the ABS and the only way to stop efficiently is to put the van in Neutral ( idles right back down ).

So, I've got something going on in relation to the transmission and the PCM telling the engine to adjust for a higher load or ???

Never ran into this before. Thoughts?

Also, with the 4x4 conversion, I believe he added the switchbox to the underside of the dash, but it seems to be held in place with zip ties and may have a questionable ground, as while I was working, I moved it and could here relays switching. I'm going to have to ground that properly for sure.

[Taz]

There are Desired Idle Speeds (B1200 in your tune – I think) for:

in gear A/C off
in gear A/C on
in P/N A/C off
in P/N A/C on

The idle speed will increase a little when you put it in gear - at normal operating temperature.. However, when the engine is cold (ECT of -4 degrees C or less) the in gear idle may be over 1000 RPM. If the ECT sensor is faulty, or improperly wired, the PCM may “think” the engine is cold all of the time. This may also be contributory to the poor fuel economy.


Regards,
Taz

[redfury]

Do these engines have two coolant sensors? The one on the front of the motor looks like it had been replaced recently, the brass is still shiny and the thread tape is still white. I know that sometimes there are two, one of the gauge, one for the PCM.

[redfury]

Keep in mind, I have a cheap Actron Scanner that can tell me some live data, but not much more than that. I can see coolant temp, TPS, calc load, etc, but nothing more than that. When I drove off, the engine was up to temp, I know that much because it had been idling for 15 minutes before I took it out for the road test.

[Taz]

I don’t do any work on the Vortec (Gen I based) engine line. Whether you have one 2 wire coolant temp sensor, one 3 wire coolant temp sensor, or 2 sensors (one for the gauge, and one for PCM) – I have no idea.

A good quality manual will assist you greatly. Helm is the only source for GM OEM type manuals. Given the vehicle is a conversion, which you didn’t perform – a good manual will be an invaluable resource.


Regards,
Taz

[redfury]

Where does one get a manual from HELM? Never heard of them actually. All I ever end up with are the Haynes/Chilton manuals, which are essentially "cars for dummies" and I hate them with a passion. I'll take a good shop manual, I had a great one for my old 1965 Plymouth Fury III...showed you how to do everything...loved it, want one for everything I own. Reference manuals are bibles to me. Give me a fish, feed me for a day, Show me where to buy the manual, I can fix this shit myself. :mrgreen:

[Taz]

Online at www.helminc.com (http://www.helminc.com/) Select the Vehicle Owner / Do-It-Yourself / Professionals link – then search by vehicle. Guessing you will need “GMT97CK” - $135.

You could also try www.alldatadiy.com (http://www.alldatadiy.com/) – they charge $16.95 per year or $29.95 for 5 years. I have never used this service – but reviews generally seem positive.


Regards,
Taz

[redfury]

We've got Alldata at my work, it's a pretty good site and comprehensive. I might just have to drop the 30 bucks on it, might be worth it in this case.

[redfury]

I checked the coolant temp sensor cold. It read 32 degrees while the overhead temp read 18. Also, the ignition advance was -21 while idling at 1500+ RPM, running the RPM up higher netted -27.

I also looked at the calculated load, it was showing 10% at idle, but the same reading when I put the transmission in gear, brake applied. That seemed a little strange. The idle is way up there again, I'm wondering if pulling the transmission fuse and reinstalling it last night had anything to do with the sudden RPM drop and explanation for the RPM rise in gear...is there something that is triggering the IAC from the transmission that is being interpreted improperly perhaps?

[Taz]

Once you obtain a good manual, the interrelationship of components will be easier to track down. Regarding the ignition timing - if the distributor was installed incorrectly (out of phase) the timing will never be right.

The park / neutral switch on the transmission (probably has 2 plugs in your application) reports gear position to the PCM & IPC. This switch also controls the backup lights, and power to the starter relay. The PCM will alter idle speed as a result of the reported gear position.

Regarding the “load” on the engine at idle - I’m not certain if 10% with Gen I Vortecs is “normal”. With the Gen III, GM purposefully engineered in a small load at idle - to help stabilize the idle.


Regards,
Taz

[redfury]

I agree, a good manual is really needed. I just went to drive it to work and it was backfiring ( popping ) pretty badly and now it shifts out of 2nd into no gear at all, won't even drop into 4th...grrrrr! This is frustrating. Something that I did notice last night though, sitting in the driveway was that I could drop the idle down if I pushed down on the brake hard, the brake went down to the floor with some effort and the feedback was like the ABS was buzzing through the pedal. I'm wondering if I don't have a problem with the VSS, because the van has been hard to stop on the snow, the ABS seems to kick in almost immediately.

[redfury]

Well, to update this thread...the tranny shop I brought the truck to after I lost all gears but 2nd looked into the motor a little and believe that the 1/2 cylinders are getting raw fuel from the pressure regulator. Looking at the way the Vortec spider is laid out, I can believe that as being a possibility, and would explain partly the 12mpg I was getting, not to mention the back fires through the exhaust @ 3500rpm+...that and the arcing I noticed off at least one plug wire can't be helpful.

They also looked into the computer and believe that it was tuned, because there are a lot of ZERO values , but also said that the cam sensor was at 9...and I saw timing at -22 at high idle, -28 @ 3500RPM.

I'm waiting to hear back from them.

[redfury]

Final update to this thread, I swapped to a 411 PCM, tranny shifts fine. Still have to get the cam indexed, but the van runs nicely now. For anyone doing the 411 swap in a 98 Astro, you need to use Express van O2 sensors...trust me, this will save you a TON of headache. They ground out differently from what the 98 computer wants to see vs what the 411 wants to see. If you do the swap and you don't see the O2 sensors in a scan, then you have the wrong ones. Switching over the ends from the 4 flat to the 4 square plug our Astro's have is easy enough to do also....all you need is a paper clip. Push it into the opening under each of the pins and push. You are leveraging the tab in the pin UP and over the plastic retainer block inside the connector...then it's just a matter of matching ABCD and pushing the new pins into the old connector one at a time...takes 5 minutes.

[joecar]

redfury, thanks for the update.

[redfury]

No problem, I hate finding threads online that have no logical conclusion. Dead ended threads suck.

[redfury]

Well, it's time for another update to the thread now that it's been a while since I got everything sorted out. The van still runs well. I'm averaging 14.5mpg . I picked up the Torque app and a bluetooth OBD2 adapter for my smart phone. I didn't get to play with it a whole lot, but the one time I got everything to work right and had the conditions to do it, the van ( in 2wd ) did 0-60 in 7.9 sec and the quarter in 17.9 sec...think the speedo read about 90mph. This is all on a base express van tune. There is someone local that posted on CL about doing a tune for $200 for me and as soon as I can find the extra scratch, I'm going to give him a call. I'm sure with a good tune, I can get that mpg up and squeeze a little quicker times out of the van.

I need to get the IAC out of the van and get the correct o ring on it as I had pulled it out to check it for carbon, lost the red o ring and used one that I had laying around...a little too big, and now the van doesn't like to idle at all unless you reset the IAC with the key on for 10 sec and the throttle partially depressed. I may need to replace the IAC though, with the shops scan tool, I couldn't get it to operate the IAC, or if it did, there was no change in idle speed.