1st TBI Conversion Help Needed

[Dougnsalem]

The balancer timing mark is at 0 on the tab at 12 o'clock. I don't understand your second question (TDC for #6.)

I don't recall another tab location. The power steering pump is in the way, but I will look.

That tells me it isn't the original engine cover and balancer combo.

But it shouldn't matter as long as the two are paired correctly, right?

I have never removed the balancer or timing cover, and the truck ran great carbed before I began this debacle.

Ok. You should be fine with the balancer/ timing tab locations.

It easy to toss the wrong balancer on it, which will make it nearly impossible to time with a light. Which I have done when I was in a rush.

 

[4WDKC]

Ok. I missed that earlier. Seems like you're on the right track with the map/iac stuff. At least it makes sense....


And just to clarify for the future. 4WDKC was right about the different timing locations, but the newer one is at 12 o'clock

You must be registered for see images attach

Again, not an issue here....

The one on my 87 is in the 80-86 position not in the post 86 it has what appears to be a factory cover also. Ill have to chekc that chrome pos on my vette see where it is.

 

[Dougnsalem]

The one on my 87 is in the 80-86 position not in the post 86 it has what appears to be a factory cover also. Ill have to chekc that chrome pos on my vette see where it is.

Yeah, when I see stuff like that, I start looking at motor id suffix #'s, casting numbers, date codes.... Someone has changed it, unless they just used a leftover at the factory.... (Highly doubtful)

 

[Dougnsalem]

Just curious @Matt Braun , how long have you had the truck? Did you get any history on it?

 

[4WDKC]

Yeah, when I see stuff like that, I start looking at motor id suffix #'s, casting numbers, date codes.... Someone has changed it, unless they just used a leftover at the factory.... (Highly doubtful)

It makes sense to me, TBI was first introduced in 86 for the Commiefornia models so that would have gotten the 86 balancer and timing cover. casting number 10054727 for the block, it had 193 heads on it and a piss poor cam that measured in under .400 lift with 1.5 rockers. According to what i have found that is a period correct block and cam for the early tbi engines, the later tbis have a better cam in them and the tbi replacement is based on the later tbi builds. Also explains why that 350 only seemed to get louder above 3k rpm and not more powerful.

 

[MtBraun]

Just curious @Matt Braun , how long have you had the truck? Did you get any history on it?

My son bought in the fall of 2016 from a friend's father. It was sitting in a barn with a snowplow on it, presumably used for plowing this person's property. That's all the history we have. Judging on the condition of the floor, rockers, and corners its been a MN or northern plains truck its whole life. Some fool scabbed in replacement floor panels at one time...not cut and weld in, but "caulk" and lay flat over the old rust.

Last winter we had an external head gasket leak so we pulled the heads and replaced head gaskets. The cylinder bores looked beautiful...so I'm pretty sure it's been rebuilt at some point.

 

[Dougnsalem]

It makes sense to me, TBI was first introduced in 86 for the Commiefornia models so that would have gotten the 86 balancer and timing cover. casting number 10054727 for the block, it had 193 heads on it and a piss poor cam that measured in under .400 lift with 1.5 rockers. According to what i have found that is a period correct block and cam for the early tbi engines, the later tbis have a better cam in them and the tbi replacement is based on the later tbi builds. Also explains why that 350 only seemed to get louder above 3k rpm and not more powerful.

That's good info to know. Any idea why your 87 would still have the older timing marks? Using up the old stuff in this case? Leftover 86 motor?

 

[Dougnsalem]

My son bought in the fall of 2016 from a friend's father. It was sitting in a barn with a snowplow on it, presumably used for plowing this person's property. That's all the history we have. Judging on the condition of the floor, rockers, and corners its been a MN or northern plains truck its whole life. Some fool scabbed in replacement floor panels at one time...not cut and weld in, but "caulk" and lay flat over the old rust.

Last winter we had an external head gasket leak so we pulled the heads and replaced head gaskets. The cylinder bores looked beautiful...so I'm pretty sure it's been rebuilt at some point.

Man, what people do..... Caulking a floorpan in is up there.... Lol. So yeah, someone probably just replaced both of those, if the timing marks are right on the money. I did once because my early cover was chrome, and it leaked everywhere...

And after you mentioned it, I do remember you talking about the head gasket and cylinders. Too many people here for my memory to keep stuff straight... Lol

 

[4WDKC]

That's good info to know. Any idea why your 87 would still have the older timing marks? Using up the old stuff in this case? Leftover 86 motor?

Could be, or it could have been planned that way at the engine shop because they didnt have the new parts manufactured,shipped, delivered or planned to put in the squarebody. No way of knowing what happened.

 

[1987 GMC Jimmy]

After you pointed out the vacuum issue I paid closer attention to it when driving, and I think I just caught a frame precisely when it backfired/cutout, which dramatically lowered the vacuum. When driving it since it holds a pretty steady 18-19 vacuum. It will dip when accelerating, but then recovers to the correct level.

I found this though on IAC counts at zero, meaning it is completely closed.

There is a vacuum leak allowing unmetered air to enter the engine

· The throttle stop screw is adjusted incorrectly (throttle being held open too far; more on this later)

· There is a problem with the throttle cable or cruise control system that isn’t allowing the throttle to close all of the way

· The IAC valve itself is faulty

Soooo, the only vacuum related item I haven't replaced is the MAP and the check valve at the brake booster. I never sprayed the brake booster with ether either. Never thought of it till now. I'm confident the TB base gasket and other vacuum lines into the TB are sealed.

To test the MAP, simply unplug it and plug the TB port? If it runs better then that is the problem?

The IAC thing doesn’t sound right to me at all. I never opened up my throttle stop screw because I was worried about what would happen if I was tempted to mess with it. If it has been adjusted, the setting could possibly incorrect with something binding in there, but I’d deal with the IACV first. If the cruise servo is suspect, simply disconnect the servo lever. That’s happened to me where something wasn’t right with it, and the throttle got stuck. What’s your cruise setup? Do you have an 84 or later cluster with the VSS buffer for the ECM, or are you still running the original cruise setup? Is the throttle cable really stiff or not bad? I had to replace mine because it was too stiff, but I don’t think it ever bound up. I don’t know if the IACV is getting faulty info or if it’s the valve itself. The voltage diagram doesn’t offer any meaningful test either so I’d try another valve to see what happens. If you want to test the booster and check valve, you can remove and plug the line and do manual brakes to see if the issues improve. A bad booster and/or check valve will have either a loud huff when you press the brakes or the brakes will feel hard. As far as the MAP goes, I’d do that and unplug the connector just to be safe. It should throw a code and defer to a richer mixture, but that’s it. The textbook test is to pump it up with a Mityvac and test the voltages at x vacuum levels, which I’ll attach.

http://troubleshootmyvehicle.com/gm/2.2L/how-to-test-the-map-sensor-1

 

[MtBraun]

The IAC thing doesn’t sound right to me at all. I never opened up my throttle stop screw because I was worried about what would happen if I was tempted to mess with it. If it has been adjusted, the setting could possibly incorrect with something binding in there, but I’d deal with the IACV first. If the cruise servo is suspect, simply disconnect the servo lever. That’s happened to me where something wasn’t right with it, and the throttle got stuck. What’s your cruise setup? Do you have an 84 or later cluster with the VSS buffer for the ECM, or are you still running the original cruise setup? Is the throttle cable really stiff or not bad? I had to replace mine because it was too stiff, but I don’t think it ever bound up. I don’t know if the IACV is getting faulty info or if it’s the valve itself. The voltage diagram doesn’t offer any meaningful test either so I’d try another valve to see what happens. If you want to test the booster and check valve, you can remove and plug the line and do manual brakes to see if the issues improve. A bad booster and/or check valve will have either a loud huff when you press the brakes or the brakes will feel hard. As far as the MAP goes, I’d do that and unplug the connector just to be safe. It should throw a code and defer to a richer mixture, but that’s it. The textbook test is to pump it up with a Mityvac and test the voltages at x vacuum levels, which I’ll attach.

http://troubleshootmyvehicle.com/gm/2.2L/how-to-test-the-map-sensor-1

I agree the IAC doesn't make sense. Need to dig into this further. I have no cruise. Original 78 cluster. There is a JTR speed sensor connected to ECM - should not impact this problem. I double checked my brake booster and I lose no pressure when holding the brake and turning off the key after running. So the check valve and vacuum booster should be ok. But to be sure I'll completely unhook and plug the vacuum port. That only leaves the MAP sensor or the throttle blade itself. Need to look at both the throttle and detent cables and check for interference.

I had also read not to jack with the throttle idle position screw but when Kacy forwarded the gearhead post by Eagle Mark I figured it was ok. But, if I have a air leak else where (MAP) then I won't be able to properly adjust the throttle anyway, which might explain my zero IAC count and the fact that idle wouldn't settle to 700 RPMs.

I don't think its the IAC valve itself. The symptoms were unchanged when I put in a new one.

 

[MtBraun]

I tested the MAP sensor according to the link above and my tested voltages were approximately .25 volts below each of the following vacuum levels:

1.) 0 in. Hg ...... 4.7 Volts.

2.) 5 in. Hg ...... 3.9 Volts.

3.) 10 in. Hg .... 3.0 Volts.

4.) 20 in. Hg .... 1.1 Volts.

I don't think this is enough to suggest a faulty MAP. Its moving with changes in vacuum so isn't that the main thing?

I then disconnected the MAP circuit and vacuum line, and plugged the vacuum port on TBI. At the same time I unhooked the brake booster vacuum line and plugged the port.

Took for a drive, it ran a little choppy but once warmed up I noticed my IAC counts settled in to normal range. I hooked the MAP and brake booster back up, drove it and my IAC went down to zero. So I have a vacuum leak in either the MAP or the brake booster. I got a new booster check valve but haven't been able to hook up and drive.

 

[MtBraun]

Oh, and the throttle and detent cables operate smoothly, no catches or hang ups. The throttle blades close nicely.

 

[4WDKC]

I tested the MAP sensor according to the link above and my tested voltages were approximately .25 volts below each of the following vacuum levels:

1.) 0 in. Hg ...... 4.7 Volts.

2.) 5 in. Hg ...... 3.9 Volts.

3.) 10 in. Hg .... 3.0 Volts.

4.) 20 in. Hg .... 1.1 Volts.

I don't think this is enough to suggest a faulty MAP. Its moving with changes in vacuum so isn't that the main thing?

I then disconnected the MAP circuit and vacuum line, and plugged the vacuum port on TBI. At the same time I unhooked the brake booster vacuum line and plugged the port.

Took for a drive, it ran a little choppy but once warmed up I noticed my IAC counts settled in to normal range. I hooked the MAP and brake booster back up, drove it and my IAC went down to zero. So I have a vacuum leak in either the MAP or the brake booster. I got a new booster check valve but haven't been able to hook up and drive.

What is the normal range you are referring to? As I am learning to tune my engine my IAC count was up to 145, this being due to new heads and cam but first steps of tuning is to get it to idle warm in the rpm range indicated with the IAC count between 10-20.

 

[MtBraun]

What is the normal range you are referring to? As I am learning to tune my engine my IAC count was up to 145, this being due to new heads and cam but first steps of tuning is to get it to idle warm in the rpm range indicated with the IAC count between 10-20.

The IAC settled to 25 when warmed up, with MAP and brake booster unhooked and plugged.