How to troubleshoot erratic tachometer? (TBI)

[DerekTheGreat]

Haha, that is the most important part of the thread, certainly where my interest is these days. I've semi thought about selling everything I have with tires save for what I actually need.

Speakers are a pair of nice UREI 813C's and some custom cabinets housing two JBL 2245H subwoofers. On a quest to achieve 120 ish dBC and while I enjoy my XPL200's immensely, I don't think they'll get me there.

 

[PlayingWithTBI]

What's the fuel injection switch on pin B?

That's the power supply to the ESC module. Here's the schematic for an 88.

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[DerekTheGreat]

Hmm, so unless I'm a complete idiot and am missing something, all the ESC module does is communicate knock events to the ECM? If that's the case, then it's something I can rule out of the equation, no?

 

[PlayingWithTBI]

all the ESC module does is communicate knock events to the ECM?

Yepper!

 

[DerekTheGreat]

Welp, complete distributor made of 98.9% pure Chinesium has been obtained. New coil too, a Standard Motor Products. Would have went with A/C Smelco but they wanted $400 for their dizzy and it comes sans cap & rotor. Their coil only had a one year guarantee. Both the Standard and Chinesium dizzy have a lifetime guarantee, and that's the important part for me at this point, given how frequently my truck has been eating ignition components. The underlying issue remains to be seen, need help from another set of hands to do the jiggle-wiggle boogie. That's next before the Rock Auto parts go back to where they came from.

Guarantee?

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Chicken wings sound pretty good right about now..

 

[packer0440]

Just wanted to comment as I was just having a similar issue. Truck ran fine, had plenty of power, didn't randomly cut out. However I did notice that in the lower gears, or sometimes at idle, tach would flutter. Also occurred sometimes when cruising or very slight throttle application in higher gears, would quit fluttering when I gave it any more umph than that. Thought it was just a bad tach, as cluster had 350k miles.

Saw this thread, and really payed attention to the flutter, and you could feel a little miss when it was fluttering. So I changed the ignition coil first, as it was pretty old, but did nothing. Then, grabbed a spare distributor I had, happened to have an OEM GM ICM on it. Swapped with the ICM that was on the truck (GM, but looked different, probably replacement) with a little extra thermal paste, problem completely gone. Not a huge change, but runs smoother overall and no tach flutter whatsoever now.

BTW truck is a 1990 with a 454 tbi, NV4500 trans (swapped from SM465), also swapped moonies for later tach cluster.

 

[DerekTheGreat]

Thank you for the reply, packer. Glad it could be of use to another member. Seems like your experience pointed directly to a bad pick-up coil. Been working on the fiancée's Tahoe so mine didn't get any love over the weekend, but will this afternoon. Don't have the extra hands to do the jiggle-wiggle, so I'm going to swap parts first and answer those questions later. Also, running out of time to get the suspect parts back to Rock Auto. The arm chair quarterback within me suspects wonky electronics as now that's been pretty cold in the morning, I haven't noticed any flutter. But when the engine gets hot and continues to stay hot- flutter. It flutters most around idle and low RPM cruise- never flutters under moderate or better acceleration and even tapping the gas while it's acting up causes it to go away. Leads me to suspect some sort of slop in the distributor and perhaps that's what the problem with the pick-up coil is. Current distributor is some ultra cheap thing from the China express, maybe just over two years old.

 

[packer0440]

Thank you for the reply, packer. Glad it could be of use to another member. Seems like your experience pointed directly to a bad pick-up coil. Been working on the fiancée's Tahoe so mine didn't get any love over the weekend, but will this afternoon. Don't have the extra hands to do the jiggle-wiggle, so I'm going to swap parts first and answer those questions later. Also, running out of time to get the suspect parts back to Rock Auto. The arm chair quarterback within me suspects wonky electronics as now that's been pretty cold in the morning, I haven't noticed any flutter. But when the engine gets hot and continues to stay hot- flutter. It flutters most around idle and low RPM cruise- never flutters under moderate or better acceleration and even tapping the gas while it's acting up causes it to go away. Leads me to suspect some sort of slop in the distributor and perhaps that's what the problem with the pick-up coil is. Current distributor is some ultra cheap thing from the China express, maybe just over two years old.

I thought I was headed toward a pickup coil problem, but I remembered I had the extra module, figured it was worth a shot, easier than pulling the distributor, turned out to be the issue.

Like somebody mentioned earlier in the thread, it’s a good idea to grab extra things like distributors and such from the salvage yard. The OEM ones are pretty well made, still plenty of them just sitting there. All you need is a distributor wrench and they’ll sell them cheap with the module and cap on them

 

[DerekTheGreat]

Oh. Well, last week I put a new A/C Delco ICM and Delphi coil on it, still flutters. Was worse with Delphi coil, so put the old one back in and it was much better. Flutters less and less as time goes on, but not road trip confidence inspiring so it is going under the knife once more. So I suspect khrappy new parts, bad pick-up coil or wiring issue as others have mentioned. I'll get to the bottom of it one way or the other.

What are the other details of your truck? Clearance lights? Regular or extended cab? Truck in your sig says '92, so assuming you have two trucks?

 

[packer0440]

Oh. Well, last week I put a new A/C Delco ICM and Delphi coil on it, still flutters. Was worse with Delphi coil, so put the old one back in and it was much better. Flutters less and less as time goes on, but not road trip confidence inspiring so it is going under the knife once more. So I suspect khrappy new parts, bad pick-up coil or wiring issue as others have mentioned. I'll get to the bottom of it one way or the other.

What are the other details of your truck? Clearance lights? Regular or extended cab? Truck in your sig says '92, so assuming you have two trucks?

Yea I just fixed up a 1990, I’ll probably put up a thread on it soon. Luckily on the 92 everything works flawless and is basically original (even the bulbs except for a couple taillights), so it’s easy to just compare the two to since they have basically the same motor (454) to see if it’s running correctly.

The 1990 is a k3500 reg cab. Motor is stock and has around 295k on it but is still pretty strong. Has clearance lights, which I like the look of. It’s a Scottsdale, so has AC, tilt/cruise, but no power windows. Like I mentioned earlier, swapped from the SM465 to NV4500. Been a pretty good truck so far