The Stovebolt Site Forums The Shop Area The HiPo Shop 350 engine with ECM quits at ~25mph

My dad put a 350 engine, plus the ignition and fuel system (including the ECM) from a 1989 chevy R-10 in a 1959 apache. One of the last things he told me before he died was it was running fine the last time he drove it. Truth is the last time he drove it he was still putting it together and was probably sitting on a 5-gallon bucket. The problem is it runs fine until about 25MPH and then it shuts off. If you let it coast , it will start and take off again when the speed gets back down to about 15MPH. I ran my timing light inside the cab and learned that it does stop firing about 25MPH and starts firing when it coasts down with the clutch out. Does not matter if I am in 2nd or 3rd gear so I don't think it is tied to RPM.

I used to work on these things in a previous life but I have forgotten most of it. Thanks to eBay I have a scanner old enough to read the computer so i have checked all of the sensors. The only two that are not currently connected are the O2 and Park sensors. O2 should not be a problem. I am wondering about the park sensor. It is a straight shift but the computer came off an automatic. Right now it thinks it is in park. Will the computer shut the engine off if it thinks the truck is going 25 MPH in park?

Thanks in advance for any advice. I am considering ripping it all out and putting something more modern in it. Nothing like troubleshooting a 35-year-old electrical system in a 65-year-old truck.

curtis

I would take out motor and sell........ and put in something LESS modern. Chevy V8 non computer, HEI, Carb, alternator. Plenty of them. Wiring a 55-59 truck is very easy after that. I have done many TF.

The motor is older than the electrical system. The motor had points and condenser originally and then an HEI distributor. I would prefer to not go backwards.

Every vehicle I own except the Ford pickups has points and they've never let me down in my entire life. I was once stranded when the HEI module failed in my '72 Monte Carlo a couple decades ago.

I believe the point of this forum is to help and not second guess or say you would do it differently. You will have to talk to my dad about why he did what he did. He is buried in Maplewood cemetery in Paris TN.

I asssumed it was "newer" when I read ECM. Seems like you are troubleshooting a module or an electronic modification to a motor.. You are correct, it's your Dad's legacy and your desires that matter. Sometimes helping is offering a option/second guess. It's all offered in friendship.
I do not know what "the motor is older than the electrical system" means. But that is OK, I see I'm not the right person for this post.

Getting back on topic:

Curtis: how are your technical skills? Can you trace out signals from the ECU?

You could have a couple things going on. Lets get a bit more information.

1. You said the ECU/Fuel/Ignition are from an 89. Does that include the computer controlled 89 distributor? Your other comment about points then HEI wasn't clear to me.

2. What vintage is the 350? You said it was older than the fuel system. Do you know whether it has the intake from the 89 or the intake from the engine?

3. What transmission does it have?

4. Is the ignition switch connected directly to the starter? Or does it pass through the ECU?

If you can give us that info (and maybe a picture or two of your setup?), we can dig in and give you some more helpful assistance.

Alternatively, for a modern engine, it is hard to go wrong with an LS swap. That is also something we can give you some advice on.

This might sound dumb, but what are you doing for gauges and how is the speedo connected?

Does the scanner you have let you see how fast the ECU *thinks* you are going?

If you know your tire size/rear end ratio in the TF, that would be helpful for some calculations.

The short answer is dad owned a garage and specialized in electrical and performance issues. We would send our heavy work to other shops and they would send their electrical work to us. I worked there for several years and am used to troubleshooting these systems. But it has been 32 years and I do not have access to the level of diagnostic equipment and resources we had then. It is slowly coming back as I work through this. (Like remembering the wire you disconnect to set the timing is behind the brake booster instead of near the distributor where the documentation says it is. )

Today I finally figured out it was losing fire. I had been thinking it was a fuel system problem. I put it back in the garage at that point so I could do some research.

The entire wiring harness, the electrical system (including the distributor), and TBI is from the 89 Chevy truck. So I am using the documentation for the 89 truck to work on it. The engine itself is from the 70s but that does not make any difference.

It has a digital dash and I am pretty sure the ECM is getting the speed signal from the same sensor.

The primary purpose of my post is to learn if anyone knows if the computer has a mode that would shut the engine off. Like going 25MPH in park. I don't remember in my previous life as a mechanic ever encountering that but I have never worked on a vehicle with a transplanted electrical system. I know I have replaced speed sensors but I don't remember a park sensor being bad.

Dad has had this truck since 1974. This is the second time it has been reworked. I would like to get it finished as he intended and sometime down the road I may start making modifications.


curtis

I don't believe there is a speed limit in park, but those vintage of trucks had a speed limiter of 98mph.

Depending on what rear end, tire size, transmission, and sender you have (compared to the stock one from the 89), the ECU might be triggering that.

Can you try discoonnecting the speedo sending unit at the transmission to see if that affects it?

If so, there might be some ways to work around it.

As far as the park signal, that is probably permanently jumpered because the ECU will only allow the starter to crank in park or neutral.

Per Techline, the stock trans sending unit in the 89 should have been putting out 3960 pulses per mile.

You can look at your setup in the 59 and see how your pulse per mile compares.

For a point of reference, I put a 3.73 rear end with 29.5" tires under my 58. Using the SM420 and the Dakota Digital electronic sender (screws into the speedo cable outlet), I am seeing just under 12k pulses per mile. If you have a similar setup, 25mph actual could be read at the ECU as ballpark 100mph.

A speed limiter would make a lot of sense. I will look into that. It does have a Dakota dash. He may not have had the speed sensor connected when driving it earlier. Maybe the weekend before I get it out of the garage and do any testing.

Thanks!

Good luck with figuring out your dad's truck. It sounds like he knew what he was doing. Putting together an old 350 with a more modern computer controlled fuel and ignition system in a 50's truck is not child's play.
I recently bought a '52 truck from the estate of a dear friend who passed away, and I am spending a lot of time on all kinds of detail with everything on this build which I don't normally do out of respect for my friend who isn't here anymore.
Next time I'm travelling through Paris, Tennessee, I'll make a point to swing by the Maplewood Cemetery and holler out the window to your Pops that his boy's got this, and give a resounding thumbs up.

Jr. I’ve read your post. Sounds like your Dad left you with a challenge, an opportunity. I grew up with GM TBI in the 80s and 90s and accordingly grafted a 91 GM TBI system onto a 1969 327 in my 48 3100. It runs like a dream. Guys: don’t shoot the messenger….we’re trying to help out Curtis here. There is nothing in that ECM (that I’m aware of) that would shut off your fuel or timing at 25mph, but let’s entertain a few ideas. 1) You said in your post that the computer is always seeing that you’re in “PARK”, but you have a manual trans in your truck. With your EBay scanner is that the case as you’re going down the road? How accessible is the ECM? Terminal B10 is the “PARK” input: make sure that wire is disconnected. 2) Did your Dad hook up a knock sensor up on that 70’s engine? Can you confirm if there is a knock sensor and an accommodating ESC Module (Electronic Spark Control)? 3)Does your Ebay scanner show the ECM setting any codes, like a Code 43 for ESC?

Quick work around for that Park issue. Either connect or disconnect that circuit and see if anything changes.

I'll check my '89 factory manuals, but I'm pretty sure it would just be an off/on switch or ground/not grounded signal. The mid to late 80's computers were pretty simple like that. So, if it is currently not grounded, ground it, drive it, and see if anything changes. Etc. At least, that's what I'd do. Gimme an hour or two and I'll dig up the manuals for the wiring diagram.

I concur with MNSmith….good point. The P/N input is at
B10 of the ECM Connector.

Thanks, everyone! Lots of good information. I will keep you informed.

Sorry I was short about the earlier comments. Honestly, I would have preferred keeping the truck as original as possible because it would be easier for me to work on. It is a good thing I don't have a bigger garage or I would probably drag home another one to do the way I want.

My grandfather bought a service station in 1947. I was told my first job (task) was sorting bolts at age 3. I worked full-time for my dad after college from 1988 to 1990 but I had been working summers and after school for most of my life. Digging though the wiring diagrams and reading the manuals sometimes feels like deja-vu. But it has been frustrating. The truck sat long enough while he was sick that the entire fuel system corroded. I got all of that straightened out but the doubt was always there that I was still dealing with a fuel issue.

Curtis,

Below is a URL to what I think is the best forum on the web that specializes in the early GM OBD1 TBI fuel injection stuff. Get yourself signed up and ask questions. They are a friendly bunch and super knowledgeable on exactly what you are dealing with.

Gearhead EFI

So much for relying on my memory. I looked at his notes and the electrical system is 87 instead of 89. He notes that the same ECM was used for several years.

It has a Dakota VHX dash and the manual says " for an ECM or cruise control, the SPD OUT terminal can be used. This terminal can supply a 2,000 ppm or 4,000 ppm signal."

I can see a wire connected to the SPD OUT terminal. I will have to trace it to see if it goes to the ECM. I know the dash has not been calibrated yet because I installed the buttons that control the dash. I was going to calibrate it and zero the miles on his birthday. Whoops , that was 3 weeks ago.

Its been a long time since I worked on one of those systems, but it seems like when the fuel system quits working it shuts off the ignition.
It is something to look into when you are trying to figure it out. Beings the shut off is consistent in the rpm that it is happening that probably is not the problem but I thought it might be worth considering.

George

Curtis, another thought….you said in your introductory post that you checked, with your EBay scanner, “all of the sensors” except the O2 and the PARK sensors. Have you driven it with the scanner connected and monitored the VSS up to 25 mph? That would easily confirm if your Dakota Digital Dash is connected to the ECM VSS input terminal A10, and if the dash is outputting the signal at the correct pulse (2 pulses per cable revolution). Good luck, Dave

I don't remember OBD1 being sophisticated enough to give that kind of reading. I have what was considered a decent machine back in the day and recently broke it out for some work on an 89 Mustang 302. Very rudimentary.

OBD 1 gave quite a lot of information but it wasn't readable on a computer screen.

It communicated with rudimentary Morse Code by flashing the Check Engine light on the dash a certain number of times with long and short pauses in between the flashes.

After you performed the requisite task to get the codes (flipping the key on and off a certain number of times (Dodge), jumping a wire under the hood with a paper clip and then revving the engine and turning the wheel lock to lock (Ford)) you would count the number of flashes and pauses and write them down.

Look up the numbers in a manual and see what they meant. There were dozens of different diagnostic codes.

GM had a proprietary language that they ran along side the OBD flash codes that put out a lot nore info. I am pretty sure that is what Curtis is looking at here.

There it is, my old reader.

I have an OTC2000 scanner with all of the 1980's cartridges. Most of the consumer-level scanners sold today (that I can afford) will not scan OBD-I . The O2 sensor is not installed. There is no park switch because it is a straight shift. I do not know what his plans were for that. That is the problem. I don't know what he had left to do or his plans.

I have not found if or where the ECM is connected to the speed sensor. I found the cruise control is connected to the speed-out terminal on the Dakota dash controller ( I will probably never use cruise control)

I put it on jack stands and ran it. The scanner showed no speed. The speedometer has not been calibrated yet but when it hit 20MPH the engine shut off. ( I had a timing light in the cab with me and it quit firing) As soon as it dropped below 20MPH the engine started running again. It would do it in all three gears so it is not an RPM issue. 20MPH in 2nd gear is about 2000 RPM.

I will attempt to find the end of the speed sensor wire. If I know Dad it probably has the original connector on it somewhere. He installed A/C so the wiring harness is well hidden under the dash. He did draw a few diagrams so maybe that will help.

It has overdrive. Many decades ago it had an overdrive kick-down switch that would momentarily kill the fire to disengage the overdrive. But that was if you floored it

Thanks again for all the input!

curtis

Try just unhooking the speed sensor from the transmission. That will tell you if it is being caused by the speed signal or if something else is going on.

The stock ECU would have used the speed signal for controlling the automatic. I think should work fine without a speed input.

My documentation doesn't have a pinout for your ECU, but if you determine that the speed signal to the ECU is you problem, you should be able to trace the wire from the sending unit and figure it out from there.

Is it a 1987 transmission? They still used a cable speedometer with an optical digital pulse generator in the gauges. If you have the DD sensor in the transmission going to the DD box I suspect the cruise output is being used as a VSS input for the 87 eco. You can change the pulse output from the DD so that may be something to try.

Problem Found!!!! I disconnected the overdrive governor and the problem went away. Overdrive is way down on my priorities to get working so I will leave it disconnected. After 2 years I can finally start getting it ready for the road.

Thank you everyone for the help and encouragement!

curtis

@Fannin the transmission is out of a car from the 1950s.

Is that the part that reduces power while the OD shifts?

It has been a very long time since I have used the overdrive so I had to do a little googling. Google says the governor drops the transmission out of OD when the speed drops below 30MPH and does not allow it to engage until it is over 30MPH. I remember a kick-down switch on the accelerator pedal momentarily grounds the coil and drops out the overdrive when you floor it. I'm not sure how that is supposed to work with ECM. The addition of OD predates the ECM by 20 years. If I had to take a wild guess I am going to say the wire from the coil to the kick-down switch got connected to the governor instead.

That seems plausible. It is good to hear that you are making progress.