Motor Age Garage: Hiding in Plain Sight

Jan. 1, 2020
This van is kicking me around, Donnie told me. I had been out of the field for a few years, having traded my toolbox for a grade book, an office and classroom, laser pointer and a lab full of automotive students. My old friend and fellow drivability

Old cars still need fixing, and with the right outlook it can be downright fun.

Motor Age Garage Toyota Camry no-start vehicle won't start automotive aftermarket vehicle repair repair shop repair shops

"This van is kicking me around," Donnie told me. I had been out of the field for a few years, having traded my toolbox for a grade book, an office and classroom, laser pointer and a lab full of automotive students. My old friend and fellow drivability tech was working on a high mileage 1990 model Ford van that had eaten his lunch and his supper for several days running.

"It runs really rich when you first start it, and it puffs black smoke until it warms up. If it had datastream, I could do a lot more with it. The DTCs I get aren't telling me anything at all," he told me. This vehicle was in that peculiar Ford limbo around 1990 where it might or might not have datastream.

I fingered the OBDI connector on the Econoline and noticed that the twisted datastream wires were present at the VIP test connector.

"You do have datastream."

"What?" He was incredulous. "No way! The scan tool says no!"

"Lie to the tool," I told him. "Tell it you have an E4OD transmission."

"But it doesn't! This van has an AOD."

With a regular old AOD transmission, Ford vans didn't typically have PID data, but this one was the exception to the rule. I found out early on that if the wires are there on a Ford, the datastream is there, and that's what I was banking on. It turned out that I was right.

He did what I said, and there was the datastream. Donnie's eyes were as wide as the sun. He had been fighting this irritating problem for a week without the benefit of a window into the system. What we found was the TP sensor voltage gyrating all over the place on startup (it should hold steady near 1 volt unless you're moving the throttle), and the PCM was reacting to the in-range failure of the TP sensor with all those extra accelerator pump-imitating injector shots it has to provide as the throttle is opened. Forty minutes later, a new TP sensor was in place and the van was on its way out the door. Since this was an in-range failure, those trusty diagnostic trouble codes had turned out to be troublesome and misleading.

Another Camry Adventure

Engine controls are probably the busiest of all our automotive systems. It seems like the electronics invasion took place on the most intensely critical part of our vehicles first, and for those of us who cut our teeth on a set of points and a condenser, all that high tech hardware seemed at the time to be unnecessary for engine operation. I mean, what self-respecting person would want a solid state "black box" in control of their fuel and ignition? But as the years and miles have hurtled by, there are more and more vehicles on the road with hundreds of thousands of miles behind them, and a lot of those vehicles still run relatively trouble-free.

Electronic fuel injection has turned out to be a beautiful thing (except on those silly GM CSFI systems, of course). Be that as it may, there are a lot of links in the chain on a fuel injected machine, and some of those transient concerns can cost more labor hours in troubleshooting than the car is worth, especially if PID data isn't available via a datastream.

Jerry is a fellow employee of mine who drives older cars, and we had just replaced the mass air flow (MAF) sensor on his 1989 Maxima for an annoying no-idle problem. He was so pleased with that repair that he brought us his daughter's faded flat gray 1993 Camry. The concern had never happened when Jerry was driving, but she reported that it was likely to quit or fail to start several times a day, and that's a revolting development no matter who's at the wheel.

My OTC Genisys (upgraded to the 3.0 System earlier this year) was supposed to talk to this Camry, and yes, I had the necessary adapter on hand. But this 15-year-old rice burner just wouldn't cooperate – a scan tool is only as good as the vehicular network to which it's connected, and if the network is worthless, so is the tool.

We had choices; we could dig for the non-comm problem (how long would that take?) or we could attack this quitter the old fashioned way. Could we win the fight? It was worth a try. I had worked on Fords for years without datastream by back-probing sensors to gather voltages; it's not fun, but it is doable, especially in the case of a quitter like this one. So we fired up the Camry and waited for it to quit. Thirty minutes later, I walked by and noticed it was sitting fallow, which was a good thing. Now it was troubleshooting time. This would be simple...or so I thought.

Why Won't It Start?

Years ago when Donnie and I still worked shoulder-to-shoulder, he drew a ticket on a V6 equipped Merkur (remember those?) that would crank but wouldn't start. He fought with it for a while to the point that he became awash in perplexity.

From our earliest years of learning this stuff, we're repeatedly told that spark, fuel, compression and ignition timing are critical for any engine to start and run. Well, this Merkur had all those elements, but it simply wouldn't fire up. Then Donnie made an interesting discovery. If he removed three of the six spark plugs, it would start (albeit with lots of compression puffing out those plugless holes). The Merkur got a replacement cat converter (the old one was clogged) and it was on its way.

Well, this Camry was shaping up like that, only the exhaust wasn't plugged. It ran really well on the road until quitting time, which came fairly regularly when Jerry's daughter was driving the car.

Did we have spark? Yes, nearly an inch of ragged blue lightning popped across the spark tester gap.

Did it have fuel? Well, we hadn't checked the fuel pressure or the fuel quality yet, but our ears told us the pump was running smoothly when the engine was spinning and the injectors were certainly clicking (this one fires the injectors in pairs).

What about some weird ignition timing concern? With the timing light connected to the No. 1 wire, the spark event was happening at 5 degrees with the engine spinning, which was totally acceptable for a successful burn. I removed the air cleaner and shot a little carb spray into the intake stream to see if it would bust off on that mix, but got no results. Had fuel starvation been the case, it would have started on the carb spray, albeit briefly.

This was 50 percent annoying and 50 percent pure pleasure. Ever felt that tingle? I love it. It's always fun to sink your diagnostic chops into a problem like this. For those who haven't locked horns with one of these, there comes a point when things get personal – it's you and the machine. The students were going to learn from this and we were going to win, one way or another.

Looking Harder

I connected a digital fuel pressure gauge to the fuel filter with a banjo bolt adapter. If a fuel pressure drop was causing the stalling, the gauge would tell the tale. I've done this dozens of times on quitters, and you don't need an electronic gauge to do it. Let it run until it quits (sometimes for several hours), and if the pump is bad, you'll walk by and see the pressure down to around 5 or 10 pounds and the engine will be dead. If you start it at that point and the pressure bounces back to the norm, then fades away to low pressure again (usually it will if the pump is dying) well, you've fingered a weak pump that needs to be retired.

On the Camry, the pressure was at 41 pounds when the engine died. It was time to see if we had water in the fuel.

Disconnecting the fuel line back at the tank, we connected a hose, energized the pump and let the Camry empty its several gallons of fuel into a clean, safe container. When the tank was empty, we didn't see any water at all, and further testing revealed only about 2 percent alcohol in the mix. We pumped the nice clean fuel back in. No cigar there.

Now it was time to bust out the O-scope. The most sensible trace I could think of to begin with was the injector pulse, and what I found was pretty interesting. During no-starts after quit events, the pulse was very wide, as much as 130 milliseconds on the initial spin. With good fuel pressure, that's a deal-breaker, but why wasn't it fouling the plugs? It always re-started when it cooled off. I noticed that during a normal start the pulse was only 20 percent of that. I also noticed that as the engine was running with the injector trace on the screen, the pulse would periodically widen erratically and suddenly for no apparent reason. I was closing in on the cause of my no-start, and like the camel, I now had my proverbial nose under the tent.

Pay Dirt

Investigating further, I targeted a time when the Camry was starting just fine, then disconnected the fuel pump and created my very own no-start. Was the PCM expanding the pulse width trying to get the engine to start, or was the wide pulse the reason for the concern? The pulse never went over about 10 milliseconds, even with no fuel pressure, so the wide pulse was affected by some other cause, but what was that cause?

The crank and cam sensors provide injector timing on speed density systems, but the ECT, TP, MAP and IAT are modifying inputs. So I started with the easiest sensor to access and found my problem. The ECT was spending an awful lot of its time at or near 5 volts, which was reporting a very cold engine, thus the wide pulse.

Disconnecting the sensor when the no-start was present obviously defaulted the ECT reading to match IAC, which allowed the engine to start normally. Plugging the sensor back in would kill the engine or cause it to run rough.

Conclusions

It goes without saying that a Toyota guru would have sent me straight to the ECT sensor, for this concern, but the road we took, while it may have been less traveled, was a lot more fun. And, as I had decided early on, we won the battle. The Camry is back in the wind.

About the Author

Richard McCuistian

Richard McCuistian is an ASE certified Master Auto Technician and was a professional mechanic for more than 25 years, followed by 18 years as an automotive instructor at LBW Community College in Opp, AL. Richard is now retired from teaching and still works as a freelance writer for Motor Age and various Automotive Training groups.

Sponsored Recommendations

Best Body Shop and the 360-Degree-Concept

Spanesi ‘360-Degree-Concept’ Enables Kansas Body Shop to Complete High-Quality Repairs

ADAS Applications: What They Are & What They Do

Learn how ADAS utilizes sensors such as radar, sonar, lidar and cameras to perceive the world around the vehicle, and either provide critical information to the driver or take...

Banking on Bigger Profits with a Heavy-Duty Truck Paint Booth

The addition of a heavy-duty paint booth for oversized trucks & vehicles can open the door to new or expanded service opportunities.

Boosting Your Shop's Bottom Line with an Extended Height Paint Booths

Discover how the investment in an extended-height paint booth is a game-changer for most collision shops with this Free Guide.