Hi, I have a CAT C7 engine with ECM. It will turn / crank over but not fire. It'll run on easy start briefly, but seems like it's not getting fuel. Fuel pressure seems low at around 20psi. I've swapped the return line fuel pressure reg with no luck. What sort of fuel flow rate should I get from the transfer pump? I ran the transfer pump suction line from a barrel of diesel, cranked the engine over, and didn't get much flow from the output. I've also swapped the Heui pump and transfer pump off a second engine (not sure if a runner).... Still the same. Does anyone have experience with troubleshooting fuelling issues on these engines? I'm also after a wiring diagram for the ECM and engine sensors if anyone has one? I wouldn't mind checking if the ECM is getting power, and I'm not sure which pins to test. Are there any other electric tests I can do? Thanks
You posted this in the Dozer forum so I’m assuming the engine is installed in a dozer.? Can you supply a machine and engine Serial Number please.
Not in a dozer, old military vehicle I am restoring. Not sure which section to post in to be honest. Shouldn’t be anything machine specific though. Thanks
An engine serial number will still help. Does it have a hand priming pump? It can be a challenge to get the air purged from the fuel system without one.
We were tinkering with a C7 or C9 last week that was last working 5 years ago. Similar issues that you mention and it took a while to drag the fuel up into the filters as the electronic primer was apparently shot. Eventually we got it turning over but looked to me like it needed heat as the smoke was grey. Batteries were down abit and it wouldn’t quite go. We heated it up the next morning old fashioned style,put new Cat batteries on it and away it went. The new batteries seemed to help with all manner of problems that suprised me. All the warning lamps on the dash cleared up,the fuel primer now works and it starts off the button immediately now. I wonder if the new batteries energised things? It was —2 to -5 here this week
Yep has a hand prime pump. Fuel goes from tank through primary filter, into transfer pump on the front of the Heui, into the secondary canister filter with hand primer and then into the engine head and injector rail, through fuel pressure regulator and back to tank. Pic attached of engine serial number. Any help appreciated. Thanks
That’s fine but in that case we still need an engine Serial Number. There are dozens of C7 arrangements so it helps to know which one of them we are dealing with. Scratch that. We were both posting at the same time.
Put two new batteries on and it turns over at a decent rate. No smoke from the exhaust at all, which makes me wonder if the injectors are firing. I did rig up an electric diaphragm fuel pump I’ve used to replace mechanical lift pumps in the past. But it didn’t product high enough pressure. What’s the minimum pressure the transfer pump should produce or the cracking pressure of the fuel reg? Thanks
I’ll have to check and get back to you on that. A quick summary of HEUI theory. The ECM calculates a “Desired Injection Actuation Pressure”. It also measures the Actual IAP as soon as the starter is operated. If Desired IAP does not reach Actual IAP the ECM will not command the injectors to fire and you get no smoke from the chimney. I’m assuming that you don’t have access to Cat ET so the best I can suggest is to find the IAP sensor on the cylinder head and temporarily fit a pressure gauge that reads up to at least 3000 psi, 4000 would be even better. Crank the engine over and see what max reading you get. That will give an idea of the health of the HEUI pump and injectors. The sensor is mounted vertically on the LH side of the head very close to the front of the engine.
No access to CAT ET unfortunately. I don’t suppose anyone has a wiring diagram or engine workshop manual? I’ll have a look into the IAP sensor, thanks for the heads up Nige.
I’ll post one up later.
I used to maintain a couple trucks with C7's in them. Hard start and no start problems were not uncommon. One that was slow to start took a lot of cranking I put a fuel pressure gauge on it and as soon as it hit 65 PSI it would fire up. It turned out that there was a bypass valve in the fuel pump that allowed the primer pump to draw fuel past the gear pump and the plunger was leaking causing low pressure and slow pressure buildup.
Any joy with the wiring diagram / engine manual Nige? I'll have a look at the bypass valve in the transfer pump too Mekanik, thanks for that. I've been doing some reading and it seems the ECM needs at least 7.5vdc to operate when cranking. Just don't know which pins to check. Also, there is a possibility the actual injection actuation pressure sensor could be bad, if I unplug this and the HEUI pump is producing pressure then the engine should start. If not, then it could be HEUI pump. Got a few things to check now so I'll keep you posted. Thanks
Sorry. Life intervened, it happens occasionally......... Normal service should be resumed shortly. Electrical schematic on the way. Check your messages. IAP sensor is #6 in the illustration below.
Sorry, no. If the ECM is not receiving a genuine signal from the iap sensor it will log a Diagnostic Code and the engine will not start. If you unlug the sensor it will create a Code. The ECM operates on battery voltage. If your machine/truck has a 12v electrical system then the ECM must continue to operate at the reduced system voltage during the cranking period. Maybe down to 10v but I wouldn't trust it much below that.
It might be worth your while to inspect/test the fuel pressure regulator, #6 on the diagram below. #2 on the 2nd illustration is the actual regulator. Spec value for fuel pressure in the supply line to the HEUI pump is between 78-87psi at full load. Obviously cranking will be lower than that but as @mekanik posted above it's going to need a fair amount of fuel pressure before she will fire off. I dug up some other information stating 58-63psi minimum at Low Idle. As a WAG pressure while cranking probably not far off that range.
Correction. I have only just read this back to myself. It should read "If Actual IAP does not reach Desired IAP the ECM will not command the injectors to fire and you get no smoke from the chimney."
Thanks for the help Nige, managed to get it running yesterday. Turned out to be a poor +ve connection in the ECM plug. One of the pins had pushed back and wasnt mating properly, only giving 7v. Recrimped it and it fired straight up. Thanks again
Also changed the fuel reg as I wasnt convinced it was building pressure.